Naismith’s Rule

It’s always great to get feedback from friends that you have taught map reading and basic navigation.  However, recently a couple have been saying that they are now taking on more adventurous trips but their planned timings fall short of their actual timings.  When I taught them navigation we covered basic pacing and time keeping for flat ground, we had not covered climbing and descending – it was time to teach them about Naismith’s Rule!

So Who was Naismith?

WilliamNaismith
William Wilson Naismith (1856 – 27 September 1935) was a Scottish mountaineer and a founding member of the Scottish Mountaineering Club.

In 1892, he worked out a way of estimating the length of time it would take to cover a walking route, including ascents and descents

 

What is Naismith’s Rule?

In its most basic form his simple rule was to

“allow 1 hour for every 3 miles forward, plus ½ hour for every 1000 feet of ascent”.  

Note that Naismith made no allowance for descending.

These days we are more likely to use metric measurements, so this equates to approximately 1 hour for every 5 km forward, plus 30 minutes for every 300 metres of ascent, for an average walker.

Naismith's_rule.svg

The key points to take from this are the words approximately and average – because this rule is totally adaptable to an individuals personal requirements.  But more on that later.

As mentioned earlier, Naismith made no allowance for the decent thereby assuming that the time taken to descend was the same as the time to cover the horizontal distance.  This is, of course, totally untrue for several reasons:

  • A steep downhill section will in fact take longer than a flat section
  • A shallow slope will take the same or less for the same horizontal distance

To overcome this I use a multiplication factor to adjust descent times – I multiple the horizontal distance by 1.5, so a 20 min horizontal descent will take closer to 30 minutes to complete.  This is best experimented with to ascertain your particular descent rate over different terrains.

This leads me back to the words approximately and average.

The reality of Naismith’s Rule is that it is dependant on:

  • Fitness levels
  • Speed of the slowest person
  • Size of the group – larger groups tend to travel more slowly
  • The terrain – rocky, heather, boggy, deep undergrowth etc can all slow you down
  • Steepness of the slope?
  • Wind speed and direction
  • Weight being carried
  • plus many many more factors
drawingafineline
image courtesy of drawingafineline

As a result over the years it has been adapted and refined

A better approach is to start with 4 km per hour walking speed and 1 hour for every 600 m of climb.  If you adopt these timings then 4 km per hour, that would equal 1 km every 15 mins or 100 metres in 1½ mins.  600 m per hour, that would equate to 200 metres every 20 mins or 10 metres in 1 min.  For a slower walker then set a 3km pace, or 1km every 20 mins and 100m in 2 minutes.

Example:

In the example shown below I am heading up Pen-y-Fan at a rate of 4km/hr and 600m/hr.  The route is 3.14km long and the total climb (ascent) is 494m.

map.jpg

© Ordnance Survey

Horizontal time  =  dist ÷ rate × 60mins = 3.14 / 4 x 60 = 47 minutes

Vertical time  =  height ÷ rate × 60mins = 494 / 600 x 60 = 49 minutes

Total time  =  47 + 49 = 96 minutes or 1hr 36mins

When planning the timings for a full walk do not forget to factor in:

  • Food and rest breaks
  • stops for putting on/taking off waterproofs
  • Toilet breaks,
  • navigation,
  • Photography, note taking

Naismith’s Rule is, at best, a minimum time calculator, it is the start point.  Always be prepared to factor in extra time due to adverse weather, fatigue, unexpected terrain, visibility and navigation.

Every walker will have a different set of parameters for their personal walking speed and it is incumbant on all party leaders to keep this firmly in the front of their mind.  When walking with a large group, place an experienced walker at the back to keep pace with the slowest member of the party and call the pace for the rest of the party.  No one wants to see the main group pulling ahead, leaving the slower ones to struggle.

For further information I always refer back to my trusty tome – Mountaincraft and Leadership by Eric Langmuir.

n.b.  If you use one of the preparatory route planning softwares such as OS Maps, your personal walking speed can be set in the preferences.  However, be warned – you cannot adjust the climb/descent time algorithm so will need to take this into consideration.

Map extract supplied by Ordnance Survey

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