naismith rule

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 ascents. The rule was devised by William W. Naismith, a Scottish mountaineer, in 1892. The basic rule is as follows:

Allow 1 hour for every 3 miles (5 km) forward, plus ½ hour for every 1000 feet (300 metres) of ascent.
When walking in groups, calculate for the speed of the slowest person.

The basic rule assumes hikers of reasonable fitness, on typical terrain, under normal conditions. It does not account for delays, such as extended breaks for rest or sight-seeing, or for navigational obstacles. For planning expeditions or walks a party leader may use the rule in putting together a route card.

In practice, the results of Naismith's Rule are usually considered the minimum time necessary to complete a route. Over the years several "corrections" have been formulated in an attempt to make the rule more accurate. The most common correction is to add 25 or 50% to the time found with Naismith's Rule. While this may be more accurate for some people or under certain conditions, it does not explicitly account for any additional variables.

Other common corrections are:

When walking on poor terrain, allow 1 hour for every 2.5 miles (4 km) forward, instead of 1 hour per 3 miles.
On a gentle decline (about 5-12°), subtract 10 minutes per 1000 feet of descent. On a steep decline (over 12°), add 10 minutes per 1000 feet of descent.

Tranter's corrections
Tranter's corrections make adjustments for fitness and fatigue. Fitness is determined by the time it takes to climb 1000 feet over a distance of ½ mile (800 m). Additional adjustments for poor terrain or conditions can be estimated by dropping one or more fitness levels.

Individual fitness in minutes Time taken in hours estimated using Naismith's Rule
2 3 4 5 6 7 8 9 10 12 14 16 18 20 22 24
15 (very fit) 1 1.5 2 2.75 3.5 4.5 5.5 6.75 7.75 10 12.5 14.5 17 19.5 22 24
20 1.25 2.25 3.25 4.5 5.5 6.5 7.75 8.75 10 12.5 15 17.5 20 23
25 1.5 3 4.25 5.5 7 8.5 10 11.5 13.25 15 17.5
30 2 3.5 5 6.75 8.5 10.5 12.5 14.5
40 2.75 4.25 5.75 7.5 9.5 11.5 Too much to be attempted
50 (unfit) 3.25 4.75 6.5 8.5

For example, if Naismith's Rule estimates a journey time of 9 hours and your fitness level is 25, you should allow 11.5 hours