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.
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.
Rooms you can plan with this tool
Real-room inspiration that uses this tool's outputs.
kitchen
Industrial loft kitchen — concrete floor, blackened steel cabinets, oak island
industrial, modern
office · living
Modern home library — floor-to-ceiling shelving, reading chair, library lamp
modern, minimalist, traditional
living · office
Modern reading nook — single lounge chair, articulating sconce, single shelf
modern, minimalist