FastTool

MEASURE · MODEL · MAKE

Scale calculator.
Get the dimensions right.

From a room plan to a miniature: convert real dimensions, reverse a model measurement, or find the exact resize percentage between two scales.

  • Metric + imperial
  • Reduction + enlargement
  • No upload or account

THE WORKBENCH

Set the scale. See the size.

Calculated in your browser
Try an example
01

Your dimensions

Scale

Model : real. Use 1:100 for a smaller model, or 2:1 for double actual size.

Real-world dimensions

Use decimal points, not commas or fractions. Each row can use a different unit. Leave optional dimensions blank.

Loading calculator…

02

Your result

A clear answer, in your units.

The room example is ready to calculate. Enter your own measurements or choose an example above.

THE METHOD, NOT A BLACK BOX

Three jobs. One consistent rule.

01 / REAL → MODEL

Turn a real size into a model.

A scale is always written model : real. Convert the length into one unit, then multiply by the model side divided by the real side.

Model = real × (A ÷ B)

At 1:100, a 12 m room becomes 12,000 mm ÷ 100 = 120 mm. At 2:1, an 18 mm part becomes 36 mm.

02 / MODEL → REAL

Read a dimension from a model.

Divide the measured model dimension by its model-to-real ratio. The output unit can differ from the measurement unit.

Real = model ÷ (A ÷ B)

A 120 mm measurement at 1:100 represents 12,000 mm, or 12 m. A 36 mm measurement at 2:1 represents 18 mm.

03 / SCALE → SCALE

Resize a drawing or model.

Divide the target model-to-real ratio by the current one. Multiply by 100 for the final size percentage in a uniform resize operation.

Resize % = (target ÷ current) × 100

From 1:100 to 1:50: (1 ÷ 50) ÷ (1 ÷ 100) = 2×, or 200%. Each length doubles; area is 4× and volume is 8×.

Before you print or fabricate

  • Confirm whether the original drawing has already been resized. A printed scale label cannot detect this for you.
  • Use uniform scaling and the same units in your CAD or slicer. “Fit to page” can apply another, unwanted size change.
  • Check a known dimension on the finished print or model. The screen diagram is a comparison, not a calibrated ruler.
  • No CAD, mesh or PDF files are opened or modified. This does not check strength, accuracy, tolerances or printer limits.

Units, precision & privacy

The inch is exactly 25.4 mm; the international foot is exactly 304.8 mm. Historical U.S. survey feet are not supported. See NIST: SI units of length and NIST: foot conversion factors.

Positive inputs from 10−9 to 1012; scale ratios and length changes from 10−9× to 109×. Calculations use JavaScript floating-point numbers, with no arbitrary-precision guarantee.

Measurements stay in this tab. This calculator does not upload, store or include your dimensions in share links. Copying and downloading happen only when you choose them.

Common scale questions

Is 1:50 larger or smaller than 1:100?

For the same real object, a 1:50 model has twice the length of a 1:100 model. The denominator is smaller, so the model is larger.

Does 200% mean a 200% increase?

No. A final size of 200% means twice the original length, which is a 100% increase. This calculator reports the final size percentage used by resize controls.

Can I enter feet and inches, or fractions?

Choose ft or in for the dimension and enter a decimal number. For 5 ft 6 in, use 5.5 ft or 66 in. For 3/8 in, use 0.375 in. Separate dimensions can use different units.

Will doubling a 3D print use eight times the material?

Only the volume of a uniformly scaled solid shape follows the cube rule directly. Actual printed material also depends on wall thickness, infill, supports and slicing choices. Use your slicer for a print estimate.