How to use it
Fill in any two of the first three boxes and the third is worked out.
- Scale and On drawing give the actual size: measure 3 5/8" on a 1/4" scale drawing and read the real dimension.
- Scale and Actual give the length to draw.
- On drawing and Actual give the scale, which is how to work out the scale of a print that has been reduced or has no scale noted.
The scale can be typed as 1/4" = 1'-0", as just 1/4, as an engineering scale such as 1" = 20', or as a ratio such as 1:48 or 1:100.
Worked examples
- At 1/4" = 1'-0", one inch on the drawing is 4 feet, so 3 5/8" on the drawing is 14' 6" in the building.
- A wall known to be 18' long measures 2 1/4" on a print. 18' is 216 inches, and 216 ÷ 2.25 = 96, so the print is at 1:96, which is 1/8" = 1'-0".
Architectural scales
| Scale | Ratio | 1" on the drawing is |
|---|---|---|
| 3" = 1'-0" | 1:4 | 4" |
| 1 1/2" = 1'-0" | 1:8 | 8" |
| 1" = 1'-0" | 1:12 | 1' 0" |
| 3/4" = 1'-0" | 1:16 | 1' 4" |
| 1/2" = 1'-0" | 1:24 | 2' 0" |
| 3/8" = 1'-0" | 1:32 | 2' 8" |
| 1/4" = 1'-0" | 1:48 | 4' 0" |
| 3/16" = 1'-0" | 1:64 | 5' 4" |
| 1/8" = 1'-0" | 1:96 | 8' 0" |
| 3/32" = 1'-0" | 1:128 | 10' 8" |
| 1/16" = 1'-0" | 1:192 | 16' 0" |
Engineering scales
| Scale | Ratio |
|---|---|
| 1" = 10' | 1:120 |
| 1" = 20' | 1:240 |
| 1" = 30' | 1:360 |
| 1" = 40' | 1:480 |
| 1" = 50' | 1:600 |
| 1" = 60' | 1:720 |
Typing measurements
Every box takes feet, inches and fractions the way you would write them: 9' 1 1/8", 7 1/2", 2.5' or 300mm. Put a space between whole inches and a fraction. A box also takes a whole calculation, so 14' 6" / 2 works anywhere.
Questions
What is 1/4 inch scale as a ratio?
1/4" = 1'-0" is 1:48. A foot is 12 inches, and 12 ÷ 1/4 is 48, so everything is drawn at one forty-eighth of its real size.
How do I find the scale of a drawing?
Find something on it whose real size you know, such as a door or a dimensioned wall, and measure it on the paper. Divide the real size by the measured size, both in inches. Enter the two lengths in On drawing and Actual and the calculator names the scale.
How do I convert a drawing from 1/8 scale to 1/4 scale?
Print or copy it at 200%. Going the other way, from 1/4 to 1/8, is 50%. For any other pair, divide the ratio of the old scale by the ratio of the new one: 96 ÷ 48 = 2, which is 200%.
What is the difference between an architectural and an engineering scale?
An architectural scale gives a fraction of an inch to the foot, such as 1/4" = 1'-0". An engineering scale gives a whole number of feet to the inch, such as 1" = 20', which is 1:240.
More calculators
- Feet & inches calculatorAdd, subtract, multiply and divide feet, inches and fractions. Free, nothing to install.
- Decimal feet to feet & inches converterType a length in any one box: decimal feet, feet and inches, inches or millimeters. The other three fill in.
- Roof pitch & rafter length calculatorEnter any two of pitch, rise, run and diagonal. The other two fill in.
- Stair calculatorEnter the floor-to-floor rise to get risers, treads, total run and stringer length.
- Circle & arc calculatorEnter a diameter for circumference and area. Add an angle for arc length and chord.
- Square footage & volume calculatorEnter length and width for area. Add a height for volume, cubic yards and wall area.
- Stud & on-center spacing calculatorEnter a length and a spacing to get the member count, the last bay and the equal spacing.
- Concrete calculatorPick slab, footing, wall or round column, type the size in feet and inches, and get cubic yards and bags.
- Slope converterType a slope as inches per foot, percent, degrees or a ratio. The other three fill in.
- Gravel, sand, soil & mulch calculatorPick the material, type the length, width and depth, and get cubic yards and approximate tons.
Reference finders
- DSA forms & publications finderType a topic or a number, or paste a plan check comment, and see which DSA documents to open.
- OSHPD / HCAI CAN, PIN & forms finderType a topic or a number, or paste a plan review comment, and see which HCAI documents to open.