Short answer
Naismith’s rule allows one hour for every 5 km of horizontal distance, plus one hour for every 600 m of ascent. For a 14 km route with 900 m of climb, that gives 2.8 h plus 1.5 h, or 4 h 18 min of moving time. It leaves out rests, descents unless corrected, navigation and load, so calibrate it on routes you know.
Naismith’s rule estimates moving time for a walk from two inputs: horizontal distance and total ascent. Allow one hour for every 5 km on the map, plus one hour for every 600 m of climb. In metric form that is a base pace of 5 km/h plus 10 minutes for every 100 m of ascent. It gives moving time only, so rests and load have to be added separately.
Where the rule comes from
William W. Naismith, a Scottish mountaineer, devised the rule in 1892 while walking Cruach Ardrain, and he recorded it in a note in the Scottish Mountaineering Club Journal. The original is in miles and feet: one hour for every 3 miles, plus one hour for every 2,000 ft of ascent. Wikipedia’s article on the rule gives both forms, cites that note and describes the rule as a rule of thumb.
The metric arithmetic
Convert both parts to hours and add them:
moving time (h) = distance (km) ÷ 5 + ascent (m) ÷ 600
The distance term is the flat walk. The ascent term is the climb allowance. Ten minutes per 100 m is the same allowance written another way: 100 m ÷ 600 m per hour is one-sixth of an hour, which is 10 minutes.
Adding the descent corrections
The rule counts only ascent, so a long descent adds nothing. Langmuir’s corrections add a term for descent. Wikipedia summarises them from Eric Langmuir’s handbook Mountaincraft and Leadership. On a gentle descent of 5 to 12°, subtract 10 minutes for every 300 m of descent. On a steep descent over 12°, add 10 minutes for every 300 m. The bands do not cover slopes under 5°, so a long, nearly level descent needs a judgement of its own.
Tranter’s corrections go further and adjust for fitness and fatigue. Fitness is judged from the time taken to climb 1,000 ft (305 m) over half a mile (800 m). The Trail time tool does not include them. Its descent setting offers three choices: none, which follows the original rule; gentle; and steep.
Ascent as horizontal distance
The rule also fixes an exchange rate between climb and distance. Three miles per hour against 2,000 ft per hour gives 3 mi ÷ 2,000 ft = 7.92. One foot of climb therefore counts as 7.92 feet of flat walking. Wikipedia credits Philip Scarf with naming this Naismith’s number and rounding it to 8. The metric version gives 5,000 m ÷ 600 m = 8.33. The two rates differ by about 5%, because 8.33 ÷ 7.92 = 1.05.
The same exchange rate gives an equivalent flat distance. For the worked example below, 900 m × 8.33 ÷ 1,000 = 7.5 km of climb-equivalent distance. Added to 14 km, that is 21.5 km, and 21.5 km ÷ 5 km/h = 4.3 h, the same total as the two-part sum.
One route, four settings
The route is 14 km long, with 900 m of ascent and 900 m of descent. The base pace is the rule’s 5 km/h, and the first figure has no rests. Each later line changes one input.
Worked example: 14 km, 900 m up and 900 m down
The first line is the original rule. The second subtracts the gentle-descent correction from the moving time. The third adds 10 minutes of rest for each hour of moving time.
Original rule 14 ÷ 5 = 2.8 h; 900 ÷ 600 = 1.5 h; total 4.3 h = 4 h 18 min Gentle descent 900 ÷ 300 × 10 = 30 min less; 4 h 18 min − 30 min = 3 h 48 min Rests 3 h 48 min = 228 min; 228 × 10 ÷ 60 = 38 min Total 228 min + 38 min = 266 min = 4 h 26 min
Run the original rule in Trail time, or run the gentle-descent version with rests in the same tool.
