Why split by room size
An equal split is easy to explain, and it is perfectly reasonable when the rooms are about the same. When one bedroom is twice the size of another, though, the person in the larger one gets a lot more for the same money. Splitting by room size lets the larger room pay more and the smaller room pay less, without anyone having to argue about it each month.
It works best when incomes are similar and the main difference between roommates is the space they have. If incomes differ a lot as well, you may prefer to split rent by income, or to combine the two ideas.
The formula
Measure each bedroom, add the sizes together, and divide each room by the total. Multiply that fraction by the rent.
Your share = (your room’s size ÷ all bedrooms added together) × rent
Only the bedrooms are counted, because the shared areas belong to everyone. If you want shared space to count, use the hybrid method below.
A worked example
Three roommates share an apartment that costs $1,800 a month. The bedrooms are 180, 140 and 120 square feet, 440 in total.
| Room | Size | Share | Pays | Equal split |
|---|---|---|---|---|
| Large | 180 sq ft | 40.9% | $736.36 | $600.00 |
| Medium | 140 sq ft | 31.8% | $572.73 | $600.00 |
| Small | 120 sq ft | 27.3% | $490.91 | $600.00 |
| Total | 440 sq ft | 100% | $1,800.00 | $1,800.00 |
The exact shares are $736.3636, $572.7273 and $490.9091. Rounded down to the cent they add up to $1,799.98, so the two left-over cents go to the largest remainders (the medium and small rooms) and the total is exactly $1,800.00. Halfup does it the same way every time.
The 50/50 hybrid
Everyone uses the kitchen, living room and bathroom equally, so some people feel that only part of the rent should depend on bedroom size. The hybrid method splits the rent in two halves: one half equally, for shared space, and one half by bedroom size.
With the same $1,800 rent, the first $900 is $300 for each person. The second $900 is split by room size: $368.18, $286.36 and $245.46. The three totals are $668.18, $586.36 and $545.46, which add up to exactly $1,800.00. The gap between the largest and smallest room shrinks from about $245 to about $123.
You can use any ratio, for example 70/30. What matters is that everyone agrees before choosing a room.
Beyond square footage
Size is only one thing that makes a room worth more or less. Before you settle the numbers, talk through the others:
- An attached bathroom, a balcony or a walk-in closet.
- Natural light, a view or a quieter side of the building.
- Whether the room is a proper bedroom or a converted space.
- Whether two people live in it.
A simple way to include these is a fixed premium, for example an extra $50 a month for the room with its own bathroom, taken off the others. Once the rent shares are set, the other shared costs can follow the same rule or a different one: see fair ways to split bills between roommates.
Whichever way you go, write it down and revisit it if someone moves rooms or a new person joins. Halfup keeps the rule you choose and applies it to every bill, and it never moves money: you pay each other as you already do and record it.
Common questions
Should shared spaces count when splitting rent by room size?
Usually not in the bedroom measurement, because everyone uses the living room, kitchen and hallway. The hybrid method handles this: split part of the rent equally for shared space and part by bedroom size.
How do I measure a room?
Multiply the length by the width of the usable floor area, in square feet or square metres. Use the same unit and the same method for every room, and agree whether to count closets or an attached bathroom.
What if one room has its own bathroom?
Treat it as a premium. Either add a fixed amount to that room’s share, or count the bathroom’s floor area in that room. Agree the premium before anyone picks a room.