Knackpad

Drawing Scale Calculator

Convert drawn measurements ↔ real-world dimensions · find implied scale · scale areas & volumes. All units, all scales, instant results.

Common Scales
1 :
Enter a drawn length and scale ratio above
1 :
Enter a real-world dimension and scale ratio above

Know a drawn length and its real counterpart? Enter both to find the implied scale ratio.

Enter both lengths above to find the scale

Scale areas and volumes using the same ratio. Areas scale by N², volumes by N³.

1 :
Enter a scaled value and scale ratio above

How it works

A drawing scale is written as 1 : N. The denominator N tells you how many real-world units equal one drawing unit. All unit conversions happen internally via millimetres.

Real from drawn Real = Drawn × N
Drawn from real Drawn = Real ÷ N
Implied scale N = Realmm ÷ Drawnmm
Area scaling Real area = Drawn area × N²
Example: A 50 mm line on a 1:100 plan → 50 × 100 = 5,000 mm = 5 m in the real world. The same room on a 1:50 plan would need a 100 mm line.

Common scales reference

Scale 1 mm on drawing = Typical use
1:11 mm realFull-size details, machine parts
1:22 mm realSmall mechanical details
1:55 mm realConstruction details, joinery
1:1010 mm = 1 cmStructural details, sections
1:2020 mm = 2 cmInterior elevations
1:5050 mm = 5 cmFloor plans (detailed), sections
1:100100 mm = 0.1 mFloor plans (standard), elevations
1:200200 mm = 0.2 mSite layouts, larger buildings
1:500500 mm = 0.5 mSite plans, master plans
1:10001 m realUrban blocks, large sites
1:12501.25 m realOrdnance survey maps (UK)
1:25002.5 m realLarge area survey maps
1:50005 m realRegional planning, topography
1:1000010 m realTown/city mapping

Frequently asked questions

What does a scale of 1:50 mean?
Every 1 unit on the drawing equals 50 of the same units in reality. So 1 mm on paper = 50 mm (5 cm) in real life. A 200 mm line on a 1:50 drawing represents a 10,000 mm (10 m) wall. It is the standard scale for detailed architectural floor plans and interior layouts.
How do I find the scale of a drawing I don't know?
Find a feature whose real-world size you already know — a standard door is typically 900 mm wide, a parking space is about 2,400 mm × 4,800 mm, or look for a dimension already labelled on the drawing. Measure it on paper, then use the Find Scale tab: N = real ÷ drawn. If 15 mm on paper represents a 900 mm door, the scale is 1:60.
Can I mix metric and imperial units?
Yes. Select your measurement unit for the drawn length and a different unit for the output. This calculator converts everything internally via millimetres, so you can measure in inches on a ruler and get a result in metres, or vice versa.
How do I scale an area or volume from a drawing?
Linear scale is 1:N, but area scales by N² and volume by N³. Use the Area / Vol tab. For example, a 25 cm² room on a 1:100 plan represents 25 × 100² = 250,000 cm² = 25 m² in reality. Volume works the same way: multiply by N³.
What is the difference between 1:100 and 1:50?
At 1:100, every millimetre on paper equals 100 mm (10 cm) in the real world — a 50 mm drawing length means 5 m. At 1:50 the same 50 mm drawing length only represents 2.5 m. Larger scale denominators compress more real-world distance into the same drawing space, making objects appear smaller.
What scales do architects and engineers use?
Architecture: 1:50 (detailed plans), 1:100 (general floor plans), 1:200 and 1:500 (site plans). Civil/structural drawings often use 1:1250, 1:2500, 1:5000. Mechanical engineering details work at 1:1, 1:2, 1:5, or 1:10. Ordnance Survey maps use 1:1250 (large scale urban) through 1:250,000 (regional).