Blueprint Scale Calculator
Turn a measurement taken off a scaled drawing into the real-world dimension (or back) for any blueprint scale.
How it works
Real = drawing measurement × scale · Drawing = real ÷ scale
On a 1:n blueprint, every unit measured on the paper represents n units of the actual structure, so you multiply the measured length by n to recover the real size. This works for any consistent scale — 1:50 and 1:100 are common in architecture, 1:20 for details. Keep both sides in the same unit; the scale itself is a pure number with no units attached.
Worked example
On a 1:50 floor plan, a wall that measures 12 cm on the drawing is 12 × 50 = 600 cm, or 6 metres, in reality. To draw a real 4-metre (400 cm) wall on the same plan you’d put down 400 ÷ 50 = 8 cm.
Sources: Scale (ratio) — Wikipedia
Frequently asked questions
What is the difference between 1:50 and 1:100?
A 1:50 drawing is twice as large as a 1:100 drawing of the same object, so it shows more detail. On 1:100, a 6-metre wall is 6 cm; on 1:50 the same wall is 12 cm.
Can I use this for imperial scales like 1/4" = 1′?
Convert the architectural scale to a ratio first. 1/4 inch = 1 foot is 1:48 (because 1 foot = 12 inches, and 12 ÷ 0.25 = 48). Then enter 48 as the scale.
Does the scale affect angles?
No. Scaling changes all lengths by the same factor, so angles and shapes are preserved. A 30° corner on the drawing is still 30° in the finished build.
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This calculator is for educational purposes. Double-check important results before acting on them.