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Scale Factor Calculator

Compare a model with the real object, or two drawings, and get the scale factor, the percentage and the reciprocal.

Scale factor calculator

Scale factor: —
Scale percentage: —
Reciprocal: —
Scale ratio: —
—
The scale factor is the real size divided by the model size, so a factor of 8 means the real object is eight times larger.

How to use the Scale Factor Calculator

  1. Choose whether you are comparing a model with the real object or two drawings.
  2. Enter both lengths in the same units, model first and real size second.
  3. Read the scale factor, the percentage, the reciprocal and the ratio.

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Frequently Asked Questions

Common questions about the free online scale factor calculator.

Divide the real size by the model size. A 15 cm model of a 120 cm object gives a scale factor of 8, written as 1 to 8.
Scale factor equals the real measurement divided by the model measurement, so 120 divided by 15 is a factor of 8.
The reciprocal is one divided by the scale factor. It converts real sizes back into model sizes, so 1 divided by 8 is 0.125.
The percentage is the scale factor multiplied by 100. A factor of 8 is 800 percent, meaning the real object is eight times the model.
Pick the two drawing mode, then enter the length from each plan. The factor is the second length divided by the first.
One unit on the drawing equals 50 units in real life, so a 20 mm line on the plan stands for 1000 mm, which is one metre.
No. The scale factor is calculated locally in your browser, so the measurements you type are never sent to a server.
Yes. It is completely free, needs no account, and there is no limit on how many scale factors you work out.

Last updated: October 10, 2026