I learned the same thing, in primary school. The old measure toise is really from fingertip to fingertip. If you can walk trough with arms outstretched, it's far enough apart. Another one you'll also find frequently is 135 cm, or from shoulder tip to opposite fingertip. It's the standard measurement for lengths of cloth. Those old measurements are a fascinating subject, an old schoolteacher of mine used them to teach us about Medieval history, always pointing out that Brabantian measures were bigger than Flemish or French :-)
Bonne fêtes, j'espère qu'il y aura de beaux livres sous ton sapin.