How Long Will a Hike Take? Naismith's Rule Worked Through
The quickest honest answer to "how long will this hike take?" comes from a rule written down in 1892 by a Scottish mountaineer, William Naismith: allow one hour for every 5 kilometres of distance, and add one hour for every 600 metres of climbing. It is still the planning figure behind a great many guidebook times, and it is the main estimate the Hiking Time Calculator gives you.
This guide works the rule through on four routes, shows what the calculator's pace setting changes, and is plain about what the number does not include. All the routes are hypothetical: put in the distance and climb of your own route from a map or a trail description.
The rule in one line
Naismith's rule treats a hike as two separate jobs. Moving across the ground costs time in proportion to distance: 5 km per hour, or 12 minutes per kilometre. Lifting yourself uphill costs extra time in proportion to the height gained: 600 m per hour, or 10 minutes for every 100 m of climb. Add the two and you have the estimate.
Two inputs matter, and both are for the whole outing, not one way:
- Distance is the total you will walk. For an out-and-back trail, that is double the one-way figure. For a loop, it is the loop length.
- Ascent is the total height you gain over the whole route, added up across every climb. It is not the summit height and not the difference between the trailhead and the top if the trail goes up and down on the way. A route that climbs 500 m, drops 100 m into a saddle and climbs 400 m more has 900 m of ascent.
The rule adds nothing for going downhill. That is a deliberate simplification, and it is the first thing to keep in mind when you read the result.
Worked example: 12 km with 800 m of climb
Take a hypothetical out-and-back route of 12 km in total, climbing 800 m to a high point and returning the same way. These are the calculator's default inputs, so you can check them yourself.
- Distance: 12 km at 5 km per hour = 2.4 hours.
- Climb: 800 m at 600 m per hour = 1.33 hours.
- Naismith estimate: 3h 44m of moving time.
The calculator also shows a second figure, the Tobler cross-check, which for this route comes out at 3h 01m. Tobler's hiking function works out walking speed from the steepness of the ground rather than adding a fixed allowance for climb. The two methods disagree by about three quarters of an hour here, and that gap is normal. The calculator recommends the Naismith figure because it is the more conservative of the two on most hill routes, and a conservative estimate is the safer one to plan around. Our guide to why Naismith and Tobler differ goes into the gap in detail.
What the pace setting does
Naismith wrote his rule for a fit walker carrying a day pack on reasonable ground. Not everyone moves at that speed, so the calculator scales the whole estimate by a pace factor:
- Brisk / fit multiplies the estimate by 0.85, which is 15% quicker.
- Average uses the rule as written.
- Leisurely / heavy pack multiplies by 1.25, which is 25% slower.
On the same 12 km and 800 m route, that gives:
| Pace | Distance portion | Climbing portion | Naismith estimate | Tobler cross-check |
|---|---|---|---|---|
| Brisk | 2.04 h | 1.13 h | 3h 10m | 2h 34m |
| Average | 2.4 h | 1.33 h | 3h 44m | 3h 01m |
| Leisurely | 3 h | 1.67 h | 4h 40m | 3h 46m |
The spread between brisk and leisurely on this one route is an hour and a half. That is why it is worth being honest about which setting describes you on the day: with a full overnight pack, with children, at the end of a long week, or on your first hill walk in months, "leisurely" is usually the right choice even if you are normally quicker. If you have a watch or app history from earlier hikes, compare your real times against the calculator's three settings and use the one that matches.
Three more routes
Here is the average-pace estimate on three other hypothetical routes, so you can see how the two parts of the rule trade off.
- 8 km with 300 m of climb. 1.6 hours for the distance plus 0.5 hours for the climb: 2h 06m by Naismith, 1h 49m by Tobler. A typical half-day hike.
- 16 km with 1,200 m of climb. 3.2 hours plus 2 hours: 5h 12m by Naismith, 4h 08m by Tobler. A full mountain day, before any stops.
- 10 km on the flat. Two hours exactly by Naismith, 2h 00m, and 1h 59m by Tobler. With no climb, the two methods agree almost to the minute, because both assume roughly 5 km per hour on level ground.
Notice how much the climb adds on the bigger route. On the 16 km day, the 1,200 m of ascent accounts for two of the five hours. Two routes with the same distance can differ by hours if one of them climbs and the other does not, which is why a distance-only estimate ("I walk at 4 km per hour") goes wrong in hill country.
What the estimate leaves out
The figure the calculator gives is moving time for a fit adult on a reasonable, well-marked trail in good conditions. It is an estimate, not a promise. A real day almost always takes longer, for reasons the rule cannot see:
- Breaks. Food, water, photographs, map checks, a stop at the top. Ten minutes every hour is a common allowance, and lunch at a viewpoint can easily take half an hour. Add them to the estimate yourself.
- Descents. Naismith adds nothing for going down. On gentle slopes that is fair, but steep, loose or rocky descents are slow and hard on the knees, and many walkers come down a steep path no faster than they went up it. Our turnaround time guide explains why the return leg usually needs more time than the outward one.
- Terrain. Scree, boulders, snow, mud, deep sand, river crossings, scrambling and overgrown paths can halve your speed. The rule assumes a path you can walk on without using your hands.
- Altitude. Above roughly 2,500 to 3,000 m, most people slow down noticeably, and the rule makes no allowance for thinner air.
- Weather and daylight. Heat, wind, rain, fog and darkness all slow you down. Navigation in poor visibility takes longer than walking a path you can see.
- Group size. A group moves at the pace of its slowest member, with more stops. See planning a group hike for the slowest walker.
A practical way to use the number: take the calculator's estimate for the right pace setting, add your breaks, then add a margin for anything the route description warns you about. That total is what you plan the day around.
From hiking time to a plan
The hiking time on its own does not tell you when to leave or when to give up on the summit. Two more steps turn it into a safe plan.
First, put the total into the Daylight Turnaround Calculator with your start time and the sunset time for the date. It gives you the latest time you should turn back, wherever you are on the route, to finish with a margin of daylight. A turnaround time is a hard rule: when it arrives, you turn around, even if the top is in sight.
Second, use the same hours to estimate water. The Water Needs Calculator takes the time on trail, the temperature and how hard you are working, and gives a planning figure for how much to carry.
Whatever the numbers say, carry the basics every time: a map and a way to navigate, extra layers, food and water, a first-aid kit, a headlamp, and a charged phone. Tell someone where you are going and when you expect to be back, and know the local emergency number for the area. Before any hike on a real trail, check the land manager's current conditions and any closures, because the calculator knows nothing about the state of the path today.
Common mistakes with the rule
- Using one-way figures. If the trail description gives 6 km to the summit, an out-and-back is 12 km. Entering 6 km halves the answer.
- Using summit height instead of ascent. A summit at 1,400 m with the trailhead at 900 m is 500 m of climb at most, more if the path dips on the way.
- Ignoring the climbs on the way back. On a route that drops into a valley before the final climb, the return includes a climb out of that valley. Count it.
- Treating moving time as total time. The estimate does not include a single stop.
- Choosing "brisk" because you are fit on a gym treadmill. Trail fitness, load and footing are different. Start with "average" and adjust from your own logged hikes.
Naismith's rule has lasted well over a century because it is simple and usually close enough to plan with. Treat it as the starting point, add what it leaves out, and let the clock, not the summit, decide when you turn around.