What does 1/4" = 1'-0" mean?

Every 1/4 in on the drawing stands for 1 ft in the building, a ratio of 1:48. It is the typical scale for residential floor plans; 1/8" = 1'-0" (1:96) is used for larger buildings.

What is an engineer scale?

A scale in whole feet per inch, used on site and civil sheets: 1" = 10', 20', 30', 40', 50' or 60'. 1" = 20' is a ratio of 1:240.

Is an 11 x 17 print of a 24 x 36 sheet half scale?

No. 11 / 24 = 0.458 and 17 / 36 = 0.472, so fit to page is roughly 46 percent, not 50. A true half-size set of ARCH D is 12 x 18 (ARCH B), where 1/4" scale reads as 1/8".

What sheet sizes do plans come on?

ARCH C is 18 x 24 in, ARCH D 24 x 36 in, ARCH E1 30 x 42 in and ARCH E 36 x 48 in. Tabloid is 11 x 17 in.

Is a scaled measurement accurate enough to bid from?

Only as accurate as the print. Check a known dimension first, and use written dimensions where the drawings give them.

Free calculator

Architect scale calculator

Real feet = inches on the paper x the scale ratio / 12. At 1/4" = 1'-0" (1:48), 3.5 in on the sheet is 3.5 x 48 / 12 = 14 ft.

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Measured on paper

Scale

Drawing scale

Sheets

Drawn on

Printed on

The printed sheet to scale. A dashed outline shows the sheet it was drawn for.

Real length

14.00ft

14'-0"

Scale ratio

48(1:N)

1/4" = 1'-0"

Sheet covers

144ft

by 96 ft on ARCH D

The working, with your numbers

1. Scale ratio1/4" = 1'-0"= 1:48
2. Real length3.500 x 48.0 / 12= 14.00 ft

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The formula, in plain words

1Scale ratio: 1/4" = 1'-0" means 1/4 in on paper stands for 12 in, so the ratio is 12 / 0.25 = 48 (1:48). 1/8" = 1'-0" is 1:96.
2Engineer scales: 1" = 20' is 1 in for 240 in, so 1:240.
3Real feet = inches measured on the paper times the ratio, divided by 12.
4Inches on paper = real feet times 12, divided by the ratio.
5Printed smaller (fit to page), the ratio grows: divide it by the shrink (11 x 17 from ARCH D is 11 / 24 = 0.458).

Worked example

A wall measures 3.5 in on an ARCH D floor plan drawn at 1/4" = 1'-0". Then the same sheet printed to fit 11 x 17.

1.Ratio: 12 / 0.25 = 48.
2.Real length: 3.5 x 48 / 12 = 14 ft.
3.Shrink to 11 x 17: 11 / 24 = 0.458 (17 / 36 = 0.472, the smaller one wins).
4.On the print the wall measures 3.5 x 0.458 = 1.60 in, and the true scale is 48 / 0.458 = about 1:105.
5.Read with a 1/4 in scale ruler it would wrongly come out 1.60 x 48 / 12 = 6.4 ft.

Answer: 14 ft at 1/4" = 1'-0". On an 11 x 17 print of the same sheet the scale is about 1:105, so calibrate off a known dimension.

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How to measure it

Find the scale in the title block or under each drawing title. Details on one sheet often use a different scale from the plan.
Measure on the paper in inches, or read a dimension you know (a door, a grid line) to check the print.
If the set was printed smaller than it was drawn (half-size or fit to 11 x 17), set the printed sheet so the calculator corrects the ratio.

Where the numbers come from

Every default in the calculator comes from a published source. We list the source next to it so you can check.

What	Value	Source
Architect scales: 1/4" = 1'-0" (1:48) for typical floor plans, 1/8" = 1'-0" (1:96) for larger buildings	48 (1/4" = 1'-0" is 1:48)	U.S. Fire Administration, engineer and architect scales (checked 2026-09-20)
Engineer scales for site and civil sheets: 1" = 10', 20', 30', 40', 50' and 60'	240 (1" = 20' is 1:240)	Archtoolbox, CAD scale factors (checked 2026-09-20)
ARCH sheets: C 18 x 24 in, D 24 x 36 in, E1 30 x 42 in, E 36 x 48 in; tabloid 11 x 17 in	36 in (ARCH D long side)	Archtoolbox, paper sizes (checked 2026-09-20)

Manufacturers named here are the source of the number, not a recommendation. Confirm quantities with your supplier.

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