I was recommend 'Mentor smooth round high profile - gel breast implant cohesive I' 425 cc - how much does each implant weigh?

For most purposes cc's (a measure of volume) and grams (a measure of weight) are commonly considered equivalent. If you wanted to be more precise, then one cc weights slightly more than one gram. The exact conversion between the two units would depend on the density of the specific gel used, so it is impossible to give you an exact value. Very roughly, you can expect a 425cc silicone implant to have a weight around 435-440g.