I generally assume that (for wider fabrics around 58 to 60 inches) I will be able to get a top with sleeves or skirt from 2 metres, and a dress from 3 metres. Trousers are another matter entirely, but 2 metres may well be OK, 3 metres will be. If I have something in mind that's different to the things I usually make I usually buy a bit extra, just to be sure.
44/45 inch fabrics I don't usually buy less than 3 metres, and I'd want to check a pattern if it was for trousers.
If it's a remnant and I love it, I'll figure something out later.