Naismith’s rule, named after William W. Naismith, was devised in 1892 to estimate the time taken to cover distances in the mountains.
He estimated that you:
allow 1 hour per 5km walked and 1 hour for every 600m ascended.
If you ever do a Mountain Leader or Navigation course, then you’ll have this drummed into your head. Usually down to 12 minutes per km and 10 minutes per 100m ascended, or even down to the level of working out that 100m takes you 1 minutes and 12 seconds, and multiplying upwards from that for micro navigation in order to estimate distance along with pacing. A pacing card is below, or download it in Excel -Pacing_Timing_Card_Creator.
So, you’ve got a walk that’s 10km and 1200m ascent. The 10 km takes you 2 hours (1 hour per 5km) and the 1200m another 2 hours (600m per hour) so the entire walk should see you walking for 4 hours. If that seems quick, then it certainly is!
What Naismith doesn’t allow for. Naismith didn’t believe in stopping for breaks, admiring the view or general dilly dallying along the way. Well, he might have done for all I know, but he didn’t allow for this in his rule. So you need to add that as well and how long is a piece of string.
You may think that’s the end of it. But no. For example, Snowdon should take about 4 hours according to Naismith – which is similar to the example given above. However, I can complete it in a lather in well under three hours. But, factor snow into the equation and the same walk has taken me over 6. Not to mention the fact I also had a hangover that day. I think you start getting the idea.
Another factor that you need to factor in is the underlying terrain. The Snowdon Ranger is a very easy path in mountaineering terms and so it’s straightforward enough to complete it comfortably in the Naismith time. However, scramble up Crib Goch and you can almost double the ascent time. Walks in areas such as the Rhinogydd can easily take twice the time estimated, especially along the badlands area (Llyn Pryfed). One rule of thumb is to modify your hourly pace to 4kmh instead of 5, though for some sections you expect to be tough going you can reduce this to 3 or even 2kmh over terrain that’s particularly heavy going (bogs and scrambling perhaps).
The weather can hamper you further. Strong winds and heavy rain slows you down and dampens the spirit. Wet rock underfoot also slows you down, and I find that while I usually gain time on a dry descent, it’s much more difficult to do so in the wet. Just to complicate it further, if the weather is particularly foul then you will stop for less breaks and they’ll be shorter, so you can end up gaining time that way as well!
Complicating it even further, if you’ve got an inexperienced party member then you’ll have to slow your times down to match theirs. You may know your speed down to the minute, but taking novices on the hill brings in a whole new level of uncertainty. Make sure you give yourself plenty of slack, and assign a point of no return, at which you know that if you’re not at the top you’ll just have to turn back.
Carrying an overnight pack will modify it, though if you’re travelling particularly lightweight you shouldn’t find it weighs you down considerably. Even with 5 days’ supplies in Knoydart, we averaged 4 hours for every 5 estimated by Naismith, including the time taken to cook and eat a leisurely lunch and soak in the scenery.
Finally, there are alternative modifiers that you can use for descent. Sometimes going downhill, where the gradient is easy you can gain time – so you can subtract 10 minutes per 300m or alternatively if it’s particularly steep then you can add an extra 10 minutes per 300m of descent.
You may choose to bypass all this and take the guidebook time as gospel. They’re usually the opinion of the author combined with Naismith. This also goes for the routes on this site. Some books offer paces that are rather frightening – Irvine Butterfield’s High Mountains book being one particular example.
So – what’s the bottom line? Our 4 hour walk above can take anything from 2.5 hours to 6 or 7 depending on the conditions, how hard you want to push yourself, where you’re walking and of course the speed of the slowest member of the party. In my walking log I can see that the estimated Naismith time for walks on Snowdon are within 97% of the actual time, and that’s over hundreds of trips, so proved itself quite accurate. However, my Rhinogydd trips are completed much slower with the Naismith time being only 69% of the total. It might make more sense to calculate them the other way around, but I’m used to trying to get my walks in at over 100%.
So as I’ve compared my actual times to the Naismith times, it gives me a decent idea how long I’ll take on different types of trips. If you don’t want to go to that extreme then add 25% if you expect conditions to be foul, or even 50% if you think they’re exceptional. All of the modifiers given above are just rules of thumb, and the entire rule is one to be used with care. Other suggestions include adding a % for snow and other conditions, but it can end up rather complicated.
You can also cheat! Plot your route in route-plotting software such as Tracklogs, and it automatically calculates the standard Naismith rate. You can modify this to suit, perhaps changing the pace to 4kmh, and also by adding modifiers for descent. It doesn’t take into consideration the nature of the terrain, only the distance along with the ascent and descent undertaken in that distance. However, it does give you the basic estimate, which you can then modify to your heart’s content. Download our free Excel timing calculator with some sample modifiers – here or just look at the image at the top of the page.
However, if you take the points above into consideration then you should be able to better estimate your timings and ETA on each walk. If you’ve got a deadline such as darkness falling or missing the last train, then it’s a skill you soon develop out of necessity!