Naismith's Rule Calculator

Naismith's Rule was published in 1892 by William W. Naismith, a Scottish mountaineer and one of the founders of the Scottish Mountaineering Club. It's the foundational walking-time formula for UK hillwalking and has barely changed since.

The base formula is straightforward: allow 1 hour per 5km of distance, plus 1 hour per 600m of ascent. A 10km walk with 400m of ascent comes out at 2 hours 40 minutes by Naismith's original reckoning. In practice this is only a starting point — it assumes a fit walker on good ground in good weather with a light pack.

Tranter's corrections (1972) extended Naismith to account for fitness level and carry weight. We simplify Tranter's full lookup table into five fitness tiers, because form-based lookups are tedious and the simplification sits well within the ±25% real-world variance.

Scottish-specific adjustments come on top: peat bog and scree/boulder fields get their own terrain multipliers (most generic calculators ignore these), strong wind and whiteout get weather multipliers, and pack weight is tiered for day / multi-day / expedition kit. The result is a more realistic time estimate for Scottish hill conditions than you'd get from a generic Naismith tool.

Langmuir's descent correction (1984) is also applied when you enter a descent figure: subtract 1 minute per 10m of descent on slopes above 5°. This saves time on linear routes that end lower than they begin — a ridge traverse or a point-to-point finish in a glen. The saving is capped to the ascent component so the base time can never drop below the flat-ground minimum.