£660 a month. That is the gap between the biggest and smallest room in one £2,400 flat if you score the rooms with a points system, against £0 if you split it equally. To split rent by room size is the simplest fair fix, but it is not the only one, and the three common methods give three different answers.
So instead of describing the methods in the abstract, we ran one flat through all of them. Same rent, same rooms, same three people. You can watch the numbers move.
The flat we will use
Three flatmates share a flat that costs £2,400 a month. We will call them Ines, Tom and Priya.
- Ines: 18 m², private en-suite bathroom, the quiet back of the flat.
- Tom: 12 m², shares the main bathroom, average light.
- Priya: 9 m², shares the main bathroom, one small window onto the road.
The kitchen and living room are shared by all three, so we leave them out of the maths and treat the whole rent as a price for the three bedrooms. More on that choice further down.
Method 1: split rent by room size (floor area)
Add up the bedroom areas, work out each person's share, and multiply by the rent. Here the total is 39 m², so Ines has 18 of 39, Tom 12 of 39 and Priya 9 of 39.
It is easy to explain and hard to argue with, because anyone can check a tape measure. Measure the rooms yourselves rather than trusting the listing, which often rounds up or includes cupboards and corridors.
| Flatmate | Area | Share | Pays |
|---|---|---|---|
| Ines | 18 m² | 46.2% | £1,107.69 |
| Tom | 12 m² | 30.8% | £738.46 |
| Priya | 9 m² | 23.1% | £553.85 |
The three amounts add up to exactly £2,400.00. The weak spot is that area ignores everything else: Ines's en-suite counts for nothing, and Priya's noisy window costs her nothing extra.
Method 2: split by features, from an equal starting point
Start with an equal share, which is £800 each. Then agree a fixed amount for each real difference, with the rule that every extra pound one person pays comes off someone else's bill.
The group decides that the en-suite and extra space are worth £150 a month, and that Priya's small, noisy room deserves £150 off. Tom is the baseline, so he stays at £800.
| Flatmate | Equal share | Adjustment | Pays |
|---|---|---|---|
| Ines | £800 | +£150 | £950 |
| Tom | £800 | £0 | £800 |
| Priya | £800 | -£150 | £650 |
The gap between Ines and Priya is £300. This method feels natural and the numbers are round. The risk is that the adjustments are guesses, so the loudest flatmate can talk the group into them.
Method 3: a points system for unequal rooms
Score each room from 1 to 5 on the things that matter to your group: size, light, bathroom, noise and storage. Add the points, then divide the rent by the total. Everyone scores every room, and you average the scores or agree them together.
Our flatmates' agreed scores add up to 40 points, so each point is worth £60 (£2,400 divided by 40).
| Flatmate | Size | Light | Bathroom | Noise | Storage | Total | Pays |
|---|---|---|---|---|---|---|---|
| Ines | 5 | 4 | 5 | 3 | 2 | 19 | £1,140 |
| Tom | 3 | 3 | 2 | 3 | 2 | 13 | £780 |
| Priya | 2 | 2 | 2 | 1 | 1 | 8 | £480 |
Now the gap is £660. Priya pays £480 and Ines £1,140, and Tom actually pays a little less than an equal share.
The three methods side by side
| Flatmate | Equal | By area | By features | By points |
|---|---|---|---|---|
| Ines | £800.00 | £1,107.69 | £950.00 | £1,140.00 |
| Tom | £800.00 | £738.46 | £800.00 | £780.00 |
| Priya | £800.00 | £553.85 | £650.00 | £480.00 |
| Gap, top to bottom | £0 | £553.84 | £300.00 | £660.00 |
Notice what happened. Tom pays between £738 and £800 whatever you choose, but Ines and Priya swing by hundreds of pounds. The method matters most to the people at the two ends.
Which method should you pick?
Use floor area when the rooms look alike apart from size, or when you want the least arguing. Use features when a couple of differences are obvious, such as one en-suite. Use points when several things differ at once and people feel strongly.
If you cannot agree, run all three and take the middle number for each person. It is not elegant, but a rent everyone helped choose is a rent nobody resents.
What about the kitchen, living room and bills?
Shared rooms are used by everyone, so most flats leave them out of the weighting. Some groups instead split a slice of the rent equally for shared space (say £600 of the £2,400) and weight only the rest. Either is fine if you write it down.
Bills are different. Gas, electricity and broadband usually go equally, and the rules change if someone arrives or leaves part-way through the month. See how to split utility bills when someone moves in mid-month.
Deposits follow the rent: if Ines pays 46 percent of the rent in method 1, she usually puts in 46 percent of the deposit. Check local rules on how deposits must be held, because they vary.
Write the agreement down
The best split is the one you all agreed to before anyone signed. Put the method, the amounts and what happens when someone leaves in your roommate agreement template. Here is a sentence you can paste into the group chat.
"Let's split the rent by [area / features / points] using the numbers in this table. If someone moves out or a room changes, we re-run it together and everyone has to agree before the new amounts start."
Evens is built for this kind of flat. In a home group you can give each person their own share of a cost, so a bill or the rent follows your agreed split, and monthly bills repeat on their own.
Frequently asked questions
Is it fair to split rent by room size?
It is fair when the rooms differ mostly in size and the shared spaces are the same for everyone. If one room also has an en-suite, better light or less noise, add those differences through features or points.
How do you calculate rent by square metre?
Add up the bedroom areas, divide each room's area by the total, and multiply that share by the rent. For example, 12 m² out of 39 m² is 30.8 percent, which is £738.46 of £2,400.
Should shared rooms count in the room-size split?
Usually not, because everyone uses the kitchen and living room equally. If you want to include them, split a fixed slice of the rent equally and weight only the rest.
What if a flatmate refuses an unequal split?
Show them the numbers from all three methods and measure the rooms together. Many people agree once they see that the smallest room is subsidising the biggest under an equal split.
What happens to the split if someone moves out?
Re-run the same method with the new group, and agree this in advance. If a replacement takes the same room, the amounts can simply stay the same.