SuperDevTools
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Scale calculator for maps, plans and models

1. The scale

Type 1:25000, 1/50 or 25000. For an enlargement, type 2:1.

Plans
Maps
Models
Enlargement

2. The calculation

I want to find:
Result —

    3. Conversion table at %e%

    On the planIn reality
    In realityOn the plan

    4. Convert a graphic scale bar

    Measure the scale bar printed on the document with a ruler, then enter the distance written next to it.

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    The calculation runs in your browser. Your last values stay on this device.

    A scale calculator that handles the units for you

    A scale tells you how many times reality has been shrunk on paper. At 1:25,000, 1 cm on the map is 25,000 cm on the ground, which is 250 m. The maths is easy; losing a zero while converting centimetres to kilometres, or inches to miles, is easier. This scale conversion tool does all three calculations, with its own unit on each side: millimetres, centimetres, metres, kilometres, inches, feet or miles. Everything runs in your browser.

    How to use it

    1. In "Scale", type 1:25000, 1/50 or just 25000, or tap a button in the "Plans", "Maps", "Models" and "Enlargement" rows. For a drawing larger than the object, type 2:1.
    2. Under "I want to find:", pick "the real distance", "the length on the plan" or "the scale".
    3. Fill in "Length on the plan" and "Real distance" as needed and choose a "Unit" for each. The calculated box has a dashed border.
    4. Read the "Result" and the working below it, then press "Copy result" if you need it.

    The "Conversion table" block turns 1 mm, 1 cm, 5 cm or 1 m on the plan into real distances, and the other way round. It also suggests a "Scale bar to draw" about 5 cm (or 2 inches) long. The last block, "Convert a graphic scale bar", is for documents that only show a graduated bar.

    Worked examples

    • Walking map at 1:25,000: 4 cm × 25,000 = 100,000 cm = 1 km.
    • Architect's plan at 1:50: a 7 m wall is 700 cm ÷ 50 = 14 cm on the drawing.
    • Die-cast car at 1:43: a 4.3 m car is 430 cm ÷ 43 = 10 cm long.
    • US house plan at 1/4 inch = 1 foot: one foot is 12 inches, and 12 ÷ 0.25 = 48, so the scale is 1:48. Enter 0.25 in and 1 ft and choose "the scale".

    Working backwards is just as quick. On an old town map with no legend, 2.5 cm covers the 500 m between two junctions: 500 m = 50,000 cm, and 50,000 ÷ 2.5 = 20,000. The scale is 1:20,000. When the division is not a whole number, the tool shows both the "Rounded scale" and the "exact scale": a 3 cm bar labelled 1 km gives 1:33,333, exactly 1:33,333.333.

    Enlargement scales work too. At 2:1, a 12 mm screw is drawn 24 mm long.

    Common scales by use

    UseScale1 cm on paper is
    Joinery detail, small machine part1:10, 2:110 cm, 5 mm
    Room layout1:5050 cm
    House floor plans and elevations1:1001 m
    Site plan1:200, 1:5002 m, 5 m
    Walking map1:25,000250 m
    Regional map1:50,000, 1:100,000500 m, 1 km
    Model railway HO, N1:87, 1:16087 cm, 1.6 m
    Model cars1:43, 1:24, 1:1843 cm, 24 cm, 18 cm

    A common mix-up: a "large scale" map is 1:25,000 rather than 1:100,000. It shows things larger and in more detail, over a smaller area.

    FAQ

    How do I calculate a scale from two measurements?

    Put both lengths in the same unit, then divide the real distance by the length on the plan. The answer n gives the scale 1:n. Choose "the scale" under "I want to find:" and the unit conversion is done for you.

    How far is 1 inch on a 1:63,360 map?

    Exactly one mile, because a mile is 63,360 inches. On a 1:25,000 map, 1 inch is 635 m, or about 0.39 miles.

    My plan was photocopied at a smaller size. Is the scale still right?

    No. The written scale no longer applies, but a graduated bar shrinks with the drawing. Measure that bar, use "Convert a graphic scale bar", then press "Use this scale" to carry on with the new value.

    Can I mix inches and centimetres?

    Yes. Each side has its own "Unit". At 1:12, 1 inch on the model is 12 inches, which is 1 foot or 30.48 cm if you pick centimetres.