The four settings of the same route are summarised below. The 43 minutes of rest in the first row is 258 minutes of moving time × 10 ÷ 60.
| Setting | Moving time | Rests added | Total time |
|---|---|---|---|
| Original rule, descent ignored | 4 h 18 min | None | 4 h 18 min |
| Original rule, 10 min rest per hour | 4 h 18 min | 43 min | 5 h 01 min |
| Gentle-descent correction | 3 h 48 min | None | 3 h 48 min |
| Gentle-descent correction, 10 min rest per hour | 3 h 48 min | 38 min | 4 h 26 min |
Calibrate the numbers on a route you know
The 5 km/h base is the rule’s assumption, not a measurement of you. The Trail time tool has two inputs for your own figures: pace, the flat walking speed in km/h, and climb, the minutes added per 100 m of ascent, which defaults to 10. To set them, time a route you know, remove the climb allowance from its moving time, and solve for pace.
climb allowance (min) = ascent (m) × climb ÷ 100 flat time (min) = moving time − climb allowance pace (km/h) = distance ÷ (flat time ÷ 60)
A hypothetical run of 6 km with 300 m of ascent and 95 minutes of moving time gives a climb allowance of 300 × 10 ÷ 100 = 30 min, a flat time of 95 − 30 = 65 min, and a pace of 6 ÷ (65 ÷ 60) = 5.5 km/h. Choose a calibration route with little descent, or set the descent rule to match its slopes, so that the descent does not distort the pace.
Where the rule underestimates
The rule has one flat pace and one climb rate. It has no term for the surface, so it treats a forest track and loose scree in the same way. The Trail time tool has no terrain, weather, fitness or group-size model either, so those effects must enter through the pace input. Lower the pace for rough ground, deep snow, long grass or bog, and for a heavy pack, then check the result against a route you have timed on similar ground.
The effect is largest on a rough section. A hypothetical 2 km boulder field walked at 2.5 km/h takes 2 ÷ 2.5 = 0.8 h, or 48 minutes. The same 2 km at the rule’s 5 km/h takes 24 minutes. The gap is 24 minutes on one section, and the rule would not show it.
Applying the rule leg by leg
A route total hides where the time goes. A 2 km leg with 400 m of climb takes 2 ÷ 5 × 60 = 24 min of flat walking and 400 × 10 ÷ 100 = 40 min of climb allowance, so the climb takes longer than the distance. Split the route at each change of slope, path or surface. Measure distance and ascent for each leg from the map, apply a descent correction only to legs that fall in a Langmuir band, and add the leg times.
The slope of each leg decides which descent band applies. Slope from contour lines shows how to read it from a map. On a leg with a steady grade, Tobler’s hiking function gives an alternative speed for that slope, and the two methods can be compared on the same leg.
Moving time gives a finish time only when the rests are added and the day is otherwise clear. Compare the finish with the time of sunset at the start, using the arithmetic in sunset and remaining daylight. A turnaround time sets a point after which the group turns back, and it should leave time for the walk out.
What the rule leaves out
The rule also leaves out weather, daylight, navigation errors, the pace of the slowest group member and the energy cost of a pack. The Pandolf equation guide covers how a load changes walking energy. The rule has no load term, so a heavier pack calls for a lower pace input, not a separate correction. Treat the result as one estimate in a plan, and revise it with each leg you time.
Common questions
Does Naismith’s rule work for scrambling?
Not as a time estimate. Wikipedia notes that the rule cannot be used for scrambling routes, and in the Yosemite Decimal System it applies only to Class 1 hiking. For steeper ground, use training and local guidance, and time the route on the day.
What does Langmuir’s correction change?
It adds or subtracts time for descent only. On a gentle descent of 5 to 12°, 10 minutes is subtracted for every 300 m descended. On a steep descent over 12°, 10 minutes is added for every 300 m.
Does the rule include rest breaks?
No. It gives moving time only. The Trail time tool adds breaks as minutes of rest per hour of moving time. On 4 h 18 min of moving time, 10 minutes per hour adds 43 min, for 5 h 01 min in total.
Sources
Published 2 November 2026. Reviewed 2 November 2026. Sources support the figures quoted; they do not endorse Trailwright. Report a correction through the owner’s contact page.