Drawing Scale Converter

Convert a measurement from one drawing scale to another, work out the real size behind a drawn length, or find the scale you need to fit a drawing on a given sheet. Works with metric ratios such as 1:50 and 1:100, imperial architect's scales such as 1/4" = 1'-0", and enlargement scales such as 2:1 and 5:1.

On this page: Convert · Real size · Fit to sheet · Scales · How to use · FAQ

Convert Between Two Drawing Scales

A detail drawn at one scale usually has to be redrawn at another. Enter the length as it is drawn now and the two scales.

Length as drawn

Current scale

New scale

Drawn Length to Real Size

Measure a line on the drawing and read the real-world dimension it stands for.

Measured on drawing

Drawing scale

Which Scale Fits My Sheet?

Enter the real size of the object and the sheet you are drawing on. The calculator shows the largest standard scale that still fits, with a 10 mm margin on each edge.

Real size — length width

Sheet

Standard Drawing Scales

Reduction scales (metric)

Scale	1 mm on paper	Typical use
1:5	5 mm	Joinery and component details
1:10	10 mm	Details, sections
1:20	20 mm	Room details, stairs
1:50	50 mm	Floor plans, elevations
1:100	100 mm	Whole-building plans
1:200	200 mm	Large buildings
1:500	500 mm	Site plans
1:1000	1 m	Site and location plans
1:1250 / 1:2500	1.25 m / 2.5 m	Location plans, land registry

Enlargement scales

Small components are drawn larger than life. 2:1 is twice real size, 5:1 five times, 10:1 ten times. The calculator accepts these as well; a measurement at 2:1 is half the real dimension of the part.

Imperial architect's scales

North American drawings use fractional inch notation. 1/4" = 1'-0" is the same as 1:48, and 1/8" = 1'-0" is 1:96. The full table is on the Architectural Scale Calculator.

How to Use the Drawing Scale Converter

To redraw a detail at a new scale, use the first calculator. Enter the length as it appears on the current drawing and pick both scales.
To read a dimension off a plan, use the second calculator with the scale printed in the title block.
To choose a scale before you start drawing, use the third calculator with the real size and your sheet.

Converting from a smaller denominator to a larger one reduces the drawing: 1:50 to 1:100 halves every length. Going the other way enlarges it.

Formula

new length = drawn length × new scale factor ÷ current scale factor

Here the scale factor is the denominator: 50 for 1:50. For an enlargement such as 2:1 the factor is 0.5, because the drawing is twice real size.

Example: a 120 mm detail at 1:50 redrawn at 1:20 becomes 120 × 50 ÷ 20 = 300 mm.

Drawing Scale Questions

What is a drawing scale?

A drawing scale is the fixed ratio between a length on the drawing and the matching length on the real object. A plan at 1:50 shows every dimension at one fiftieth of real size, so 20 mm on the sheet is one metre in the building.

How do I change a drawing from 1:50 to 1:100?

Halve every length. 1:100 has twice the denominator of 1:50, so the drawing is half as large. If you are rescaling a printed sheet, print it at 50 % — see the Print Scale Calculator.

Which scale should I choose for a floor plan?

1:50 for a single dwelling or apartment, 1:100 for a whole building, 1:200 for a large or multi-storey development. The third calculator on this page picks the largest standard scale that still fits your sheet.

What does a scale of 2:1 mean?

The drawing is twice the size of the real part. It is used for small components such as fixings and electronic parts. A 30 mm line on a 2:1 drawing is a real dimension of 15 mm.

Does the scale change if I resize the drawing?

Yes. Any enlargement or reduction, including printing with "fit to page", changes the effective scale and makes the printed ratio wrong. A graphic scale bar stays correct because it is resized along with the drawing.

Do drawing scales work the same in metric and imperial?

The arithmetic is identical; only the notation differs. Metric drawings state the ratio directly (1:50), while imperial drawings state an equivalence (1/4" = 1'-0") that corresponds to a ratio, in that case 1:48.