BTU Calculator
Estimate the cooling BTU and tons an air conditioner needs for a room from its size, ceiling height, sun exposure, occupants, and whether it’s a kitchen. Calculates in your browser.
Cooling capacity needed
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Show the math
Start from about 20 BTU per square foot, then adjust for the room:
btu = area × 20 × (ceiling ÷ 8) × sun factor
+ 600 per extra occupant over 2, + 4,000 for a kitchen
This is a quick rule-of-thumb estimate, not a full Manual J load calculation. One ton of cooling equals 12,000 BTU per hour. All math runs locally in your browser.
What this does
A BTU calculator estimates the cooling BTU and tons an air conditioner needs for a room from its size, ceiling height, sun exposure, occupants, and use.
How to use it
- Enter the room size.
- Set the ceiling height and sun exposure.
- Add the occupants.
- Read the BTU and tons.
How it works
A rule of thumb is about 20 BTU per square foot, adjusted for ceiling height, sun, occupants, and heat-producing rooms. It is not a full Manual J.
1 ton = 12,000 BTU/hour
Understanding your result
This is a rule-of-thumb estimate, not a full Manual J load calculation, and bigger is not better: an oversized air conditioner short-cycles, cools the air without removing humidity, and leaves the room clammy. Use the figure to find the right size band, then lean toward correct sizing rather than rounding up to the next large unit.
Example
A 300 sq ft room needs roughly 6,000 BTU, about half a ton.
Sources & methodology
Last updated .
Frequently asked questions
How many BTU do I need per square foot?
A rule of thumb is about 20 BTU per square foot of living space, adjusted for ceiling height, sun, occupants, and heat-producing rooms.
How many BTU are in a ton?
One ton of cooling equals 12,000 BTU per hour. The tool reports both so you can match a unit’s rating.
Is this a Manual J load calculation?
No, it is a quick rule-of-thumb estimate. A full Manual J accounts for insulation, windows, and climate in detail.
Do you store my numbers?
No. Everything is calculated locally in your browser.
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