Determine the ideal heat output for your radiators. Input room dimensions, insulation quality, and window types to calculate the BTU or wattage needed. Prevents inefficient overheating or inadequate warmth.
Open Radiator Size Estimator → free, no sign-inRadiator Size Estimator is a free, browser-based tool on Doathingy.com. It lets you radiator size calculator directly in your browser — no software to install, no account required, and no files sent to any server.
Determine the ideal heat output for your radiators. Input room dimensions, insulation quality, and window types to calculate the BTU or wattage needed. Prevents inefficient overheating or inadequate warmth.
Everything runs locally on your device. Open the tool, do the task, done. It is designed for people who need results quickly, without a learning curve or a subscription.
Anyone who needs to radiator size calculator without friction. No technical knowledge required — if you can use a browser, you can use this tool.
No tutorials. No learning curve. The tool is designed to be immediately obvious to anyone.
Privacy first. Your files and data never leave your device. All processing happens locally in your browser — nothing is uploaded to a server.
Completely free. No trial periods, no premium tiers, no hidden costs. Use it as often as you need.
Zero friction. No account, no download, no browser extension. Works in any modern browser on desktop or mobile.
Built for one job. Radiator Size Estimator does exactly what it says and nothing more. No feature bloat, no distracting adverts.
What inputs do I need?
Room dimensions (length, width, height), insulation type, and window type.
Does it calculate in BTU or watts?
Both — results are given in BTU and watts.
Is this accurate enough to buy a radiator?
Yes — it provides a solid estimate for standard residential rooms. Always allow a 10-15% margin.
Does it account for different room types (conservatory, bathroom, etc.)?
Yes — different room types have different heat loss factors accounted for.
Is this free?
Yes — completely free.
Free. Instant. No sign-in. Open it now and get the job done.
Open Radiator Size Estimator on Doathingy.com →