Room Size Calculator
Floor area, volume, recommended AC size, and capacity from your room's dimensions
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Quick summary
Enter a room's length, width, and ceiling height to get its floor area (sq ft and m²), volume, a recommended air-conditioner size in BTU, and roughly how many people it holds standing or seated. A 15×12 room is 180 sq ft, needs about a 3,600-BTU unit, and seats ~12. AC sizing uses ~20 BTU per square foot; add capacity for sunny rooms, high ceilings, or kitchens.
Reviewed by Simple Calculators TeamLast reviewed
How to use this calculator
- Enter the inputs requested by the calculator.
- Choose the units or options that match your situation and review the assumptions.
- Run or update the calculation to see the result.
- Review the result, breakdown, and formulas shown on the page.
- Check the inputs, units, dates, and limitations before saving or sharing the result.
Frequently asked questions
What size air conditioner do I need for my room?
A common rule is about 20 BTU per square foot of floor space, so a 180 sq ft room needs roughly 3,600 BTU. Add 10% for very sunny rooms, more for kitchens, and account for high ceilings — this calculator gives a baseline BTU from your floor area.
How do I calculate room volume?
Multiply length × width × height. A 15×12 room with 8 ft ceilings is 1,440 cubic feet. Volume matters for heating, ventilation, and airflow calculations where ceiling height counts, not just floor space.
How many people fit in a room?
For standing/reception layouts, plan about 5 sq ft per person; for seated/dining, about 15 sq ft. A 180 sq ft room holds ~36 standing or ~12 seated. Official occupancy limits are set by fire code and may be lower — treat these as planning estimates.
Does ceiling height affect air conditioner size?
Yes. Standard BTU-per-square-foot rules assume ~8 ft ceilings. Taller ceilings mean more air volume to cool, so bump the capacity up. If your ceilings are well above 8 ft, size up from the baseline this calculator provides.
Key terms
- BTU
- British Thermal Unit — the measure of an air conditioner's cooling capacity.
- Floor Area
- Length × width; the basis for AC sizing and occupancy.
- Volume
- Length × width × height; total air space, relevant for heating and ventilation.
Methodology, sources & limitations
This page shows the formula, assumptions, and limitations used for this estimate. Rates, thresholds, and other time-sensitive inputs can change, so verify them against the relevant official source before relying on a result.
For our review approach and the primary sources we consult, see the methodology and source policy. If you spot an outdated figure or formula, please contact us with a correction.