Contractor Calculators

Concrete Calculator

Cubic yards for a slab, footing or column, plus the bags if you are mixing on site.

Cubic yards = length (ft) × width (ft) × thickness (ft) ÷ 27

How do I calculate concrete for a slab?

Multiply length x width x depth (all in feet) to get cubic feet, then divide by 27 to convert to cubic yards. For example, a 20 ft x 10 ft slab at 4 inches deep: 20 x 10 x 0.333 = 66.67 cu ft / 27 = 2.47 cubic yards. Always add 5-15% for waste.

How many bags of concrete are in a cubic yard?

A cubic yard equals 27 cubic feet. A 60lb bag of premix concrete yields approximately 0.45 cubic feet, so you need about 60 bags per cubic yard. An 80lb bag yields about 0.6 cubic feet, requiring about 45 bags per cubic yard.

How much does a yard of concrete cost?

Ready-mix concrete typically costs $125-$175 per cubic yard, depending on your location, the mix design, and delivery distance. Specialty mixes (high-strength, fiber-reinforced) can cost $150-$250 per yard. Most suppliers require a minimum order of 1 yard.

What is a good waste factor for concrete?

A waste factor of 5-10% is standard for simple slabs and footings. Use 10-15% for irregular shapes, stairs, or projects where formwork is imprecise. Over-ordering is far better than under-ordering, as short loads and callbacks are very expensive.

How do I calculate concrete for a round column?

Use the cylinder formula: Volume = pi x radius^2 x height. Measure the diameter in feet, divide by 2 for the radius, then multiply pi x r^2 x height. Divide the result by 27 to get cubic yards.

Roofing Calculator

Squares of shingles from a footprint and a pitch, with ridge, starter and waste.

Roof area = footprint area × slope factor; squares = roof area ÷ 100

What is a roofing square?

A roofing square is a unit of measurement equal to 100 square feet of roof area. It is the standard unit used by contractors to price and order roofing materials. For example, a 2,000 sq ft roof equals 20 roofing squares.

How does roof pitch affect the area?

Roof pitch increases the actual surface area compared to the flat footprint. A pitch multiplier converts the footprint to actual roof area. For example, a 6/12 pitch has a multiplier of 1.118, meaning the roof area is 11.8% larger than the footprint. A 12/12 (45-degree) pitch has a multiplier of 1.414 — 41.4% more area.

How many bundles of shingles per square?

Standard three-tab and architectural shingles require 3 bundles per roofing square (100 sq ft). Some premium or specialty shingles may require 4-5 bundles per square. Always check the manufacturer specifications on the bundle wrapper.

What are the most common roof pitches?

The most common residential roof pitches are 4/12 through 8/12. A 4/12 pitch is the minimum for standard asphalt shingles. 6/12 is the most common for new construction. Pitches above 8/12 are steeper and may require additional safety equipment and labor, increasing cost.

How much waste factor should I add for roofing?

A standard waste factor for roofing is 10-15%. Use 10% for simple gable roofs with few penetrations. Use 15% for complex roofs with multiple valleys, hips, dormers, or skylights. The waste accounts for cuts, starter strips, and material that cannot be reused.

Drywall Calculator

Sheets, screws, joint compound and tape for a room, walls and ceiling.

Sheets = (wall area + ceiling area) ÷ 32 sq ft per 4×8 sheet × (1 + waste)

How many sheets of drywall do I need for a room?

Calculate the total wall area (perimeter x height), add ceiling area if needed, then subtract openings (doors ~21 sq ft, windows ~15 sq ft). Divide total area by the sheet size (32 sq ft for 4x8, 40 sq ft for 4x10, 48 sq ft for 4x12) and add 10% for waste. A standard 12x12 room with 8ft ceilings needs about 12-14 sheets of 4x8 drywall.

What drywall thickness should I use?

