Architectural Scale Converter
Drawing scale to real size at any imperial, engineering or metric scale, answered in feet-inches to the nearest 1/16 inch with the rounding residual shown.
Type into either field — the other follows. Imperial output is written the way it goes on a drawing, to the nearest 1/16", and the rounding it applied is shown.
Quick answer: what one inch on the drawing is on site
| Scale | Ratio | 1 inch on paper | 1 m on site, on paper |
|---|---|---|---|
| 1" = 1'-0" | 1:12 | 1'-0" | 83.3 mm |
| 3/4" = 1'-0" | 1:16 | 1'-4" | 62.5 mm |
| 1/2" = 1'-0" | 1:24 | 2'-0" | 41.7 mm |
| 3/8" = 1'-0" | 1:32 | 2'-8" | 31.2 mm |
| 1/4" = 1'-0" | 1:48 | 4'-0" | 20.8 mm |
| 3/16" = 1'-0" | 1:64 | 5'-4" | 15.6 mm |
| 1/8" = 1'-0" | 1:96 | 8'-0" | 10.4 mm |
| 1" = 20' | 1:240 | 20'-0" | 4.2 mm |
At 1/4" = 1'-0" every inch on the sheet is 4 feet on site. A printed PDF at the wrong paper size changes every one of these; measure the graphic scale bar before trusting a dimension.
| Scale factor | — |
|---|---|
| Real size — imperial | — |
| Real size — metric | — |
| 1 drawing inch equals | — |
| 1 drawing mm equals | — |
A "half size" print on 11×17 is only half size if the original was ANSI D. ANSI D is 22×34 and halves exactly onto ANSI B, 11×17 (ASME Y14.1). ARCH D is 24×36 and halves onto ARCH B, 12×18. That is an architectural trade size, not an ASME one, and it is not in the office copier. So ARCH D gets fitted to 11×17 instead, and the binding ratio is 11/24, not 1/2: the image lands at 11 × 16.5 in, 91.7% of half size. A 1/4" = 1'-0" plan reduced that way reads 45'-10" on the 1/8" edge where the building is 50'-0". Everything taken off the sheet is 8.3% short, and fit to page fits the printable area, so it is smaller again.
1:48 is not 1:50. The imperial and metric scales in the list above sit 25/24 apart, exactly 4.17%. That is 1:48 against 1:50, and 1:96 against 1:100. Lay a 1:50 edge on a 1:48 drawing and a 30.48 m wall reads 31.75 m: 100'-0" read as 104'-2". That is a small enough error to pass a glance, so read the scale block on the sheet before you pick up a rule.
Even a print that meets spec is not a dimension. HP rates the DesignJet T850 at ±0.1% of the specified vector length or ±0.2 mm (whichever greater), and only at 23°C, 50–60% relative humidity, on coated roll stock. Over a 36 in run that is 0.036 in. At 1:48 that is 1.7 in of real building, out of a plotter in a conditioned room. Paper moves after that. Do not scale is a drawing note, not a contract term. The word does not appear anywhere in AIA A201–2017, and what §3.2.2 requires instead is that the contractor take field measurements of any existing conditions. With no figured dimension and nobody to ask, use the graphic scale bar. It was plotted with the drawing and shrank with it. HABS §5.7.2 requires a pair of scale bars, English and the corresponding metric scale, for every scale used on a sheet.
ANSI D halves exactly; ARCH D does not. The City of San Diego's CADD standard (2018) lists the ANSI sheets as A 8.5 × 11, B 11 × 17, C 17 × 22, D 22 × 34 and E 34 × 44 in., and each one is the next folded in half. A D sheet printed on B is exactly half size and every scale on it is exactly half: 1/4" = 1'-0" reads as 1/8". ARCH D, 24 × 36, has no office-paper half, which is the 11/24 problem worked out above.
Half size is designed for, not tolerated. The same standard tells drafters to pick scales that stay legible when the drawing is reduced to half size, and sets the smallest lettering on a full-size D sheet at 1/8 in. Printed at half size that lettering is 1/16 in.; lines and lettering have to be heavy enough to survive it.
A profile carries two scales on purpose. For plan and profile drawings the standard requires a 1:10 ratio between vertical and horizontal: 1 in. = 4 ft vertical with 1 in. = 40 ft horizontal, or 1 in. = 10 ft with 1 in. = 100 ft. A slope read off a profile with one rule is wrong by a factor of ten. A sheet that is not to scale says No Scale in its title block; NTS belongs only on a specific dimension. It is a city standard for the city's own drawings, quoted here because it writes down what most offices only assume.
What I check on a job
The figured dimension I scale first. Before I trust a number off a sheet, I find a figured dimension on the same drawing, a grid spacing or an overall, and scale that first. If the converter returns what is written, the print is at its stated scale. If it does not, I stop believing the scale note and work out the real ratio from the two numbers: the written length in inches divided by what I measured in inches, typed into the custom field. That check catches the reduced set, the PDF fitted to a screen, and the detail placed at the wrong scale. I repeat it for each drawing, because a plan and an enlarged detail on one sheet are two scales, and a title-block scale may speak for only one. The output is rounded to a sixteenth of building, but my rule reads to a sixteenth of paper, and at 1/4" = 1'-0" that is 3 inches of building, so a scaled length is a range, not a dimension.
Imperial architectural scales are the ratio of drawn length to real length: 1/4" = 1'-0" means 0.25 in stands for 12 in, i.e. 1:48. Engineering scales are 1 in to a whole number of feet.
Worked example
A wall measures 3½ inches on a drawing at ¼" = 1'-0". How long is it really?
- ¼" = 1'-0" means 1 inch on paper is 48 inches built: the factor is 48.
- 3.5 in × 48 = 168 in.
- 168 in ÷ 12 = 14 ft.
The wall is 14'-0" (4.27 m). At that scale every 1/16 inch of pencil is 3 inches of building, which is why the residual line matters.
4 values on this page were driven in a browser and compared with independently derived figures on 2026-10-29 (2808 values across 228 calculators site-wide).
Questions
What does ¼" = 1'-0" mean as a ratio?
1:48. One inch on the drawing is 48 inches built; ⅛" = 1'-0" is 1:96, ½" = 1'-0" is 1:24.
Why does the converter show a rounding residual?
Because a drawn length rarely lands exactly on a sixteenth. The residual is the part left over after rounding to the nearest 1/16 inch, so you can see how much the tape and the drawing disagree.
Does it handle engineering and metric scales?
Yes: 1" = 20' style engineering scales and 1:50, 1:100 metric scales, all converted through their exact factors.
Why is a half-size print of an ARCH D sheet not half size?
ARCH D is 24 × 36 and halves to 12 × 18, a size office copiers do not have. Fitted to 11 × 17 the ratio is 11/24: the image is 91.7% of half size, so a 1/4" plan reads 45'-10" on the 1/8" edge where the building is 50'-0".
How far apart are 1:48 and 1:50?
Exactly 25/24, 4.17%. A 100'-0" (30.48 m) wall drawn at 1:48 reads 104'-2" (31.75 m) with a 1:50 rule. Read the scale block before picking up a rule.