A detail drawing shows a wall section at a scale of 1/2" = 1'-0". If a dimension measures 3 inches on the drawing, what is the actual dimension?
Correct Answer
A) 6 feet
At 1/2" = 1'-0" scale, each 1/2 inch on the drawing equals 12 inches actual. Therefore, 3 inches on the drawing equals 3 ÷ 0.5 = 6 feet actual dimension.
Why This Is the Correct Answer
At a scale of 1/2" = 1'-0", every half inch on the drawing represents one foot in reality. To find the actual dimension, divide the drawing measurement by the scale factor: 3 inches ÷ 0.5 inches = 6. Since each unit represents 1 foot, the actual dimension is 6 feet. This scale conversion is fundamental in construction plan reading.
Why the Other Options Are Wrong
Option B: 3 feet
This answer incorrectly assumes a 1:1 ratio between drawing inches and actual feet. At 1/2" = 1'-0" scale, 3 inches on the drawing doesn't equal 3 feet actual. The correct calculation requires dividing by the scale factor (0.5) to get 6 feet, not simply converting inches to feet.
Option C: 18 inches
This answer fails to apply the scale conversion entirely. It treats the 3-inch drawing measurement as if it were already the actual dimension. The scale of 1/2" = 1'-0" means the drawing is reduced, so the actual dimension must be larger than the drawing measurement.
Option D: 36 inches
This answer incorrectly multiplies instead of dividing by the scale factor. While 36 inches equals 3 feet, this calculation (3 × 12 = 36) ignores the scale entirely. The proper method is to divide the drawing measurement by 0.5, then convert to the appropriate units.
Memory Technique
Remember 'Half-Scale Doubles': When the scale shows 1/2 inch equals 1 foot, divide the drawing measurement by 0.5 to double it for the actual size.
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