1/2-inch drywall is the standard for walls in residential construction. Use 5/8-inch for ceilings (to prevent sagging), fire-rated walls, and sound-dampening applications. 1/4-inch drywall is used for curved walls and overlay work. 3/8-inch is occasionally used for repairs or double-layer applications.

How much joint compound do I need per sheet of drywall?

Plan for approximately 0.065 gallons (about 1/4 quart) of ready-mix joint compound per square foot of drywall. A 4x8 sheet needs about 2 gallons for three coats (taping, blocking, and finishing). A 5-gallon bucket covers approximately 80 square feet for all three coats.

How many drywall screws per sheet?

Use approximately 32 screws per 4x8 sheet when framing is 16 inches on center. Screws should be spaced 12 inches apart on the edges and 16 inches apart in the field. Ceiling sheets require screws every 12 inches on center. Plan for about 1 pound of screws per 8 sheets.

Is drywall estimation tested on the FL contractor exam?

Yes, material estimation including drywall is tested under the Project Management Part E (Construction Methods) of the Florida General Contractor exam. You may need to calculate wall area, number of sheets, and material quantities for a given room scenario.

Lumber Calculator

Board feet for an order and stud counts for a wall at 16 or 24 inches on centre.

Board feet = thickness (in) × width (in) × length (ft) ÷ 12; studs = wall length ÷ spacing + 1

What is a board foot?

A board foot is a unit of volume for lumber equal to 144 cubic inches (12" x 12" x 1"). The formula is: Board Feet = (Thickness in inches x Width in inches x Length in feet) / 12. For example, a 2x6x10 board contains (2 x 6 x 10) / 12 = 10 board feet. Note that "nominal" dimensions (2x4, 2x6) are used for board foot calculations, not actual dimensions.

How do I calculate the number of studs for a wall?

Divide the wall length (in inches) by the stud spacing (16" or 24" on center), then add 1 for the end stud. For a 12-foot wall at 16" OC: (144 inches / 16) + 1 = 10 studs. Add extra studs for corners, door/window framing, and intersecting walls. You also need top and bottom plates: 2 plates x wall length.

What is the difference between 16 and 24 on center stud spacing?

16 inches on center (OC) is the standard spacing for load-bearing walls and is required by most building codes for exterior walls. 24 inches OC is acceptable for interior non-load-bearing walls and some engineered wall systems. 16" OC uses more lumber but provides a stronger wall that better supports drywall and siding.

How do I estimate lumber costs?

Lumber is priced either per board foot or per linear foot depending on the supplier. Dimensional lumber (2x4, 2x6, etc.) is typically priced per piece or per linear foot. Hardwoods and specialty wood are priced per board foot. Multiply the total board feet or linear feet by the price per unit, then add 10-15% for waste.

Is lumber estimation tested on the FL contractor exam?

Yes. The Project Management Part E of the Florida General Contractor exam includes material estimation questions. You may be asked to calculate board feet, number of studs, or total lumber needed for a framing project. Knowing the board foot formula and stud spacing calculations is essential.

Paint Calculator

Gallons for the coats you are actually putting on, after doors and windows come out.

Gallons = (wall area − openings) ÷ coverage per gallon × coats

How much does a gallon of paint cover?

A gallon of paint typically covers 350-400 square feet on a smooth, pre-primed surface. Textured surfaces, bare drywall, or porous materials may reduce coverage to 200-300 square feet per gallon. Always check the manufacturer label for specific coverage rates.

How many coats of paint do I need?

Most interior painting jobs require 2 coats for even coverage and full color development. You may need only 1 coat when painting the same color or using paint-and-primer combos. Dark or vivid colors may require 3 coats, especially over light-colored walls.

Is interior paint coverage different from exterior?

Yes. Exterior paint coverage is typically lower (250-350 sq ft/gallon) because exterior surfaces are usually rougher and more porous. Wood siding, stucco, and brick all absorb more paint than smooth interior drywall.

How do I account for doors and windows?

