You will use about half as much (by weight) of resin as you will fibreglass chopped-strand matting.

As a guide, for every square metre you will need about 280 grams for each millimetre thickness.

As an example, if you are producing a tool of area 0.75 sq m area, to a thickness of 3mm you will need 280 x 0.75 x 3 = 630 grams.