Overview
What Is a BTU Calculator?
This tool estimates the BTU (British Thermal Unit) capacity needed for an air conditioner or heater based on room square footage.
Calculate the AC/heater size needed for a room.
This tool estimates the BTU (British Thermal Unit) capacity needed for an air conditioner or heater based on room square footage.
Useful for selecting an appropriately-sized cooling or heating unit for a specific room.
Input the room's floor area.
The result updates automatically using standard estimation factors.
A common rule of thumb uses approximately 20 BTU per square foot for cooling, though this varies by room factors.
British Thermal Unit - a measure of heating/cooling capacity for HVAC equipment.
Yes, rooms with higher than standard ceilings need more BTU capacity than this basic square-footage estimate suggests.
Yes, hotter climates typically need more cooling capacity per square foot than this general estimate.
Yes, rooms with significant direct sun exposure typically need more cooling capacity.
No, calculations happen entirely in your browser.
When between sizes, rounding up slightly is often safer than undersizing, though extreme oversizing reduces efficiency.
This provides a general estimate that can apply to both, though specific heating and cooling needs can differ based on climate and insulation.
Yes, for whole-home systems or complex spaces, an HVAC professional's detailed calculation (Manual J) is recommended.
Yes, completely free with no sign-up required.