Map Scale Distance Converter
Measure a distance on your map, enter the map scale, and instantly see the real-world distance in kilometres, miles, metres, and nautical miles. Add multiple legs for a full route total with estimated walking time. Nothing uploaded.
Map Scale
Mode
OS map guide
- 1:10,000 - Street detail, surveying
- 1:25,000 - Explorer: footpaths, field boundaries
- 1:50,000 - Landranger: long routes, cycling
- 1:100,000 - Road planning, overview
- 1:250,000 - Regional / road atlas
Route Legs
| # | Map dist (mm) | Ascent (m) ? | Real distance |
|---|
Route Totals
Real World - Map
Learn more: map scale math and walking time estimates
Map distance to real distance
A scale of 1:25,000 means 1 mm on the map is 25,000 mm on the ground, which is 25 m. The tool multiplies your measured map distance in millimetres by the scale number, then converts the result to metres, kilometres, miles and nautical miles.
On a 1:25,000 map, 4 cm is 1 km on the ground. The same 4 cm on a 1:50,000 map is 2 km, because the larger number means each centimetre covers more ground. A 1:25,000 map shows less area per sheet but more detail than a 1:100,000 map.
Naismith's rule
Wikipedia's article on Naismith's rule says William W. Naismith, a Scottish mountaineer, formulated it in 1892: allow one hour for every three miles on the map and an additional hour per 2,000 feet of ascent. The metric version is one hour per 5 km forward plus one hour per 600 m of ascent.
The tool uses 5 km/h plus 1 minute per 10 m of ascent. For 10 km with 400 m of climbing, that is 120 minutes for the distance and 40 for the climb, so 2 hours 40 minutes in total. You can enter several legs, and the tool adds up the distance and ascent.
What the rule leaves out
The article says the rule assumes reasonable fitness, typical terrain and normal conditions, and that it excludes rest breaks. It lists later adjustments. Tranter's corrections allow for fitness and fatigue. Aitken's corrections (1977) use 2.5 miles an hour on rough ground, against 3 on paths. Langmuir (1984) adjusts for descent, subtracting time on gentle slopes and adding it on steep ones.
This tool uses the base rule only. It adds time for ascent and none for descent, rough ground or a heavy pack, so treat the result as a starting point and set your own turn-around time.
FAQ
Does a bigger scale number show more or less ground?
More ground. A 1:100,000 map covers more area per sheet than a 1:25,000 one, but each centimetre has less detail. The 1:25,000 map is the larger scale.
Does the tool allow for downhill sections?
No. It follows the base rule, which only adds time for ascent. Wikipedia notes that Langmuir's correction (1984) handles descent, adding time for steep descents.
Is Naismith's rule right for slower groups?
It assumes reasonable fitness, and Wikipedia says group hiking normally uses the slowest member's pace. If you are slower than the rule's pace, expect longer than the estimate.