You can check whether your luggage complies with the permitted dimensions (56cm x 40cm x 25cm) for transportation as hand luggage by using the sizers you will find in the check-in area at all airports. If it is too big, you will have to check it in.

Remember also that the maximum weight of hand luggage on Iberia Group flights is 10 kg in Economy class and 14 kg if you travel in Business.