Free · No sign-up · Runs in your browser
Scale any drawing
to any ratio
The modern replacement for the eidograph: a free scale calculator for drafters, architects, model makers and map readers — with guides to the antique instrument itself.
Scale calculator
Enter your original drawing size and target scale — get the enlarged or reduced dimensions instantly. Everything runs in your browser.
A 420 × 297 mm drawing scaled at 1:2 becomes 210 × 148.5 mm.
How it works
Measure the original
Enter the width and height of your drawing, plan, or photo. Any unit works — mm and cm for drafting, inches for imperial plans, px for screens.
Pick the target scale
Choose a ratio like 1:2 or 3:4, type any custom ratio, or work in percentages — 50% for half size, 200% for double.
Read the scaled size
You get the exact enlarged or reduced dimensions, the percentage change, and the simplified ratio — instantly, right in your browser.
Common drawing scales
Quick reference — the calculator handles all of these and any custom ratio.
| Full-size detail drawings | 1:1 |
|---|---|
| General component drawings | 1:2 |
| Large assemblies, site plans | 1:20 · 1:50 · 1:100 |
| Enlarged small parts | 2:1 · 5:1 · 10:1 |
| US architectural (imperial) | 1/4" = 1'-0" (1:48) |
| Fractional reductions | 3:4 · 2:3 · 5:8 |
What is an eidograph?
A Victorian-era drawing instrument that scales drawings up and down using parallel brass arms and sliding weights — the refined successor of the pantograph. Learn how it worked and why a calculator does the job today.
Read the guideCollecting antique instruments
Drafting sets from makers like W. & S. Jones, Stanley, and Keuffel & Esser are a quiet, affordable corner of tool collecting. Start with what to look for, what to avoid, and how sets are priced.
Collecting guideFrequently asked questions
What does a scale of 1:2 mean?
A scale of 1:2 means every 1 unit on the new drawing equals 2 units on the original — the drawing is reduced to half its width and height. A scale of 2:1 works the other way: the drawing is drawn twice as large.
How do I convert a percentage to a ratio?
Divide the percentage by 100 and simplify. 50% becomes 1:2, 75% becomes 3:4, and 150% becomes 3:2. The calculator shows this simplified ratio automatically when you use the percentage mode.
Does scaling change the aspect ratio?
No. Applying one scale factor to both width and height keeps the proportions identical — a 3:4 landscape drawing scaled to any ratio stays a 3:4 landscape. If you need a different shape, scale each side separately.
Is this the same as an eidograph?
An eidograph is a mechanical instrument that achieves the same result with pivoted brass arms and sliding weights. This calculator is its digital replacement: enter any ratio, get exact dimensions — no arms to balance.