The bigger room should cost more — but exactly how much more?
When one bedroom is clearly bigger than another, splitting the rent evenly quietly overcharges whoever takes the small room. But guessing the difference from floor area alone misses light, layout and noise. Fair Divider prices each room by what people actually prefer to pay — so the size difference is reflected fairly, to the cent.
It's tempting to split rent in proportion to floor area. But two rooms of the same size can be worth very different amounts: one gets morning light and a quiet courtyard, the other faces a busy street. Area is a starting point, not a fair answer — what matters is how much each room is worth to the people living there.
Enter each room and let every roommate choose the one they prefer at the current prices. The bigger room's price climbs only until the person who wants it still prefers it — and no one else would swap in. That is the fair size premium, found by preference rather than a formula, and the amounts always total the rent exactly.
Rent is €1,400 for a large 16 m² room and a small 9 m² room. Split evenly, each pays €700 — a clear win for whoever grabs the big room.
An envy-free split might price the large room at €820 and the small one at €580. The €240 gap reflects not just the extra floor space but everything the bigger room offers — and at those prices, neither roommate would trade. The total is still €1,400.