BTU and kW · metric or imperial
Air conditioner BTU calculator.
Size the room before comparing products. The model starts with an official capacity table, then shows every adjustment for height, glass, sun, insulation, people and appliances.
2
Example result — edit the roomPlanning range, not a professional cooling-load calculation.
Step 2 of 2Recommended cooling-capacity range
5,500–6,500BTU per hour1.6–1.9 kW cooling capacityAdjustments applied
No additional adjustment beyond the room-area capacity table.
Avoid “bigger is always better”
An oversized unit can cool quickly without controlling humidity well and may cycle more. An undersized unit may run continuously without reaching the target. Ask an installer to complete a room-by-room design calculation for fixed equipment.
How the calculation works
A published room-area table, with explicit planning adjustments.
The starting capacity comes from the ENERGY STAR room air-conditioner table. Heavy shade reduces it by 10%, strong sun adds 10%, each regular occupant above two adds 600 BTU/h, and a kitchen adds 4,000 BTU/h.
Better Home Climate then scales the base against an 8 ft ceiling and applies visible planning factors for insulation, window-to-floor area and appliance heat. The final recommendation is shown as a ±10% band and converted using 1 kW = 3,412.142 BTU/h.
What changes the result
Factors worth checking before you decide.
Room floor area and ceiling height.
Direct sun, orientation and the amount of glazing.
Insulation quality and uncontrolled air leakage.
Regular occupants and heat-producing equipment.
Kitchen cooking loads or a heavily equipped home office.
Outdoor design temperature, target temperature and adjacent spaces—items this simple model cannot fully capture.
Worked examples
See how the assumptions move the answer.
A 4 m × 3 m room, standard ceiling, average insulation, moderate glazing and two occupants.
A 6 m × 4 m room with poor insulation, substantial glass, strong sun, four occupants and moderate device heat.
The kitchen addition is applied after the room, height, insulation, window and sun calculations.
Common questions
Questions homeowners ask before spending.
How many BTU do I need for a bedroom?
It depends on floor area, ceiling height, glazing, sun, insulation, occupants and internal heat. A typical small bedroom may land near the lower end of common room-AC sizes, but use the calculator inputs and confirm fixed-system sizing with an installer.
How do I convert BTU/h to kW cooling capacity?
Divide BTU per hour by 3,412.142. The calculator shows both units and keeps the unrounded BTU-to-kW conversion behind the displayed range.
Should I buy the next size up?
Not automatically. Oversizing can cause short cycling and weaker humidity control, while undersizing can lead to long runtimes and poor comfort. Compare the published capacity range with the room and ask for a proper design calculation for fixed systems.
Does this replace an installer heat-load calculation?
No. It is a transparent planning estimate. It cannot model construction layers, air leakage, detailed solar gains, outdoor design temperature, ventilation or heat transfer between rooms.
Why does a kitchen need more cooling?
Cooking equipment adds a large intermittent heat load. ENERGY STAR's room-AC guidance adds 4,000 BTU/h for a kitchen, which this calculator applies visibly.
Sources and review trail
Transparent inputs, versioned model.
- Last reviewed
- 13 September 2026
- Model/version
- room-ac-btu-2026.09.1