The distance of each walk is given at the head of each walking guide in miles and km. But in practice, this is not as simple as it sounds!
The figure you see has been read off from the length of the track as seen on Google Earth. The walk is recorded at first as a GPS track on a measuring device (Garmin or iPhone). It is then re-drawn, eliminating any mistakes, dead ends or irrelevant parts. The figure is then rounded up to the next mile or half mile (km or half km). This is what goes on page 1 of the guide.
If you measure the distance you walk, you may that your own reading is higher than the distance in the guide. There are several reasons for this:
1. The GPS is made up of straight bits - not arcs or rounded sections. It doesn't take account of swerving round gates, skirting round a hillside, following a curving path. It's like a "jerky robot".
2. The GPS does not use Pythagoras! If the gradient is significant, the actual distance travelled is more than the vertical projection (looking down from the heavens). Especially since, when the legs and knees are not so tolerant of gradients, we tend to weave our way up a steep hill.
3. Every walker adds to the length by walking "off piste" to sit, look at a view, make a small correction, skip holes and puddles, parking the car a little further away, etc. etc.