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Scale Calculator

Convert between real and scaled lengths for drawings, maps and models. Find the ratio from two measurements. Rebase between scales.

Architectural

Model

Map

Scale ratio (1 : N)

Rebase: I have a length already drawn at one scale, output it at another scale

From scale (1 : N)

To scale (1 : N)

Real length

Result

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Calculation details

Working steps will appear here once you enter values.

FAQ

What does a scale ratio like 1:100 mean?: 1 unit on the drawing equals 100 units in reality. A line 30 mm long on a 1:100 plan represents 3000 mm (3 m) on site. The unit on both sides of the ratio is always the same.
Which scale should I use for an architectural plan?: Site plans usually go on 1:500 or 1:1000. Building plans, sections and elevations typically use 1:100 or 1:50. Detail drawings use 1:20, 1:10 or 1:5. Pick the scale that lets the drawing fit the sheet while keeping critical dimensions readable.
How do I rebase a drawing from 1:100 to 1:50?: Switch on the "Rebase" toggle in the first tab. A line that was 30 mm at 1:100 (representing 3000 mm in reality) becomes 60 mm at 1:50 — the drawing doubles, the building stays the same.
How do model scales like 1:24, 1:35 and 1:72 compare?: The bigger the second number, the smaller the model. A car 4.5 m long is 188 mm at 1:24, 129 mm at 1:35, 63 mm at 1:72. Pick the model tab preset and enter the real length to see the model dimensions.
My map says 1:25000. How many real metres in 1 cm?: Use the "Scaled → Real" tab with ratio 25000 and a length of 1 cm — you get 250 m. For 1 cm at 1:50000 the answer is 500 m, at 1:100000 it is 1 km.

A scale ratio relates a length on a drawing, map or model to the same length in reality. The same calculator covers all three workflows. Architects switch between 1:50 plans, 1:100 elevations and 1:500 site plans. A modeller builds a kit at 1:24, 1:35 or 1:72 and needs to know whether a 4.5 m car becomes 188 mm or 63 mm. A walker reading a 1:25000 OS map needs the real distance behind 8 cm of trail. The tool also reverses the question: enter a real length and the matching distance you measured on a drawing, get the ratio plus the nearest standard scale. A rebase mode rescales an existing drawing from one ratio to another so the same line at 1:100 becomes the right length at 1:50 for a detail view. Results appear in mm, cm, m, km and inches, feet and miles at once.