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OutdoorSCOT

Technique

Naismith's Rule

Definition

Naismith's Rule is a formula for estimating walking time in hilly terrain: allow one hour for every 5 km of distance, plus an additional hour for every 600m of ascent. For most fit walkers carrying day kit on good paths, this gives a usable baseline figure. Various corrections exist for fatigue, descent, snow and pack weight.

Etymology & origin

Devised in 1892 by William Wilson Naismith, a Glasgow-born mountaineer who was a founder member of the Scottish Mountaineering Club. Naismith published the rule in the SMC Journal as a back-of-the-envelope calculation for trip planning. The original article suggested the formula was 'a guide rather than a prescription' — a caveat that has been routinely ignored in the 130 years since.

Context & usage

Naismith's Rule is the universal baseline for Scottish hill day planning. Mountain rescue teams, guide companies, walking clubs and individual walkers all use the same formula. The standard outputs:

- 5 km on flat = 1 hour - 5 km with 600m ascent = 2 hours - 10 km with 1,000m ascent = 3 hours 40 minutes

The rule's weakness is the same as its strength: it's a generic formula that ignores everything specific about you, the conditions, and the terrain. Walkers under-fit, over-loaded, walking in bog, walking in snow, walking in heat or descending on knees all need corrections. The most common corrections:

- **Tranter's correction**: adjusts for fitness level (walkers at different fitness grades take different multiples of the Naismith time) - **Munter's adjustment** (Alpine origin): factor pack weight more heavily - **Aitkin's correction**: account for ground roughness and conditions

For Scottish hill days, Naismith + 20% is a reasonable starting point for walkers carrying day kit on average paths. Add 50% for trackless ground, peat bog, or winter conditions. The OutdoorSCOT Naismith Calculator at /tools/naismith adjusts for difficulty grade automatically.

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Reviewed 2026-05-28

All glossary entries

Naismith's Rule — common questions

Does Naismith account for descent?
The original rule does not — descents are treated as adding zero time. This is genuinely wrong for steep descents (knees slow the pace) and slightly conservative for gentle ones. Tranter's correction and other extensions add descent time; the OutdoorSCOT calculator adjusts for steepness.
Why is Naismith's Rule still used after 130 years?
Because it's simple enough to do in your head and accurate enough for trip planning at the broad-brush level. The corrections that improve accuracy add complexity that walkers rarely use. For 'will this walk take 5 hours or 8?' Naismith is reliable; for 'will I arrive at 4pm or 4:23pm?' use a more detailed model.