About the BTU Calculator
HVAC sizing for a room. Use this free btu calculator to get instant results. All calculations run in your browser — nothing is sent to a server.
Frequently asked questions
What does this BTU Calculator do?
HVAC sizing for a room.
Is it free?
Yes — every calculator on Calcly is free, with no sign-up or account required.
Does it work offline?
The site is a Progressive Web App — after your first visit, most pages work without an internet connection.