Rent split calculator by room size

Enter the full rent and the square footage of every room, and the calculator assigns each room the same proportion of rent as its proportion of the combined private room area. Results are rounded to cents without losing or inventing money, so the individual shares always add back to the stated total. The method focuses only on bedroom size; shared spaces, amenities, parking, and occupancy can be discussed separately.

Measure the private rooms consistently

Begin with the same measurement rule for every bedroom. Measure the usable floor area inside each private room, using interior wall-to-wall dimensions and the same unit throughout. This calculator expects square feet, so convert any measurements taken in another unit before entering them. Include closets only if the household agrees that they belong to the private room, and apply that choice consistently to all rooms. Do not add kitchens, living rooms, shared bathrooms, corridors, or other common areas, because those spaces are available to everyone and would not distinguish one room from another. Give every room a clear name so the result remains understandable when it is copied into a household agreement. A room may have zero square feet in the data, although that room will receive a zero size-based share; however, the combined area of all rooms must be greater than zero. Accurate, consistently defined measurements matter more than false precision, so rounding each room to a sensible whole or decimal square-foot value is usually sufficient.

Understand the proportional calculation

The calculator first adds all room areas to obtain the total private square footage. It then divides each room's area by that total to obtain the room's percentage share. Multiplying that percentage by the total rent produces the unrounded allocation. Currency introduces an extra detail: several exact allocations can contain fractions of a cent, while an actual payment must use whole cents. The calculator floors the provisional allocations to cents and distributes any remaining cents to rooms with the largest discarded fractions. If two fractions are equal, their original input order provides a stable tie-breaker. This largest-remainder method ensures that the displayed room payments add exactly to the rounded total rent, rather than being a cent short or over because every value was rounded independently. The returned percentage is descriptive and shown to six decimal places, while the rent share is the cent-accurate amount to pay. Running the same input again always returns the same allocation because the calculation uses no external data or changing state.

Use the result as a fair starting agreement

Room area is a simple, auditable basis for a sublet or shared lease, but it does not capture every source of value. After calculating the size-based split, discuss whether private bathrooms, natural light, noise, storage, parking, furnishings, or unequal access to shared facilities justify an agreed adjustment. If more than one person occupies a room, the household may also decide to separate private-room value from the cost of common areas and utilities. Record any adjustment explicitly instead of changing the measurements, because preserving the original proportional result makes the negotiation easy to review later. The output uses no currency conversion: a total entered in dollars produces dollar-denominated shares, while a total entered in another currency remains in that currency. For recurring payments, keep the room names, measurements, total rent, calculator result, and any negotiated modifications together in writing. Recalculate whenever the landlord changes the rent, rooms are remodeled, or occupants agree on a different measurement convention. API requests cost $0.002; the browser calculation can be used for an immediate comparison before anyone commits to a payment arrangement.