A standard interior door is approximately 20 square feet, and an average window is about 15 square feet. Subtract these from your total wall area before calculating paint needed. For large picture windows or French doors, measure the actual opening.

Should I buy extra paint?

Yes. Buy 10-15% more than calculated to account for touch-ups, waste, and coverage variations. Keep leftover paint stored properly for future touch-ups. Paint colors can be difficult to match exactly later, even with the same formula.

Tile Calculator

Tile count, grout and thinset for a floor or a wall, at the waste factor the layout needs.

Tiles = area × (1 + waste) ÷ area of one tile

How many tiles do I need per square foot?

It depends on tile size. For 12×12 tiles, you need approximately 1 tile per square foot. For 6×24 plank tiles, you need about 1 tile per square foot as well (since 6×24 = 144 sq in = 1 sq ft). Smaller tiles like 4×12 require about 3 tiles per square foot.

How much waste should I add for tile?

A standard waste factor is 10% for most installations. Use 15% for diagonal layouts or rooms with many cuts. For expensive tile, you might use 5-7% if you are an experienced installer.

How much grout do I need?

Grout requirements depend on tile size and grout joint width. As a general rule, plan for about 1 pound of grout per square foot for standard 12×12 tiles with 1/8" joints. Smaller tiles or wider joints require more grout.

How many bags of thinset do I need?

A 50-pound bag of thinset mortar typically covers about 50 square feet when applied with a 1/4" × 1/4" square-notch trowel. Larger tiles require a larger trowel (1/2" × 1/2"), reducing coverage to about 40 sq ft per bag.

What is the best tile size for a small bathroom?

For small bathrooms, 12×24 or 12×12 tiles work well as they create fewer grout lines, making the space feel larger. Avoid very large tiles (24×24) in tight spaces because they require more cuts and can look disproportionate.

Flooring Calculator

Boxes of plank or laminate for a room, with the waste a diagonal run costs you.

Boxes = area × (1 + waste) ÷ coverage per box

How much extra flooring should I buy?

The recommended waste factor varies by flooring type: hardwood 10%, laminate 8%, vinyl plank 5%, tile 10%, and carpet 10%. For diagonal installations or rooms with many angles, add an extra 5%.

How many boxes of laminate flooring do I need?

Most laminate flooring boxes cover 20-24 square feet. Divide your total square footage (including waste) by the sq ft per box listed on the packaging. For a 200 sq ft room with 8% waste, you need 216 sq ft / 24 = 9 boxes.

Do I need underlayment for all flooring types?

Underlayment is recommended for hardwood, laminate, and carpet. Most vinyl plank (LVP) products have built-in underlayment and do not need a separate layer. Tile uses thinset mortar directly on the subfloor or backer board.

How do I calculate flooring for an irregularly shaped room?

Break the room into rectangles, calculate each area separately, then add them together. For L-shaped rooms, divide into two rectangles. Always measure the longest dimensions to ensure you have enough material.

What is the most cost-effective flooring type?

Vinyl plank (LVP) is often the most cost-effective at $2-6 per sq ft installed. Laminate is similar at $2-5 per sq ft. Carpet varies widely ($2-8). Hardwood is the most expensive at $6-12+ per sq ft but adds the most resale value.

Brick Calculator

Bricks and mortar for a wall, by brick size and joint width.

Bricks = wall area × bricks per sq ft for the size and joint × (1 + waste)

How many bricks do I need per square foot?

For standard modular bricks (8×3.625×2.25 in) with 3/8" mortar joints, you need approximately 6.75 bricks per square foot. For 8×8×16 CMU blocks, you need about 1.125 blocks per square foot.

How much mortar do I need for brick or block?

For CMU blocks, plan for approximately 7 bags (60 lb) of mortar per 100 square feet of wall area. Standard bricks require more mortar — about 10.5 bags per 100 square feet due to more joints.

What is a standard CMU block size?

