Should my girlfriend have to chip for utility bills if she lives with?
Utility bills are different from rent. If your girlfriend is staying with you, sharing your room, then I agree that you still paying 1/4 of the rent is fair. However, you are now, between the two of you, using more than 25% of the electricity, hot water, heat and garbage collection. These expenses are not based on square footage, but on actual use. Unless your girlfriend claims to never turn the lights on when she is in the house, never plugs in an appliance, never uses the bathroom in any capacity, uses no hot water, doesnt turn the heat up when she is in the house, or ever creates any garbage while she is home, then, perhaps, she shouldnt have to pay her share of utilities. But I seriously doubt you can say she doesnt increase the use of utilities in your house by being there.