BTU Calculator
Estimate the heating and cooling BTUs a room needs — plus tons of cooling and a suggested air-conditioner or mini-split size — based on area, climate, and sun exposure.
This is a rule-of-thumb estimate. A full Manual J load calculation that accounts for insulation, windows, and air sealing is recommended before buying or sizing equipment.
How to Size Heating & Cooling by BTU
A BTU (British Thermal Unit) measures the heat an HVAC system can add or remove per hour. The classic rule of thumb is roughly 20 BTU per square foot for cooling, then adjusted up for tall ceilings, sunny exposures, extra occupants, and kitchens. To convert the cooling load to tons, divide by 12,000 — one ton of cooling equals 12,000 BTU/hr.
Heating needs depend heavily on climate, so this calculator multiplies your floor area by a BTU-per-square-foot factor that rises from hot zones (about 30) to very cold zones (about 60). These shortcuts are great for ballpark planning, but the most accurate sizing comes from a Manual J load calculation that models your specific insulation, windows, and air leakage.
Frequently Asked Questions
How many BTU do I need to cool a room?
A common rule of thumb is about 20 BTU per square foot of living space. A 300 sq ft room needs roughly 6,000 BTU, adjusted up for tall ceilings, lots of sun, extra people, or kitchen appliances.
What size air conditioner do I need for 500 sq ft?
At about 20 BTU per square foot, 500 sq ft needs roughly 10,000 BTU of cooling. A 12,000 BTU (1-ton) unit is the nearest standard size, with the exact figure depending on ceiling height, sun, and occupants.
How do I convert BTU to tons of cooling?
Divide the cooling BTU per hour by 12,000, because one ton of air-conditioning equals 12,000 BTU/hr. For example, 24,000 BTU equals 2 tons of cooling capacity.
Turn Your Measurements Into a Real Floor Plan
Once you know your dimensions, generate a labeled, to-scale floor plan in seconds — then export it to DXF or build it in 3D. No CAD experience needed.
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