The most common CMU (Concrete Masonry Unit) is 8×8×16 inches nominal. The actual dimensions are 7-5/8×7-5/8×15-5/8 inches, accounting for the mortar joint. CMU also comes in 4, 6, 10, and 12-inch widths.

How much waste should I add for brick or block?

A standard waste factor is 5% for straight walls and 10% for walls with many cuts, curves, or patterns. Always order extra — it is far cheaper than a second delivery charge for a shortage.

What is the difference between a brick and a CMU block?

Bricks are smaller clay units (standard 8×3.625×2.25 in) fired in a kiln, while CMU (Concrete Masonry Units) are larger concrete blocks (typically 8×8×16 in). CMU walls go up faster but bricks offer more aesthetic options.

Gravel Calculator

Cubic yards and tons of aggregate for a driveway or a base course.

Cubic yards = length (ft) × width (ft) × depth (ft) ÷ 27; tons = yards × density

How many tons of gravel do I need?

First calculate cubic yards: (Length x Width x Depth in ft) / 27. Then multiply by the material weight in tons per cubic yard. Gravel weighs about 1.4 tons per cubic yard (2,800 lbs). For example, a 50 x 20 ft area at 4 inches deep = 12.35 cu yd x 1.4 = 17.3 tons.

How much does a cubic yard of gravel weigh?

Weight varies by material: gravel ~2,800 lbs (1.4 tons), sand ~2,700 lbs (1.35 tons), crushed stone ~2,600 lbs (1.3 tons), topsoil ~2,200 lbs (1.1 tons), fill dirt ~2,000 lbs (1.0 ton). Wet material can weigh 20-30% more.

How much gravel fits in a dump truck?

A standard single-axle dump truck holds about 10 cubic yards. A tandem (double-axle) dump truck holds 12-14 cubic yards. A tri-axle can carry up to 16-18 cubic yards. However, weight limits may reduce capacity for heavier materials.

Should I order extra gravel for compaction?

Yes. Loose gravel and fill materials compact by 15-20% when vibrated or driven over. Order 10-15% extra material to account for compaction. Crushed stone compacts more than round gravel.

How deep should a gravel driveway be?

A typical gravel driveway needs 4-6 inches of gravel over a compacted base. The base layer should be 4 inches of larger crushed stone (#57 or #67), topped with 2-3 inches of finer gravel (#21A or screenings) for a smooth driving surface.

Rebar Calculator

Bar count, total length and tie wire for a mat at a given spacing.

Bars per direction = (span ÷ spacing) + 1; total length = bars × run

How do I calculate rebar spacing?

Rebar spacing is measured center-to-center (on center, or o.c.). To find the number of bars in one direction, divide the slab dimension (in inches) by the spacing, then add 1. For example, a 30-ft slab at 12" o.c. = (30×12)/12 + 1 = 31 bars in that direction.

What is the standard rebar overlap?

The standard minimum lap splice (overlap) for rebar is 40 times the bar diameter. For #4 rebar (0.5" diameter), that is 40 × 0.5 = 20 inches. For #5 rebar (0.625"), it is 25 inches. Always check your project specifications, as some require longer laps.

What size rebar should I use for a concrete slab?

For a standard 4-inch residential slab, #3 or #4 rebar at 12-18" o.c. is typical. For driveways and heavier loads, use #4 at 12" o.c. For structural slabs and footings, #5 or #6 rebar is common. Always follow the structural engineer's specifications.

How much does rebar weigh per foot?

Rebar weight varies by size: #3 = 0.376 lb/ft, #4 = 0.668 lb/ft, #5 = 1.043 lb/ft, #6 = 1.502 lb/ft, #7 = 2.044 lb/ft, #8 = 2.670 lb/ft. A standard 20-ft #4 bar weighs about 13.4 pounds.

What does "on center" (o.c.) mean for rebar?

On center (o.c.) means the spacing is measured from the center of one bar to the center of the next. When plans call for "#4 @ 12" o.c. E.W." (each way), it means #4 rebar spaced every 12 inches in both directions, forming a grid.

