How much material do I need for a tailor-made suit?

Double-breasted mod suit

Double-breasted mod suit

If you want a suit, asking for a ‘suit length’ at a cloth place should do the trick. But if they want specifics, around 3.5 metres should be good for a suit, 4 metres if you want a waistcoat too.

For just trousers, get around 1.5 metres, with 2 metres good for just a jacket. Most rolls of cloth are a standard width (150cm), so you shouldn’t have to worry about that. But you can always check, just in case it is vintage cloth with a smaller width (and thus, would mean you need a little more).