BTU Calculator

BTU stands for British Thermal Unit. It is the amount of energy needed to raise one pound of water by one degree Fahrenheit. HVAC systems use BTUs to measure heating and cooling power.

For cooling, a good starting point is 20 BTUs per square foot. A 300 sq ft room needs about 6,000 BTUs. This number goes up or down based on ceiling height, sunlight, insulation, and climate.

The Room AC / Cooling tab sizes a single-room air conditioner. It asks for room details like sun exposure, occupants, and room type. The General Heating & Cooling tab estimates BTUs for a whole home or large space and can calculate both heating and cooling loads.

Divide the BTU number by 12,000. One ton of air conditioning equals 12,000 BTUs per hour. For example, 24,000 BTUs equals 2 tons.

Kitchens have stoves, ovens, and other appliances that give off a lot of heat. The calculator adds 4,000 BTUs to account for this extra heat load so your AC can keep up.

Taller ceilings mean more air volume in the room. More air takes more energy to cool or heat. The calculator uses 8 feet as the standard and adjusts up or down from there.

Each person beyond the first two adds 600 BTUs. The human body gives off heat, so more people in a room means more cooling is needed.

Yes. Every dimension field has a toggle to switch between feet and meters. The calculator converts everything internally so the result is accurate no matter which unit you use.

An oversized AC turns on and off too quickly. This is called short cycling. It wastes electricity, wears out the compressor faster, and leaves the air humid because the unit does not run long enough to remove moisture.

An undersized AC will run constantly and still not cool the room enough. It will struggle on hot days, drive up your energy bill, and shorten the life of the unit.

Yes. Poor insulation can increase your BTU needs by 15% or more. Good insulation can lower them by about 10%. Well-insulated walls, windows, and attics keep conditioned air inside.

A room with heavy direct sunlight absorbs more heat, so it needs about 10% more BTUs. A heavily shaded room stays cooler on its own and needs about 10% fewer BTUs.

Pick Cool / Northern for places with mild summers. Pick Moderate for average climates. Pick Hot / Southern for warm areas and Very Hot / Desert for places with extreme summer heat above 100°F regularly.

It multiplies the room's air volume by the temperature difference between indoors and outdoors, then applies a heat transfer constant of 0.133. It also factors in insulation quality. A bigger temperature gap means more heating BTUs are needed.

The temperature delta is the difference between your desired indoor temperature and the coldest (or hottest) outdoor temperature. For example, if you want 70°F inside and it gets down to 30°F outside, the delta is 40°F.

In most climates, heating requires more BTUs than cooling for the same space. This is because winter temperature differences are usually larger than summer ones. The General tab lets you compare both side by side.

If you do not know your exact room dimensions, switch to the Range mode. It lets you pick a common size bracket like 150–250 sq ft. The calculator uses the midpoint of that range for the estimate.

Yes. When you enter both the room width and length, the calculator multiplies them and fills in the room size automatically. You can still override it by typing a different number.

This calculator gives a strong estimate based on industry rules of thumb. It is a great starting point for shopping. For a full home HVAC install, a professional should do a Manual J load calculation that accounts for windows, duct losses, and other details.

A 500 sq ft room with standard 8-foot ceilings typically needs about 10,000 BTUs for cooling. Adjustments for sun, climate, and insulation may push this higher or lower.