If one bedroom is 20 m² with a window seat and another is 10 m² with a wardrobe wedged behind the door, an even rent split isn't neutral — it's a transfer from the small room to the big one. Splitting by floor area fixes it with a tape measure and one calculation.
Want the numbers instantly? Use our free bill split calculator to compare an income-based split with 50/50 in euros.
The core idea
You pay for the space you have exclusive use of. Kitchen, living room, hallway and shared bathroom are used by everyone, so they're shared equally and stay out of the calculation. Bedrooms are private, so they set the split.
That single principle is what makes this method easy to agree on: it's measurable, it doesn't require anyone to disclose their salary, and nobody has to argue about whose preference counts more.
The formula, step by step
- Measure each bedroom in square metres. Length × width. Use the usable floor area and ignore built-in cupboards for now.
- Add the bedroom areas together to get total private space. Do not include shared rooms.
- Find each room's share: room area ÷ total private area × 100.
- Apply the percentages to the full rent.
Your rent = (your bedroom m² ÷ total bedroom m²) × total rent
Worked example
Two bedrooms, 18 m² and 12 m², total rent €1,200. Total private space is 30 m².
| Room | Area | Share of private space | Rent |
|---|---|---|---|
| Room A | 18 m² | 60% | €720 |
| Room B | 12 m² | 40% | €480 |
| Total | 30 m² | 100% | €1,200 |
An even split would have been €600 each. The person in the small room was subsidising the large one by €120 a month — €1,440 a year.
Adjusting for the things area misses
Floor area doesn't capture everything. Apply flat monthly adjustments after the area calculation, and make sure they net to zero so the total still matches the rent.
- En-suite or private bathroom: +€40 to €80
- Balcony or private outdoor access: +€20 to €50
- Built-in wardrobe or extra storage: +€10 to €25
- No window, or a window onto a wall: −€30 to €60
- Street noise, or being next to the bathroom: −€20 to €40
- Room used as a walkthrough to a shared space: −€20 to €40
Don't chase a perfect number. The test is whether everyone can say the arrangement is reasonable, not whether the maths is provably optimal.
What about very unequal rooms?
When one bedroom is more than roughly twice another, pure area splitting can produce a share the small-room occupant thinks is still too high — because a 9 m² room isn't half as liveable as an 18 m² one, it's barely liveable. In that case, blend the methods: take the average of the even split and the area split. It softens the extremes and usually lands where both people already felt it should.
Simplifying after move-in
Once the split is agreed, freeze it. Recalculating every time someone repaints or swaps rooms creates more friction than it removes. Revisit only when someone moves out, someone changes rooms, or the rent itself changes — and write the agreed figures down where everyone can find them.
Then keep the ongoing costs organised: uneven rent, even utilities, and a fixed monthly settle-up date. What kills flatshare finances isn't the rent formula, it's six weeks of untracked shared shopping.
Frequently asked questions
Should shared rooms be counted at all?
Not in the split. Everyone uses them equally, so including them just moves every share closer to even and defeats the purpose.
How exact do the measurements need to be?
Rounding to the nearest half metre is plenty. Precision to the centimetre changes the rent by a euro or two and invites arguments over nothing.
Can we combine room size with income?
Yes — some households set the rooms by area, then adjust once for a large income gap. Just agree the order of operations and record the result. See splitting rent based on income.
What if the biggest room is shared by a couple?
Charge that room for its area plus a shared-space premium, then let the couple divide their share between themselves. Details: how to split rent when a couple shares with roommates.
Keep the whole flat in one ledger
SharedNest supports custom split shares per person, so unequal rent, even utilities and one-off shared purchases all sit in the same running balance. Start free while we're building.
Also useful: splitting rent with roommates fairly
