Answer: taking into account the route that the cable will have to take and providing an additional ten meters.
You are probably not going to directly connect the outbuilding to the switchboard by passing the electric cable in the middle of the garden? No, instead, you will run the cable along the walls, along the baseboards, maybe even bury part of the cable underground. To calculate the length of the cable required, all of these elements must be taken into account. So think carefully about the different places where the cable will pass, then measure with a meter the distance it really represents. You will have your answer. Add a few tens of centimeters more, even if you have to cut the cable afterwards, it is always good to have surplus in this kind of situation. But beware, the width of the cable also matters, it can vary depending on the power you need. Our practical DIY videos