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Cost Allocation by Square Footage Calculator

Enter the total cost, the unit's area and the total area to allocate the cost by square footage.

How it is calculated

Each unit pays in proportion to the floor area it occupies: share = total_cost × (unit_sqft ÷ total_sqft). total_cost is the bill to be divided (any currency and any period), unit_sqft is the area of the unit being billed and total_sqft is the combined area of all units sharing the cost, both in square feet. The tool also reports the rate per square foot, total_cost ÷ total_sqft, and the unit's percentage share of the building. If the unit area is zero or negative, or larger than the total area, no result is produced. Which areas count (usable, rentable, common space) is set by your lease or bylaws, so use the same measurement for both area figures.

Worked example

A building has a 12,000 annual maintenance bill and 15,000 sq ft in total. Your unit is 1,800 sq ft. Step 1: your fraction of the building is 1,800 ÷ 15,000 = 0.12, shown as 12.00%. Step 2: the rate per square foot is 12,000 ÷ 15,000 = $0.80 / sq ft. Step 3: your allocated share is 12,000 × 0.12 = $1,440.00. Multiplying 1,800 sq ft by the 0.80 rate gives the same figure.

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Common mistakes

  • Mixing area definitions, for example your unit in usable square feet but the building total in rentable square feet. The share will be wrong.
  • Leaving vacant units out of the total area. If vacant space still counts under your lease, the total must include it, otherwise occupied units overpay.
  • Entering square metres for one area and square feet for the other.
  • Using the building's total area when the cost only serves part of it, such as a lift that only some floors use.
  • Entering a unit area larger than the total, which gives no result; usually one figure has a typo.

Sources

About this calculator

Splitting a shared cost by square footage is the standard method for common-area maintenance (CAM) charges, shared utility bills, and joint repair costs in commercial leasing, multi-tenant buildings and condo/HOA arrangements: each unit pays a share proportional to how much of the total floor area it occupies — Unit share = Total cost × (Unit area / Total area).

This pro-rata approach is considered the fairest default when usage can’t be metered individually, since a larger unit is assumed to draw proportionally more heating, cooling, cleaning and shared-service resources than a smaller one; commercial leases typically spell out this formula explicitly under a CAM or “operating expense” clause. Property managers, landlords and HOA boards use it to bill tenants or owners transparently and defensibly. Divide a shared bill fairly by floor area: enter the total cost, one unit's area and the building's total area, and that unit's share is shown.

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Comments (1)

  • Editorial team

    Before splitting a shared bill, check which floor area your lease or bylaws use: usable, rentable or gross. The tool only compares the two numbers you type, so the share is only as fair as those measurements. One detail: if you enter both areas in square metres, the share and the allocated amount stay correct, but the per-square-foot line then really means per square metre. Which shared charge is hardest to split in your building?

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