It's important to calculate what you need in advance so that you have this information available to pass on to prospective suppliers. Being vague or 'not really knowing yet' can create hurdles further down the line.
Once again, it’s all in the details. Suppliers need to know the estimated order quantity, otherwise after arranging samples, providing prices and working out delivery details, they will then fall at the final hurdle: “I can’t order as much as 1000 metres. I only need around 150 metres.”
Be completely transparent about your needs and that way, suppliers can tell you up front if they are able to work with your quantities. It will save everybody a lot of time and work, including yourself. It’s worth mentioning at this point that most mills will have a MOQ (minimum order quantity), which can be anything from 40-3000 metres and above. If you don’t think you will need this sort of quantity, try to work with fabrics already in a supplier’s collection. You’ll need to be adaptable and learn to compromise.