What scale are OS maps?

Ordnance Survey Explorer maps are 1:25,000 (4cm = 1km). OS Landranger maps are 1:50,000 (2cm = 1km). Harvey maps come in 1:25,000 and 1:40,000 scales. For mountain navigation, 1:25,000 is preferred.

How does terrain affect actual distance?

Map distance is the flat (horizontal) distance. Walking over hills means you cover more ground than shown on the map. Undulating terrain adds about 5%, hilly terrain 10%, and mountainous terrain 15% to the flat distance.

What is Naismith rule?

Naismith estimated that a fit walker covers 5 km per hour on flat ground, plus an additional 1 minute for every 10 metres of ascent. This gives a realistic time estimate for hill walks.

How accurate is the time estimate?

Naismith is a good baseline for fit walkers. For groups, add 20-30% extra time. For poor weather or heavy packs, add 10-20%. Tranter corrections can adjust for fitness level but add complexity.

Should I use flat or adjusted distance for planning?

Use adjusted distance for a more realistic expectation of how far you will actually walk. Use flat distance for comparing with map measurements and grid references.

CampCalcs

Map Distance Calculator — Actual Hiking Distance from Map

Measure actual hiking distance from map with terrain adjustment and Naismith time estimate.

Map Distance

Measured on the map

Map Scale

Enter the map scale

Terrain

Type of terrain or ground

Use Naismith's Rule

Estimate walking time including ascent penalty

How We Calculate This

Map to Real Distance

Real Distance = Map Distance (cm) x Scale

On a 1:25,000 map, 1 cm = 250 m. On a 1:50,000 map, 1 cm = 500 m.

Terrain Adjustment

Terrain factors add 0-15% to flat distance to account for the actual ground covered over hills and rough ground.

Naismith Time

Base pace of 5 km/hr plus 1 minute per 10 m of ascent. Estimated ascent is derived from terrain type.

Frequently Asked Questions

Related Calculators

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Convert between 6-figure and 8-figure OS grid references with easting and northing.

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Calculate the bearing between two grid references or coordinates.

Pace Counter Calculator

Calibrate your pace count for accurate distance measurement on foot.

Walking Time Calculator

Estimate walking time using Naismith's rule with Tranter's corrections for fitness.

Elevation Gain Calculator

Calculate total elevation gain and loss from a series of height points along a route.

Last updated: February 2026

All calculations are estimates. Always verify conditions and use proper safety equipment outdoors.