How to split rent by room size

Splitting rent equally feels fair until one person has a bedroom twice the size of another’s. Then it feels like the person in the box room is subsidising the person with the bay window — because they are. Here is how to split rent by room size in a way everyone can check.

Three ways to split rent with different room sizes

Equal split. Everyone pays the same. Correct when the rooms are close in size and quality, and it has one big advantage: nobody needs to measure anything. If the difference between the largest and smallest room is a couple of square metres, stop here.

By bedroom area only. Add up the bedrooms and split the whole rent by each one’s share. Simple, but harsh: it treats the kitchen, living room and bathroom as if they belonged to whoever has the biggest bedroom. The person in the large room ends up paying for a bigger slice of a sofa everyone sits on.

Hybrid: common areas equal, private area by size. Split the flat’s floor area into two parts. The part everyone shares is split equally between people. The part only one person uses — their bedroom — is charged by area. This is the fair way to split rent with different room sizes in most flats, and it is the method the rest of this guide uses.

How the hybrid method works

You need three numbers: the total floor area of the flat (from the listing or the lease), the area of each bedroom, and the rent.

1. Work out the rent per square metre. Rent ÷ total floor area.
2. Price the common area. Total area minus all bedrooms is the shared space. Multiply by the rate and split it equally between everyone.
3. Price each bedroom. Bedroom area × the rate.
4. Each person pays their bedroom plus their equal share of the common area.

Every square metre of the flat is paid for exactly once, so the total always comes back to the rent.

A worked example: €1,800 for 90 m²

Ana, Leo and Sam rent a 90 m² flat for €1,800 a month. The bedrooms are 17 m² (Ana), 12 m² (Leo) and 10 m² (Sam) — 39 m² of private space, leaving 51 m² of kitchen, living room, hallway and bathroom.

• Rate: €1,800 ÷ 90 = €20 per m².
• Common area: 51 × €20 = €1,020, split three ways = €340 each.
• Bedrooms: Ana 17 × €20 = €340, Leo 12 × €20 = €240, Sam 10 × €20 = €200.

Compare that with splitting the whole rent by bedroom area alone: Ana’s 17 of 39 m² would make her pay €784.61, Leo €553.85 and Sam €461.54 (Ana’s figure takes the one cent of rounding so the total is exactly €1,800). That is nearly €105 a month more for Ana than the hybrid — for a living room she uses no more than anyone else.

If you would rather not do this by hand, the rent split calculator takes the rent and room sizes and gives you the amounts.

Adjustments for what area doesn’t capture

Square metres are a good proxy, not the whole story. Three things come up in almost every flat.

An en-suite bathroom

If one bedroom has its own bathroom, move that bathroom out of the common area and into that person’s private area. In the example, a 4 m² en-suite attached to Ana’s room makes her private area 21 m² and the common area 47 m². Rerun the four steps; the total still comes to €1,800.

A private balcony

A balcony is usually not counted in the flat’s floor area, and it is not worth the same as indoor space. The common approach is to count it at half its area: a 6 m² balcony off Leo’s room adds 3 m² to his private area. Agree the factor before you measure, not after.

Light, noise and the box room

The room over the bar, the one with no window, the one the boiler lives in. If the group agrees a room is worse than its size suggests, take a fixed amount off it — say €30 — and add it equally to the others. Keep it a round number everyone accepts; this is a judgement, not a calculation.

A couple sharing one room

When two people share a bedroom, they occupy one room but use the kitchen and the bathroom as two people. The fair version of the hybrid splits the common area per person and the bedroom per room.

Say Ana’s partner Max moves into the 17 m² room. The common €1,020 is now split four ways — €255 each — and the bedroom prices don’t change:

• Ana and Max: €340 for the room + 2 × €255 = €850 (€425 each)
• Leo: €240 + €255 = €495
• Sam: €200 + €255 = €455

€850 + €495 + €455 = €1,800. Leo and Sam both pay less than before, which is right: there are now four people sharing the same kitchen. If the couple pool their money, they can be a single member paying €850; if they keep separate finances, two members at €425 each.

Rent is one payment; the split is everyone’s

In most flats one person pays the landlord and the others pay them back. Record the full rent as one expense, paid by that person, split by exact amounts — €680 / €580 / €540 — and repeat it every month. In kisir that is one expense a month; it does not repeat on its own, so whoever pays the rent adds it when it goes out.

With Ana paying the landlord, the month ends like this:

What room size should not decide

Room size is a fair basis for rent. It is usually not a fair basis for bills: a bigger bedroom doesn’t make anyone shower longer or use more internet. Split utilities, internet and shared groceries equally, or by actual usage where it genuinely differs — see splitting utility bills with roommates and the broader guide to splitting rent and bills with roommates.

Write the numbers down once

The single most useful step is the last one: write the agreed amounts somewhere everyone can see, with the date they start. Rent splits do not go wrong because the maths was hard. They go wrong because six months later nobody remembers whether the balcony counted as half or not at all.