CalculateSite

Drawings, maps & models

Scale Converter

Find an actual length, a drawing or model length, or the scale between them. Use different units on each side without converting them by hand.

Convert a scale or length

Scale: drawing or model (A) : actual (B)

At 1 : 50, one unit on the drawing represents 50 of the same unit in actual size. Use 2 : 1 for a drawing twice actual size.

Enter positive numbers with a period for decimals. Grouped values such as 50,000 are accepted. Select length units from the menus; enter the two scale numbers separately.

Example: 5 cm at 1 : 50,000 → 2.5 km.

Actual length

Enter the known length and scale, then select Calculate.

≈ marks display rounding. This is a linear length conversion. Calculations run in your browser. Press Enter to calculate. Successful results appear in this tab's Recent calculations.

Three worked examples

Find actual length

A 5 cm line on a map

5 × 50,000 = 250,000 cm

At a uniform 1 : 50,000 scale, 5 cm represents 2.5 km. The scale uses the same unit on both sides; the final centimeters are then converted to kilometers.

Find drawing length

A 4.2 m wall at 1 : 50

4.2 m ÷ 50 = 0.084 m

The wall's drawing length is 8.4 cm. Enter 4.2 m as the actual length, use A = 1 and B = 50, and choose cm for the result.

Find scale ratio

A 6 in model of a 3 in part

6 in : 3 in = 2 : 1

The model is an enlargement at 2 : 1. Its equivalent normalized ratio is 1 : 0.5: one inch on the model represents half an inch on the actual part.

Formula, units, and calculation rules

Let D be drawing or model length and L be actual length, expressed in the same unit. At a scale A : B, D/L = A/B. Therefore L = D × B/A and D = L × A/B. When both lengths are known, the calculator converts them to meters and reduces D : L to an exact integer ratio.

All inputs must be positive. The calculator accepts up to 15 digits before the decimal point and 10 after it, within 64 characters. Intermediate values are exact fractions; rounding happens only for display. Halfway values round away from zero. Trailing decimal zeros are omitted, and ≈ identifies a rounded number or normalized ratio. The integer ratio stays exact for the entered values.

Units use exact definitions: 1 in = 0.0254 m, 1 ft = 0.3048 m, 1 yd = 0.9144 m, and 1 mi = 1,609.344 m. These are international units, not legacy U.S. survey feet or survey miles. Unit conversion does not improve the accuracy of a ruler, survey, or original drawing.

This tool applies a uniform linear scale. It does not measure anything on your screen, compensate for resized images, or correct a map projection. Map scale can vary with position or direction; use an appropriate local scale when that variation matters. Actual length here is the length represented by the supplied scale, not automatically a road route or terrain-following distance.

References: USGS: Map Scales for the relationship between map and actual distances; NIST: SI Units — Length and NIST: revised unit conversion factors for length definitions. See our calculation policy for shared rules.

Common questions

Can I enter inches on one side and feet on the other?

Yes. Choose each length's unit separately. For example, a 1 in drawing length and a 2 ft actual length produce a 1 : 24 scale, because 2 ft is 24 in.

What does a scale such as 1 : 50 mean?

One length unit on the drawing corresponds to 50 of that same unit in actual size. For example, 1 cm represents 50 cm, and 1 in represents 50 in. The ratio itself has no unit.

Why can a normalized ratio be 1 : 0.5?

Normalization sets the drawing side to one. If the drawing is twice actual size, 2 : 1 becomes 1 : 0.5. Both ratios describe the same enlargement. The exact integer ratio is shown alongside it.

Does a 1 : 10 scale also divide area by 10?

No. It divides each corresponding length by 10. For geometrically similar shapes, area changes by the square of the length factor and volume by its cube. This converter calculates lengths only.

Can I measure a drawing directly on my monitor?

The calculator does not calibrate your display. Zoom, device scaling, and image resizing can change physical dimensions on screen. Use a known reference length or verify the current printed scale before entering a measurement.

Why does a positive length display as ≈ 0?

The chosen decimal precision cannot show that small value. Increase the decimal places or choose a smaller result unit. The unrounded calculation and exact integer ratio are retained.