BTU Calculator
Estimate the cooling capacity (BTU/h) a room's air conditioner needs, or the heating a home needs, from its size and conditions.
Change the values and press Calculate to work out your own figures.
Cooling a room
Enter the room's size and conditions.
Show the working
- capacity = table × sun (0.9 shaded, 1.1 sunny) + 600 per person over 2 + 4,000 for a kitchen
Cooling, from the area
Enter the area and conditions.
Show the working
- capacity = table × sun (0.9 shaded, 1.1 sunny) + 600 per person over 2 + 4,000 for a kitchen
Heating a home
Enter the size, climate and insulation.
Show the working
- heat = area × 40–45 BTU per sq ft × 1
Heating, from the area
Enter the area, climate and insulation.
Show the working
- heat = area × 40–45 BTU per sq ft × 1
How to use it
Enter the room's size and conditions. Enter the area and conditions. Enter the size, climate and insulation. Enter the area, climate and insulation.
Lengths can be decimals, fractions or tape entries such as 12' 6 1/2" (in feet or inches). Prices are optional.
Key facts
cooling = table capacity × sun + 600 × (people − 2) + 4,000 for a kitchen heating = area × BTU per sq ft for the climate × insulation
Sizing
An oversized air conditioner cycles on and off and leaves the room clammy; an undersized one runs constantly. For a whole house, ask for a Manual J calculation.
Questions
What size air conditioner for a 300 sq ft room?
7,000 BTU/h in average sun with two people.
How many BTUs to heat 2,000 sq ft?
80,000–90,000 BTU/h in a moderate climate.
Formulas
cooling = table capacity × sun + 600 × (people − 2) + 4,000 for a kitchen heating = area × BTU per sq ft for the climate × insulation
Sources
Limitations
- Material densities are typical values (the midpoint of the commonly published range); real loads vary with moisture, grading and compaction, so check with your supplier or type in their density.
- Tank results are the geometric volume; real tanks have wall thickness and fittings.