BTU Calculator

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Find the right air conditioner or heater size for any room — enter your room dimensions, sun exposure and occupancy to get cooling BTU, tons and recommended AC size.

m
m
m
Cooling needed – BTU/h
Tons of cooling –
Recommended AC –
Heating needed –
Estimates use ~20 BTU/h per sq ft for cooling with adjustments for sun, ceiling height, occupants and kitchens (1 ton = 12,000 BTU/h). Confirm with an HVAC professional for installation.

About BTU Calculator

The BTU calculator sizes the air conditioner or heater a room needs. Enter the room’s length, width and ceiling height, the number of regular occupants, the sun exposure and whether the space is a kitchen, and it returns the cooling requirement in BTU/h, the equivalent tons of cooling and a recommended AC size, plus a heating estimate.

The estimate starts from a rule of thumb of roughly 20 BTU per hour per square foot for cooling, then adjusts for tall ceilings, sunny or shaded exposure, extra occupants and the heat load of a kitchen. One ton of cooling equals 12,000 BTU/h, which is how larger systems are labeled.

Correct sizing matters both ways: an undersized unit runs constantly without reaching temperature, while an oversized one short-cycles and dehumidifies poorly. Use this free calculator to shortlist equipment, then confirm the final choice with an HVAC professional before installation.

How to use BTU Calculator

  1. Choose metric or imperial units and enter the room length, width and ceiling height.
  2. Set the number of regular occupants.
  3. Pick the sun exposure — shaded, average or sunny — and tick the kitchen option if it applies.
  4. Read the cooling BTU/h, tons, recommended AC size and the heating estimate.

Frequently asked questions

A common cooling baseline is about 20 BTU per hour per square foot. This calculator applies that figure and then adjusts for ceiling height, sun exposure, occupancy and kitchens, which is why two same-sized rooms can need different units.

One ton equals 12,000 BTU per hour of cooling capacity. A room needing 18,000 BTU/h therefore calls for a 1.5-ton unit — the calculator shows both figures side by side.

No. An oversized unit cools the air quickly but short-cycles before removing humidity, leaving the room clammy and wearing the compressor. Matching capacity to the calculated load gives better comfort and efficiency.

Ovens, stoves and refrigerators add significant heat to the room, so the calculator raises the cooling load when you mark the space as a kitchen.

Treat it as a solid first estimate. Insulation quality, window area, climate and duct layout also affect the load, so have an HVAC professional confirm the size before purchasing or installing equipment.
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