Naismith's Rule: how to estimate hiking time

Most people who finish a hike by headlamp were never lost. They just thought the walk was shorter than it turned out to be.

Naismith's Rule is the oldest fix for that. Allow one hour for every 5 km (3 miles) of distance, plus one hour for every 600 m (2,000 ft) you climb. It turns a line on a map into a time estimate in about ten seconds. The catch: that number is a floor for a fit walker, not a promise for your actual day.

Key takeaways

• The formula: 1 hour per 5 km + 1 hour per 600 m of ascent (metric); 1 hour per 3 miles + 1 hour per 2,000 ft (imperial).
• Shortcut: about 12 minutes per kilometre, plus 10 minutes for every 100 m you climb.
• It is a minimum. Naismith ignores breaks, descent, fitness, pack weight, terrain, altitude, and weather.
• Read it as the fastest you could plausibly go, then set your turnaround by a slower pace.

What Naismith's rule is

Naismith's Rule estimates walking time from two numbers you can read straight off a map: how far you are going, and how much height you gain. William W. Naismith, a Scottish mountaineer and a founder of the Scottish Mountaineering Club, published it in 1892 as "one hour per three miles on the map and an additional hour per 2000 feet of ascent" (Naismith, W.W., SMCJ 2(3):136, 1892; documented at Naismith's rule). A century on, it still sits under almost every hiking-time calculator, because it needs no special data and, used honestly, keeps you on the right side of dark.

On the trail the metric version is easiest to run as a total: about 12 minutes per kilometre, plus 10 minutes for every 100 m you climb. Classic Naismith counts distance and ascent only. Descent is treated as free, which is the rule's biggest blind spot, and we fix it below.

A worked example

Say your route is 12 km with 800 m of ascent.

• Distance: 12 km at 12 minutes each is 144 minutes.
• Ascent: 800 m is eight lots of 100 m, so 80 minutes.
• Total: about 224 minutes, or 3 hours 44 minutes.

That 3 hours 44 is a fit walker moving without stopping. It does not include lunch, photos, a careful descent on tired legs, or the drag of a heavy pack over rough ground. On a real day the same route can take five hours or more.

Why the answer is always a little optimistic

This is the part most calculators skip, and the part that keeps you safe. Naismith describes one specific walker: fit, steady, unloaded, in good conditions, not stopping. Your day usually differs on at least one count, and every difference adds time.

• Breaks. Lunch, water, layers, and navigation add up faster than you expect.
• Descent. A long or steep downhill is slower than flat ground, not free.
• Fitness and fatigue. Your pace late in a long day is not your pace at the car.
• Pack weight. A heavy load slows you, most of all on the climbs.
• Terrain. Bog, scree, snow, and pathless ground can halve your speed.
• Altitude and weather. Thin air, heat, wind, and poor visibility all cost time.

In a group, pace the rule to the slowest person so nobody gets left behind. Treat the Naismith number as the fastest you could plausibly finish, then plan the day, and your latest safe turnaround time, around something slower.

The corrections experienced hikers add

Three refinements sit on top of Naismith, and they turn a rough guess into a plan.

Speed changes with the slope (Tobler). Naismith treats every kilometre the same; in practice your pace depends on the gradient. Tobler's hiking function captures it: about 5 km/h on the flat, a little over 6 km/h on a gentle downhill, and a steep fall-off as the ground tilts either way, with off-path travel around 60% of on-path speed (Tobler, W., NCGIA Technical Report 93-1, 1993; see Tobler's hiking function). Most modern GPX calculators use a Tobler-style curve rather than flat Naismith.

Descent is not free (Langmuir). Eric Langmuir's correction, long standard in British mountain training, patches Naismith's blind spot (Langmuir, E., Mountaincraft and Leadership, 4th ed., 2013): for a gentle downhill of about 5 to 12 degrees, subtract 10 minutes for every 300 m of descent; for a steep one over about 12 degrees, add 10 minutes for every 300 m. That second line catches people out, because a steep, knee-jarring descent is slower than the flat, and it usually comes at the end of the day when the light is going.

Adjust for your own fitness (Tranter). Tranter's corrections scale the Naismith time up or down by how fast you climb a set test hill, and add time for fatigue over a long day (documented alongside Naismith's rule at Naismith's rule). You do not need the table to use the idea: be honest about your fitness, and add time as the hours pile up. For roped alpine ground and glacier travel, most people switch to the Munter method, built for that terrain.

Where Naismith fits, and where it doesn't

Naismith answers one question, how long, and answers it well. But time is only one part of how hard a route is. A short, gentle walk can still be serious if it is exposed, unmarked, or crosses a glacier, and Naismith sees none of that.

That is why we grade routes on five separate axes instead of one label: physical, technical, exposure, environment, and navigation. Naismith feeds the physical one and cannot see the other four. For the full picture, see how we rate trail difficulty honestly.

Frequently asked questions

Is Naismith's rule accurate?

It is accurate for what it claims: the least time a fit walker needs, based on distance and ascent, in good conditions. For a normal day it reads low, because it leaves out breaks, descent, fitness, pack, and terrain. Use it as a floor and add your own margin.

What is the Naismith's rule formula?

Allow 1 hour for every 5 km (3 miles), plus 1 hour for every 600 m (2,000 ft) of ascent. As a shortcut, that is about 12 minutes per kilometre plus 10 minutes for every 100 m you climb.

Does Naismith's rule account for descent?

No. Classic Naismith counts distance and ascent only, and treats descent as free. Langmuir's correction fixes it: take time off for gentle descents, but add time for steep ones, which are slower than the flat.

How much time should I add to a Naismith estimate?

There is no single figure, because it depends on your fitness, pack, the ground, and how often you stop. A common starting point is to treat Naismith as the minimum and plan for a third to a half more, then adjust once you have compared it against your real times.

The short version

Naismith's Rule lasts because it is simple and it works, as a minimum. Learn the shortcut (12 minutes per kilometre plus 10 minutes for every 100 m of ascent), remember that it ignores everything that slows a real day down, and always set your turnaround by a pace slower than the rule suggests.

Then put in your route and get an honest, personal time from the "Can I do this hike?" planner.