Architectural Scale Converter

Convert a measurement off a drawing into a real-world dimension at any imperial, engineering or metric scale — and back. Work out what a set becomes when it is reprinted at a different sheet size, and pull the CAD scale factor, viewport zoom and text height for every architectural scale. One ratio underlies all of it; this tool keeps the arithmetic honest so you can trust the number.
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Every Scale Is One Ratio

An architectural scale is nothing more than a ratio between paper and the world. When we write ¼″ = 1′-0″ we are saying that a quarter inch on the sheet stands for one foot — twelve inches — in reality. Divide twelve by a quarter and you get forty-eight: one drawing unit equals forty-eight real units, a ratio of 1:48. That single number does all the work.

Paper → real: multiply the measured length by the ratio. Three inches on a 1:48 drawing is 3 × 48 = 144 inches, or 12′-0″.

Real → paper: divide by the ratio. A 30-foot wall on that same drawing plots at 360 ÷ 48 = 7½ inches.

Reprinted at a new size: every dimension on the sheet is multiplied by the zoom percentage, so the scale designation itself changes. A ¼″=1′-0″ drawing copied to 50% becomes ⅛″=1′-0″.

In CAD: the ratio is the scale factor — the value you give DIMSCALE and LTSCALE, and the multiplier for model-space text and blocks. The same scale plots in a layout viewport at 1 divided by the factor, expressed as an xp zoom.

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Scale Factor Reference

The scale factor is the ratio's denominator — the multiplier between the drawing and the real world. Architect's scales use a fraction of an inch to a foot; engineer's scales use one inch to a round number of feet.

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Frequently Asked Questions

‍What is the scale factor for ¼″ = 1′-0″?
48. One foot is twelve inches, and a quarter inch goes into twelve forty-eight times, giving a 1:48 ratio. Use 48 for DIMSCALE and LTSCALE; the viewport plots at 1/48xp.

‍How do I convert a measured length to real size?
Multiply by the ratio. A 3″ line at 1:48 is 3 × 48 = 144″ = 12′-0″. The Paper ↔ Real tab does it for any scale and reverses it.

‍My drawing printed at the wrong size — what scale is it now?
Reprinting multiplies every dimension by the zoom. A ¼″ set at 50% reads as ⅛″. The Reprint tab gives the exact percentage between any two scales.

‍What is a CAD scale factor?
The model-to-paper ratio — 48 for ¼″, 96 for ⅛″. It sets DIMSCALE, LTSCALE and text height: 1/8″ plotted text is 48 × 1/8″ = 6″ in model space at ¼″.

‍Architect's vs engineer's scale?
Architect's uses a fraction of an inch to the foot (buildings); engineer's uses one inch to a round number of feet (site and civil). Both are ratios and both are handled here, along with metric.