I'm not the one who makes jam in this house, DH is the one. However I know that he uses the same weight of fruit as he does for sugar, so 1kg of fruit = 1 kg of sugar. There's a bit of water in there but I have no idea how much and he's off playing tennis this afternoon so can't check for you.

He's made some interesting combinations over the years - Plum & Fig, Fig, Plum, Apricot, Peach & Apricot, Fig & Pineapple (or fig with pineapple in it). We have plum and fig trees that get loaded every year (and the neighbours have an apricot and peach tree next to our fence that gets loaded too).