Non prepared weight of quince will be about 310 g (about 2 medium quinces).
Before you start: Sterilise 2 x 250 ml jars (mine were bigger) and lids by washing thoroughly in hot soapy water (or take straight from dishwasher), fill jars with boiling water, empty and place on a baking tray. Bake in a preheated oven at 140°C for 20 mins and keep the jars there until ready to pot up. Place lids in a bowl and pour over boiling water, use tongs to lift out and drain on a clean tea towel or draining rack.