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What does this converter do?
Multiply the drawing length by the scale ratio. A 12 cm wall on a 1:50 blueprint represents 12 × 50 = 600 cm, which is 6.00 m at full size.
How the scale converter works
A drawing scale is written as 1:N, where N is the ratio between paper and reality. Every unit you measure on the plan stands for N of those units in the real world, so the conversion is a single multiplication: real length = measured length × N. A 5 cm line on a 1:200 site plan equals 5 × 200 = 1,000 cm, or 10 m.
Enter the ratio as the number after the colon, type the length you measured, and pick centimeters or meters. The result is shown in meters, so centimeter measurements are divided by 100 at the end. A 4.2 cm room on a 1:100 plan gives 4.2 × 100 = 420 cm, reported as 4.20 m.
Common scales for plans, sites, and maps
Architectural drawings cluster around a few standard ratios. Detail drawings use 1:5, 1:10, or 1:20, floor plans use 1:50 or 1:100, and long elevations may drop to 1:200. On a 1:100 plan, 1 cm on paper is 1 m in the building, which makes mental checks quick.
Site plans usually sit between 1:200 and 1:500, and maps go far higher, with 1:25,000 and 1:50,000 common for hiking maps. A scale ruler marked with these ratios lets you read real dimensions directly. To convert the other way, from a real size to a paper size, divide by the ratio instead of multiplying.
How this calculator works
Formula
Multiply the length you measure on the drawing by the scale ratio to get the real size. A 1:N scale means 1 unit on paper equals N of the same units in reality. If you measured in centimeters, the result is divided by 100 to show meters.
Worked example
A room measures 4.2 cm on a 1:100 floor plan. Real size = 4.2 × 100 = 420 cm = 4.20 m.
Assumptions to verify
- The ratio is the denominator of a 1:N scale, so a 1:100 plan uses ratio 100.
- The measured length is a straight-line distance on the drawing, entered in centimeters or meters.
- The drawing is printed at its stated scale; enlarging, shrinking, or photocopying it invalidates the ratio.
Frequently asked questions
What does a scale of 1:100 mean?
One unit on the drawing equals 100 of the same units in real life. A 1 cm line on a 1:100 plan represents 100 cm, or 1 m, at full size.
How do I read a measurement from a 1:50 blueprint?
Multiply the length you measure by 50. A 9 cm pipe run on a 1:50 drawing is 9 × 50 = 450 cm, or 4.50 m in reality.
Which scales do plans, site plans, and maps use?
Detailed building plans commonly use 1:20 to 1:100, site plans use 1:200 to 1:500, and maps use 1:25,000 or larger ratios such as 1:50,000.
Cite this tool
BoringToolsKit. “Scale Converter.” boringtoolskit.com/scale-converter/. Free to reference in articles, syllabi, and answer posts with a link.
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