Radisize: Radiator Calculator

Size radiators room-by-room in seconds. Get clear BTU/kW requirements and export professional PDF reports — all calculated offline.

Radisize is the modern way to calculate the correct radiator size for every room in your home or project. Whether you are renovating, upgrading your heating system, or working professionally, Radisize gives you clear BTU and kW requirements based on real room details.

Simply add a property, enter each room’s dimensions, glazing, walls, and floor materials, and Radisize automatically calculates the radiator output needed at either ΔT35 or ΔT50. All calculations are done offline on your device.

FEATURES

• Room-by-room radiator sizing Enter room type, dimensions, glazing and materials to get accurate BTU and kW requirements.

• Multiple properties Create and manage as many properties as you need for your home, rentals, or client work.

• Guided room setup A simple three-step wizard makes entering each room’s details quick and easy.

• Accurate BTU and kW outputs Calculations use realistic heat-loss logic and your preferred radiator rating (ΔT35 or ΔT50).

• Customisable settings Choose metres or feet, set your default ΔT, adjust the safety factor, and pick light, dark or system theme.

• Professional PDF reports Export clean, organised reports for an entire property containing every room’s radiator requirement. Ideal for planning, quotes and documentation.

• Offline-first No account, no internet, no data sent anywhere. Everything is calculated locally on your device.

WHO IT'S FOR

Homeowners and DIY renovators Plan heating upgrades confidently, understand your home’s requirements, and choose the right radiators without guesswork.

Heating engineers and installers Get quick on-site estimates, generate structured PDF reports, and keep multiple properties organised.

WHAT RADISIZE CONSIDERS

• Room dimensions (metres or feet) • External wall count • Wall construction type • Floor and ceiling types • Glazing area and window type • Safety factor • ΔT35 or ΔT50 radiator rating

Every detail is used to provide a more reliable radiator requirement.

Radisize offers a clean and modern design that makes complex heating calculations simple and approachable for everyone.

No subscriptions. No login. No hassle. Just fast, clear radiator sizing.

Use of this app is subject to Apple’s Standard Licensed Application End User License Agreement (EULA), available in the App Store under “License Agreement” and at https://www.apple.com/legal/internet-services/itunes/dev/stdeula/ Download Radisize today and find the right radiator size for every room.

Disclaimer: Radisize provides estimation guidance only. Results are approximate and do not replace professional design or safety advice. Always consult a qualified heating engineer and follow local building regulations before purchasing or installing any heating equipment.