There are three different routes up Mont Ventoux - here's an overview plus a downloadable GPX file with them all.
This is the 'classic' Tour de France climb. It's 21.5km long and sees you gain around 1610 metres. It's a brutal, relentless climb – from around Sainte Estève to Chalet Reynard, you'll ride at a gradient of around 9-10%. By far the most popular of the three routes.
A quieter route but no less challenging. Its stats are similar to the classic climb (21km with an ascent of 1570 metres), but its gradients are more variable.
A longer climb but a more forgiving gradient, the Sault side is generally seen as the 'easy' options and it offers a more gentle experience than the other two routes. It's 26km with 1220 metres gained.
Download GPX file (Thanks to Will for allowing me to share his GPX files)