This map scale calculator converts between the distance you measure on a map or drawing and the distance it represents on the ground. Enter a measurement and its scale — 1:500 for a site plan, 1:50 000 for a topographic sheet — and get the real world distance, or work the other way to find how long a known ground distance should be drawn.
Enter the scale denominator only: type 500 for a 1:500 drawing, 50000 for a 1:50 000 map.
How much ground one unit on the map represents, for the scales that appear most often on plans and topographic sheets.
| Scale | 1 mm on map | 1 cm on map | 1 inch on map |
|---|---|---|---|
| 1:100 | 0.1 m | 1 m | 2.5 m |
| 1:200 | 0.2 m | 2 m | 5.1 m |
| 1:250 | 0.25 m | 2.5 m | 6.4 m |
| 1:500 | 0.5 m | 5 m | 12.7 m |
| 1:1,000 | 1 m | 10 m | 25.4 m |
| 1:1,250 | 1.25 m | 12.5 m | 31.8 m |
| 1:2,500 | 2.5 m | 25 m | 63.5 m |
| 1:5,000 | 5 m | 50 m | 127 m |
| 1:10,000 | 10 m | 100 m | 254 m |
| 1:24,000 | 24 m | 240 m | 609.6 m |
| 1:25,000 | 25 m | 250 m | 635 m |
| 1:50,000 | 50 m | 500 m | 1,270 m |
| 1:63,360 | 63.36 m | 633.6 m | 1,609 m |
| 1:100,000 | 100 m | 1 km | 2,540 m |
| 1:250,000 | 250 m | 2.5 km | 6,350 m |
A map scale is a ratio. On a 1:500 drawing, one unit measured on the paper represents 500 of the same units on the ground, so 1 mm on the drawing is 500 mm — half a metre — on site. The scale is dimensionless, which is why a 1:50 000 map works the same whether the map is printed in metric or imperial units: measure in millimetres and the answer comes out in millimetres, then convert.
To go from map to ground, multiply the measured distance by the scale denominator and convert the units. To go from ground to map, divide instead. Finding an unknown scale is the same relationship rearranged: divide the ground distance by the measured map distance, after both have been converted to the same unit, and round to the nearest convenient ratio.
One practical caution. The scale printed on a drawing only holds for a full-size print. If a PDF or a photocopy has been scaled to fit a page, every measurement taken from the paper is wrong by the same factor — which is exactly what the “find the scale” tab is for. Check the printed scale bar against a known dimension before you trust any measurement.
A representative fraction is a scale written as a ratio with no unit attached, as in 1:24 000. Because it is a pure fraction it works in any unit: 1 mm on the map is 24 000 mm on the ground, and 1 inch on the map is 24 000 inches on the ground. A representative fraction calculator therefore needs nothing more than the ratio itself, which is why the scale box above asks only for the denominator.
The scale factor is the same number turned into a multiplier. Going from map to ground the scale factor is the denominator, so on a 1:24 000 sheet you multiply by 24 000; going from ground to map the scale factor is its reciprocal, 1 ÷ 24 000. Keeping those two directions straight is the usual source of error with a scale factor calculator, so decide which way round you are working before you start.
Three ratios turn up again and again on published maps: 1:24 000, the classic USGS 7.5-minute quadrangle; 1:50 000, the standard topographic sheet across much of the world; and 1:63 360, the old one-inch-to-one-mile series, in which one inch on the paper is exactly one mile on the ground.
An architectural scale converter does the same job for drawings dimensioned in feet and inches rather than as a plain ratio. On an architectural drawing the scale is stated as a fraction of an inch to one foot — 1/4 inch to 1 foot means a quarter of an inch on the paper represents one foot on the building. Familiar variants are 1/8 inch, 3/16 inch, 1/2 inch and 1 inch to the foot, each of which corresponds to a ratio that this page handles directly.
Converting between the two notations is a single division. At 1/4 inch to 1 foot, one inch on the paper represents four feet, or 48 inches, so the equivalent ratio is 1:48. In the same way 1/8 inch to 1 foot is 1:96, and 1 inch to 1 foot is 1:12. Enter the ratio in the map-to-ground tab and the architectural measurement is converted with no extra tool.
Do not confuse the two families. An architect's scale is a fraction of an inch to the foot and is dimensionless once converted; an engineer's scale is a decimal division such as 1:100 or 1:2 500 and appears on civil and survey drawings. Both are handled here, but the ruler has to match the drawing.
Scale conversions come up whenever paper and ground have to agree — most often in these situations:
Multiply the distance measured on the map by the scale denominator, then convert units. On a 1:500 drawing, 63.5 mm measured on the paper represents 63.5 times 500 millimetres on the ground, which is 31,750 mm or 31.75 m. On a 1:50 000 map, 8 mm represents 400 m.
It means that one unit on the drawing equals 500 of the same units on the ground. So 1 mm on the drawing is 500 mm, or 0.5 m, on site; 1 cm on the drawing is 5 m; and a 20 mm line on the paper represents a 10 m distance in the real world.
Measure a feature whose real size you know, such as a boundary or a building frontage, then divide the ground distance by the map distance once both are in the same unit. If 8 mm on the paper corresponds to 400 m on the ground, the ratio is 400 divided by 0.008, which is 50,000, so the drawing is at 1:50 000.
Most PDF plans and scanned maps are printed to fit the page, which changes the printed size and therefore the effective scale. The printed scale bar can also drift during copying. Measure a known dimension first and use the find-the-scale tab to recover the true factor before doing any other measurement.
No, and the two are easily confused. A map scale is the paper to ground ratio — 1:2,500, for example. A scale factor is a projection parameter, such as UTM's 0.9996, which describes how much a map projection distorts distance at a particular place. A measurement taken from a map combines both effects.
Yes, it is free with no login and no usage limit, and the arithmetic runs entirely in your browser.
Calculations run locally in your browser. Verify critical values against your project's coordinate reference system and specification before use in the field. About · Privacy & cookies · Terms of use · Developers