Quick Answer — What Naismith's Rule Says
Naismith's Rule was devised by Scottish mountaineer William W. Naismith in 1892 as a simple rule of thumb for estimating hiking time. In its original form: allow 1 hour for every 3 miles (5 km) of distance, plus 1 hour for every 2,000 ft (600 m) of elevation gain. Time = Distance/(3 mph) + \frac{Elevation Gain}{2{,}000 ft}.
It's a planning estimate for moving time only — it doesn't include breaks, photo stops, or lunch, and it assumes a hiker of reasonable fitness on typical, non-technical trail. Naismith's Rule applies to Class 1 hiking terrain (established trails) and was never intended to cover scrambling or technical routes.
Because the base rule ignores fitness, terrain roughness, and descent, two well-known refinements are commonly layered on top: Aitken's variant (1977), which slows the flat-ground pace on rough or off-track terrain, and Tranter's corrections, which adjust the estimate based on a hiker's actual fitness level and terrain roughness. This calculator supports all three.