Naismith’s rule is a rule of thumb that helps in the planning of a walking or hiking expedition by calculating how long it will take to walk the route, including the extra time taken when walking uphill. It was developed by William Naismith, a Scottish Mountaineer in 1892.
It can be expressed as : Allow 1 hour for every 3 miles (5 km) forward, plus 1 hour for every 2000 feet (600 metres) of ascent. The basic assumption made by Naismith was that hikers are of reasonable fitness, on typical terrain, under normal conditions. The rule also assumes that travel will be on trails, footpaths, or reasonably easy ground. It is possible to apply adjustments or “corrections” for more challenging terrain, although it cannot be used for scrambling routes.
Naismith’s rule takes no heed of the slowing influence of heavy loads, fatigue, rest stops, delays caused by tricky navigation – in poor visibility perhaps, adverse weather such as a strong headwind, or the ground underfoot.
Thus in practice, Naismith’s rule should be just used as a starting point for working and planning your timings. For planning expeditions a team leader can use Naismith’s rule in putting together a route card.
Alternatively, the rule can be used to determine the equivalent flat distance of a route. This is achieved by recognizing that Naismith’s rule implies an equivalence between distance and climb in time terms: 3 miles of distance is equivalent in time terms to 2000 feet of climb. This rule is usually used to consider the minimum time necessary to complete a route.
Over the years, several revisions to the rule have been made in order to account for some of the variables like load carried, roughness of terrain, descents and fitness (or lack of it). These corrections include:
1) Tranter’s corrections: It accounts for fitness and fatigue. He developed a fitness test to determine the time it takes to climb 1000 feet over a distance of 800m. Additional adjustments for uneven or unstable terrain or conditions can be estimated by dropping one or more fitness levels. The following chart can be used for calculating time required for the hike according to Tranter.
For both distances he gives an additional 1 h per 2000 ft (600 m) of ascent.
3) Langmuir’s corrections: Langmuir suggested the following corrections to Naismith;s model.
- Reduce the basic speed to 4km per hour
- On gentle descents between 5-12 degrees subtract 10mins per 300m of height loss (you’ll be trotting downhill fast)
- On steeper descents of 12 degrees and more add 10mins per 300m of height loss (you’ll be picking your way slowly)
Walking is an individualistic feature and is different for everyone. However, Naismith’s rule gives us a rough estimate of the relation between hiking distance and time required. At the end of the day, it depends on the individual’s comfort how long it takes him/her to complete the hike.