Drawing Scale Converter
Convert scaled drawing sizes to real sizes and find a scale.
What does a drawing scale mean?
Architectural and engineering drawings are drawn smaller than the real building so that they fit on paper. The scale tells you how much smaller. A scale of 1:100 means that 1 unit on the drawing equals 100 of the same units in real life, so 10 mm on the plan is 1,000 mm, or 1 m, on site. Imperial drawings often write the scale as a statement such as 1/4″ = 1′-0″, which means a quarter of an inch on paper represents one foot. This converter handles both styles.
How to use the scale converter
- Choose metric or imperial units, then pick the drawing scale. Choose Custom if your scale is not listed.
- On the Drawing to real tab, type the length you measured with a ruler and pick its unit. The real size appears instantly in your chosen unit, along with a table of other units.
- On the Real to drawing tab, type a real length to find out how long to draw it.
- On the Find the scale tab, enter a length measured on the drawing and the real length it represents, such as a door you know is 900 mm wide. The tool calculates the scale and shows the nearest standard scales.
Scales included
- Metric ratio scales from 1:1 through 1:5, 1:10, 1:20, 1:50, 1:100, 1:200 and 1:500 up to 1:5000.
- Architectural scales from 3″ = 1′-0″ down to 1/16″ = 1′-0″, including the common 1/4″ and 1/8″ scales.
- Engineering scales such as 1″ = 10′, 1″ = 20′ and 1″ = 100′ for site plans.
- Units: millimetres, centimetres, metres, inches and feet, with feet-inches input such as 12′ 6″.
When you need it
Use the converter when you have a printed plan but no scale ruler, when you need to draw a piece of furniture to the same scale as a floor plan, or when you are checking a PDF that was printed at a different paper size. Model makers use it to scale real objects down, and students use it to check homework on technical drawing.
Tips
A drawing printed on a different paper size than it was made for is no longer at its stated scale. A sheet drawn for A1 and printed on A3 is half size, so a 1:100 plan becomes 1:200. Always check a known dimension or the scale bar with the Find the scale tab before relying on measurements. Written dimensions on a drawing always take priority over measuring it with a ruler.
Frequently asked questions
What scale is 1/4 inch to 1 foot?
A quarter inch to one foot is a ratio of 1:48, because one foot is 12 inches and 12 divided by 0.25 is 48. One eighth of an inch to one foot is 1:96.
How do I find the scale of a drawing?
Measure something on the drawing whose real size you know, such as a standard door or a written dimension. Enter both lengths on the Find the scale tab and the tool calculates the ratio and the nearest standard scale.
Are the converted sizes exact?
The maths is exact for the scale you choose, but results are estimates because your ruler reading, paper shrinkage and printer resizing all add error. Use written dimensions where they exist.