How do I convert a 1:100 plan measurement to metres?

Multiply the millimetres on paper by 100, then divide by 1000. So 1 mm is 0.1 m and 63 mm is 6.3 m. At 1:50, 1 mm is 0.05 m; at 1:200, 0.2 m.

What happens if I print an A1 plan on A3?

Everything shrinks to about half (A3's long side is 420 mm against A1's 841 mm), so a 1:100 drawing measures at 1:200. The title block still says 1:100, so measure a written dimension to check.

How do I find the scale of a plan?

Find a dimension written on the plan, measure it on the printed sheet, then divide the real length in millimetres by the paper length. 6,300 mm measuring 63 mm gives 1:100.

How much area does an A3 sheet at 1:100 cover?

42 × 29.7 m of site. At 1:50 it's 21 × 14.85 m, and at 1:200 it's 84 × 59.4 m.

Free calculator

Plan scale calculator

Real length = paper length × the scale number. At 1:100, 1 mm on paper is 100 mm (0.1 m) on site, so 63 mm measures 6.3 m. An A1 drawing printed on A3 halves: 1:100 becomes 1:200.

Your job

What do you want to know?

On the paper

Drawing scale

Other scale 1 :

Paper

Drawn for

Printed on

A sizes share one shape, so each step down halves the area and scales lengths by about 0.71.

The sheet is drawn to its true shape. The scale bar reads in real metres at the scale it's printed at.

Real length

6.30m

63.0 mm on paper at 1:100

A3 sheet covers

42.0m

by 29.7 m at 1:100

1 mm on paper

0.10m

1 m real is 10.00 mm on paper

The working, with your numbers

1. Real length63.0 mm × 100 ÷ 1000= 6.300 m
2. Sheet covers420 × 297 mm × 100 ÷ 1000= 42.0 × 29.7 m

Typed those measurements in by hand?MetreMate measures them straight off your PDF plans. Free to start.

The formula, in plain words

1Real length (m) = paper length (mm) × N ÷ 1000, for a drawing at 1:N.
2Paper length (mm) = real length (m) × 1000 ÷ N.
3Scale from a known dimension: N = real length (m) × 1000 ÷ measured paper length (mm).
4Printed on a different A size: N as printed = N × the drawn sheet's long side ÷ the printed sheet's long side. A1 (841 mm) on A3 (420 mm) doubles N.
5A sheet covers its size × N: an A3 sheet (420 × 297 mm) at 1:100 covers 42 × 29.7 m.

Worked example

An A3 plan at 1:100. A wall measures 63 mm with a ruler, and the same plan was also printed from an A1 original.

1.Real length: 63 mm × 100 ÷ 1000 = 6.3 m.
2.The A3 sheet covers 420 × 100 ÷ 1000 = 42 m by 29.7 m of site.
3.An A1 drawing at 1:100 printed on A3: 100 × 841 ÷ 420 = 200.2, so it measures at about 1:200, and the same 63 mm is about 12.6 m.

Answer: 6.3 m at 1:100; about 12.6 m if it's an A1 drawing printed on A3.

How to measure it

Read the scale and sheet size from the title block, e.g. 1:100 @ A1.
Check what size you've actually printed on: a resized print changes the scale.
Measure along a written dimension first to check the scale before measuring the rest.
Use a ruler in millimetres, or a scale rule set to the drawing's scale.

Where the numbers come from

Every default in the calculator is a number a supplier or manufacturer publishes. We list the source next to it so you can check.

What	Value	Source
A-series paper (mm): A0 841 × 1189, A1 594 × 841, A2 420 × 594, A3 297 × 420, A4 210 × 297	420 mm (A3 long side)	Markus Kuhn, University of Cambridge, International standard paper sizes (ISO 216) (checked 2026-10-01)

Manufacturers named here are the source of the number, not a recommendation. Confirm quantities with your supplier.

Frequently asked questions

Stop typing measurements in by hand

MetreMate measures every wall, floor and roof straight off your PDF plan. Then it hands you the same numbers this calculator asks for.

Try MetreMate free