I'm really new to French, as I've been living in France for a couple of weeks only. So I want to get a haircut that in many countries is called a #1 haircut, which is essentially the next-shortest after 0, but I've no idea how to do it. Any suggestions?
I would ask for:
Une coupe à la tondeuse, sabot de 3 mm (ou 2,5 mm)
Even though the question is about France, I want to add some information for the Quebec province. Here in Quebec, we use the exact same system for clippers. So you could just ask something along:
Je voudrais me faire raser au [numéro] 1