About

BTUcalc is a small set of free BTU and air-conditioner size calculators. We built it because most "what size AC" advice online is either a vague chart or a lead form that wants your email. Here the math runs entirely in your browser; nothing you type is uploaded or stored.

Our calculators are reviewed by a working HVAC technician, Mike R., for sensible defaults and plain-English explanations. We are not an equipment dealer and we do not sell units — we just want the number to be honest and free.