Room BTU Calculator
Size a mini-split, window unit, or space heater for one room — by area, ceiling height, sun, and occupancy — and get the nearest real unit size to buy.
Sizing a window unit or mini-split is where most people overshoot — and an oversized air conditioner actually cools worse, leaving a room cold and humid. This calculator gives the right single-room load from area, ceiling height, sun, and occupancy, then snaps to the nearest real unit size.
For a whole-home central system use the HVAC Sizing tool, and estimate the running cost with the Utility Cost Estimator.
FAQ
- How many BTUs do I need for a room?
- Start at about 20 BTU per square foot, then adjust for ceiling height, sun exposure, how many people use the room, and whether it's a kitchen. This calculator does that and rounds to the nearest common mini-split or window-unit size.
- Is bigger always better for an air conditioner?
- No — oversizing is a common mistake. A unit that's too large cools the air fast but shuts off before removing humidity, leaving the room cold and clammy and wearing the compressor with frequent cycling. Match the load, don't exceed it.
- How is this different from the HVAC Sizing tool?
- This sizes a single room for a window unit, mini-split, or space heater. The HVAC Sizing tool sizes a whole-home central system using a fuller load calculation. Use this for one room, that for the whole house.
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