Square Footage Calculator

Area for rooms of any shape, added up, with openings taken back out.

Area = length × width per rectangle, summed, less openings

On the exam this sits under Plan reading and estimating.

How do I calculate square footage?

For a rectangle, multiply length by width (both in feet) to get square feet. For a triangle, multiply base by height and divide by 2. For a circle, multiply pi (3.14159) by the radius squared. For a trapezoid, add the two parallel sides, divide by 2, and multiply by the height.

How do I convert square feet to square yards?

Divide the square footage by 9 to convert to square yards. There are 9 square feet in 1 square yard (3 ft x 3 ft = 9 sq ft). For example, 270 sq ft = 30 sq yd. This conversion is commonly used for carpet and flooring.

How do I calculate square footage for irregular shapes?

Break the irregular shape into simpler shapes (rectangles, triangles, circles). Calculate the area of each part separately, then add them together. Our multi-room mode lets you calculate and sum multiple shapes. For L-shaped rooms, split into two rectangles.

How many square feet are in an acre?

One acre equals 43,560 square feet. A standard American football field (excluding end zones) is about 48,000 square feet, or roughly 1.1 acres. An acre is also equal to 4,840 square yards or approximately 4,047 square meters.

How do I measure square footage of a room?

Measure the length and width of the room in feet using a tape measure. Multiply length by width. For rooms with closets or alcoves, measure the main rectangle first, then measure and add each additional section. Subtract any built-in fixtures if needed.

Roof Slope Calculator

Pitch, angle and slope factor from a rise and run, both ways.

Slope factor = √(rise² + 12²) ÷ 12, for a rise stated per 12 inches of run

On the exam this sits under Plan reading.

How do I calculate slope percentage (grade)?

Slope percentage = (Rise / Run) x 100. For example, if the ground rises 2 feet over a 50-foot run, the grade is (2/50) x 100 = 4%. Grade is the most common way to express slope in construction.

What is the ADA ramp slope requirement?

The ADA requires a maximum slope of 1:12 (8.33%) for ramps. This means for every 1 inch of rise, you need at least 12 inches of run. The maximum rise per section is 30 inches, with landings at the top and bottom.

What slope is needed for proper drainage?

For surface drainage away from buildings, a minimum slope of 1-2% (1/8" to 1/4" per foot) is recommended. The IRC requires a minimum 6-inch drop in the first 10 feet from the foundation (5% grade).

How do I convert slope to roof pitch?

Roof pitch is expressed as rise per 12 inches of run. To convert from slope percentage: Pitch = (Grade% / 100) x 12. For example, a 33.3% grade = (33.3/100) x 12 = 4/12 pitch.

What is the maximum driveway slope?

Most building codes limit driveways to a maximum slope of 15-20% (about 8.5-11.3 degrees). The recommended slope is 2-5% for comfortable driving and drainage. Steeper driveways may require heating systems in cold climates.

Stair Calculator

Riser and tread that land inside code from a total rise, with the stringer length.

Risers = total rise ÷ target riser, rounded; tread from 2 × riser + tread = 24–25 in

On the exam this sits under Building codes.

What is the maximum riser height per IRC code?

The International Residential Code (IRC R311.7.5.1) limits maximum riser height to 7-3/4 inches (7.75"). Individual risers within a stairway must not vary more than 3/8" from the tallest to the shortest.

What is the minimum tread depth per code?

The IRC requires a minimum tread depth of 10 inches, measured horizontally from nosing to nosing. This ensures safe footing when descending stairs.

How do I calculate the number of risers?

Divide the total rise (floor-to-floor height in inches) by the target riser height (7" is ideal). Round to the nearest whole number. Then divide the total rise by the number of risers to get the exact riser height.

What is the stair builder rule of thumb?

The comfort rule states that riser height + tread depth should equal 17 to 18 inches. For example, a 7" riser with a 10.5" tread = 17.5", which is in the comfort zone.

