How accurate are time estimates for French hiking paths?

Reader question: When I am hiking in France, I notice that the signs often show an estimated time left on the trail. How accurate is this, and how is it worked out?

Signage for walkers in France often contains an estimate of the amount of time it will take to reach a specific point or final destination.

A well-known way of calculating this, used in a number of countries, is the ‘Naismith rule’, a formula developed by Scottish mountaineer William Naismith in 1892.

It states that it takes an average hiker an hour to walk five kilometres without any breaks. 

For every 600 metres of increased elevation, an additional hour must be given (or half an hour for 300 metres, etc).

Walking time can therefore be worked out by using the formula: (distance in km ÷ 5) + increased elevation over the walk ÷ 600), thus a 10km walk involving 300m of going uphill would take 2+0.5 = 2.5 hours.

On French hiking and mountain footpaths, the signs are usually maintained by the Fédération française de randonnée pédestre (French hiking federation; FFR), which took this principle but modified it.

The FFR allows an hour for every four kilometres on flat terrain but uses different calculations for uphill and downhill sections, deeming that a walker can climb up 300m or descend 400m in one hour.

This is less simple to reduce to an easy formula, but generally allows a bit more leeway than Naismith, allowing for heavy backpacks, slower climbs and careful descents.

The times given represent an average, so you should adapt them depending on your fitness, the weather conditions, how much you are carrying etc.