It is not possible to decide this in the abstract. It all depends on how far it is to the next village and what amenities are there. For us, a short day would be 15 km, a long day 35 km or more.
Most of our very long days have been forced upon us by wrong information about the non-existent facilities in the villages ahead. There is a double pain in this – not only does it mean more hours of walking, but those extra hours are in the hottest part of the day.
On our nineteen trips to France we have walked a total distance over 12,000 km in 531 walking days; around 23 km/day, walking for an average of five hours each day.
Our speed whilst walking is about 5.5 km/hour, but with our many stops for photography, drinks of water and consultation of the map, our average speed is around 4.5 km/hour.
We also walk a surprising distance without packs after arriving at our destination – exploring the village, visiting the local restaurant, even going to and from the sanitaires. On average this amounts to about three kilometres per day.