Scale Calculator

How to use the scale calculator

1. Choose what to find. For a length conversion, enter the scale as drawing or model A to real B, then enter the known length and select its unit.
2. To find a scale, enter the drawing or model length and the corresponding real length, each with its own unit. Both must be positive measurements of the same feature.
3. Read the labelled result. You can change the result unit or open Calculation details. Changing tasks starts fresh; Clear resets the current task.

Read the ratio in the right direction

At 1:100, one drawing unit represents 100 of the same units in reality. A 2:1 drawing is twice real size. Scale is unitless; length-unit conversion is handled separately.

Real length is drawing length × B ÷ A. Drawing length is real length × A ÷ B. To find scale, convert matching lengths to the same unit and compare drawing to real.

Positive results show up to six significant digits and tiny nonzero values stay visible. Length conversions allow zero. Found scales normalize one side to 1; they are approximate measurements, not exact reduced fractions or certification of the whole drawing.

Drawing, model and map examples

At 1:100, a 5 cm line represents 5 m. A real 4.2 m wall at 1:50 measures 8.4 cm on a drawing. Check which value you are finding.

A 5 cm model feature representing 2.5 m gives about 1:50. A 6-inch model of a 3-inch part gives about 2:1, an enlargement.

On a uniformly scaled 1:25000 map, 4 cm represents 1 km. This is linear scale arithmetic, not a terrain, route, projection or travel-distance calculation.

What the result does not verify

Resizing, zooming, scanning and fit-to-page printing can change physical scale. Check a trustworthy matching dimension on the actual representation. One reference does not prove uniform scale in every direction or part.

Only lengths are converted. Areas and volumes have different scale factors. No files are inspected, changed or printed. Use decimal measurements, not compound feet-and-inches or architectural fractions. Changing an input unit reinterprets the retained number.

Your measurements

Arithmetic runs in your browser. This tool adds no measurement upload, saved record or input-bearing URL. Existing website consent, analytics and network services remain separate.