It's not just at Girona. Last year I flew from Malaga to Prestwick via Stansted with Easyjet and Ryanair. At Malaga my small suitcase weighed 17kg but at Stansted it weighed only 14kg!! My advice to anyone who gets charged for overweight luggage is to get it weighed more than once. I don't know what the law is in Spain but in the UK the scales will have to be checked regularly.