Heating BTU Calculator
Estimate heating BTUs from room size and climate.
Enter your room's square footage and choose your climate to estimate the heating capacity you need, in BTUs per hour. It's a quick guide — insulation quality, ceiling height, and window area all shift the real number.
How it works
Heating demand depends heavily on climate. As a rough guide, mild climates need about 30 BTU per square foot, moderate climates about 45, and cold climates 60 or more. Multiply your area by the factor for your climate.
Frequently asked questions
How many BTUs do I need to heat a room?
Multiply the area by a climate factor — about 30 BTU/sq ft in mild climates, 45 in moderate, and 60 in cold. A 400 sq ft room in a moderate climate needs about 18,000 BTU.
How many BTUs per square foot for heating?
Roughly 30 to 60 BTU per square foot depending on climate, insulation, and ceiling height.
Does insulation change the BTUs needed?
Yes — well-insulated, tightly sealed rooms need fewer BTUs, while drafty rooms with lots of glass need more.
Is this calculator free and private?
Yes. Every CubicCabin calculator runs entirely in your browser, so the numbers you enter are never uploaded or stored. There's no sign-up, no limits, and it keeps working even if you lose connection after the page loads.