Map scale calculator
Measure a distance on a map with a ruler and enter the scale printed on it, such as 1:25,000 or 1:24,000. The calculator converts it to the real distance on the ground – or tells you how long a route will be on the map, or what the scale is when you know both lengths.
Runs in your browser: nothing you enter is sent anywhere.
How to use it
- Choose what to find: the ground distance, the map distance or the scale.
- Choose centimetres and kilometres or inches and miles.
- Enter the two known values. The scale is the number after “1 :” printed on the map.
With a scale of 1 : N and both distances in the same unit:
- ground distance = map distance × N
- map distance = ground distance ÷ N
- N = ground distance ÷ map distance
1 km = 100,000 cm; 1 mile = 63,360 inches; 1 foot = 12 inches.
Worked examples
Map to ground. On a 1:25,000 hiking map a path measures 4 cm. 4 × 25,000 = 100,000 cm = 1 km. On this map 1 cm = 250 m.
Ground to map. On a 1:50,000 map, 2.5 km = 250,000 cm becomes 250,000 ÷ 50,000 = 5 cm.
Scale. 3 inches on the map cover 1.5 miles = 95,040 inches: 95,040 ÷ 3 = 1:31,680.
Common mistakes
- Mixing units: the scale only works when both distances are in the same unit – that is why the calculator converts to centimetres or inches first.
- Reading a scale bar as a ratio: a bar that says “1 km” is not a scale of 1:1,000. Measure the bar with a ruler and use the “scale” mode to get the ratio.
- Photocopies and screens: enlarging or shrinking a printed map changes its ratio but not the printed “1:N”. A scale bar stays right.
Frequently asked questions
What does a scale of 1:25,000 mean?
One unit on the map is 25,000 of the same units on the ground. 1 cm on the map is 25,000 cm = 250 m, so 4 cm is 1 km. The bigger the number after the colon, the more ground fits on the sheet and the less detail it shows.
How do I find the scale of a map?
Measure the map distance between two points whose real distance you know (for example from a road sign or a distance tool), then divide the ground distance by the map distance in the same unit. 6 cm on the map for 3 km = 300,000 cm gives 300,000 ÷ 6 = 1:50,000.
What is the scale of US topographic maps?
The classic USGS 7.5-minute quadrangles are 1:24,000: 1 inch on the map is 24,000 inches = 2,000 feet, and 2.64 inches is one mile.
Can I measure a curved route?
Yes – lay a string along the route on the map, straighten it and measure it with a ruler, or add up short straight pieces. Then enter that length as the map distance.
Does the scale apply everywhere on the map?
On large-scale maps of a small area (1:10,000 to 1:100,000) practically yes. On maps of a whole country or the world the projection stretches distances, and the printed scale is exact only along certain lines.