How long should stair stringers be?

Stringer length is calculated using the Pythagorean theorem: sqrt(total rise² + total run²). For a 9-ft floor-to-floor height with 10" treads, the total run is approximately 12.5 ft and the stringer length is about 15.4 ft.

Markup and Margin Calculator

The difference between a 20% markup and a 20% margin, which is where bids get lost.

Price = cost ÷ (1 − margin); markup % = (price − cost) ÷ cost

On the exam this sits under Business and finance.

What is the difference between markup and margin?

Markup is the percentage added to cost to arrive at selling price: Markup = (Price - Cost) / Cost x 100. Margin is the percentage of selling price that is profit: Margin = (Price - Cost) / Price x 100. A 50% markup equals a 33.33% margin. Markup is always a higher number than margin for the same dollar profit.

What is a typical contractor markup?

Most general contractors use a markup of 10-20% for large commercial projects and 25-50% for residential remodeling. Specialty subcontractors may use markups of 15-35%. The markup must cover overhead and profit — a 20% markup yields only a 16.67% profit margin.

How do I price construction jobs correctly?

Start by calculating all direct costs (labor, materials, equipment, subcontractors). Add overhead as a percentage (typically 10-20% of direct costs), then add your desired profit margin. Use the formula: Selling Price = Total Cost / (1 - Desired Margin%). For example, if costs are $100,000 and you want a 15% margin: $100,000 / (1 - 0.15) = $117,647.

Why do contractors confuse markup and margin?

Many contractors say "I add 20% markup" but actually mean a 20% margin. This mistake costs real money: a 20% markup on $100,000 costs yields $120,000 revenue ($20,000 profit), while a 20% margin yields $125,000 revenue ($25,000 profit). The FL contractor exam tests your ability to distinguish these concepts.

Does the FL contractor exam test markup vs margin?

Yes. The Business & Financial Management portion of the Florida General Contractor exam includes questions on pricing, cost estimation, and profit calculation. You need to know how to convert between markup and margin and apply the correct formula depending on what the question asks.

Hourly Rate Calculator

What you have to charge an hour once overhead, unbillable time and profit are in it.

Rate = (annual overhead + wage + target profit) ÷ billable hours a year

On the exam this sits under Business and finance.

What should a contractor charge per hour?

A contractor's hourly rate depends on trade, location, experience, and overhead costs. In Florida, general contractors typically charge $50-$100/hour, while specialty trades (electrical, plumbing) charge $75-$150/hour. Your rate must cover your salary, labor burden (payroll taxes and benefits), overhead, and profit. Use the calculator above to determine your specific rate.

What is labor burden rate?

Labor burden is the true cost of employing someone beyond their base wage. It includes employer payroll taxes (FICA 7.65%, FUTA, SUTA), workers compensation insurance, health insurance, paid time off, and other benefits. Typical labor burden rates range from 25-40% of base wages. A worker earning $25/hour may actually cost the employer $32-$35/hour.

What is the difference between billable and total hours?

Billable hours are the hours you can charge to clients for productive work. Total hours include non-billable time: estimating, travel, marketing, administration, training, and downtime. Most contractors have 1,200-1,600 billable hours per year out of 2,080 total working hours. Using total hours instead of billable hours to calculate your rate will result in under-charging.

How do I account for overhead in my hourly rate?

Overhead includes all business costs not directly tied to a project: office rent, insurance, vehicle costs, tools, licenses, accounting, marketing, and administrative staff. Calculate your total annual overhead, then express it as a percentage of your direct labor costs. Typical overhead rates range from 15-30% for small contractors.

Does the FL contractor exam cover labor rate calculations?

Yes. The Business & Financial Management portion of the Florida General Contractor exam tests your understanding of labor costs, burden rates, overhead allocation, and pricing strategies. You need to know how to calculate the fully-loaded cost of labor and build that into bids and hourly rates.