Radiator Size Calculator – Heat Every Room Perfectly
Choosing the right size radiator is important to ensure a warm, comfortable, and energy-efficient home.
Our Radiator Size Calculator provides you with any BTUs (British Thermal Units) needed to heat any room based on a variety of factors including room size, insulation, windows, and heat loss.
BTU/Watt Radiator Calculator
Why Radiator Size is Important?
- Radiator too small? Your room may never get warm enough.
- Radiator too large? You will waste energy and money.
The right size radiator fits your budget while keeping you comfortable.
How Radiator Sizing Works
We use the following to size radiators:
- Room dimensions (length x width x height)
- Insulation, Poor, Average, Good
- All windows (how many and what size)
- Room type, living room, bedroom, bathroom, etc.
- Outside wall exposure
Example Formula (Simplified):
BTU = Room Volume × Insulation Factor × Room Type Multiplier
Approximate BTU Guidelines by Room Type:
| Room Type | BTU per m³ (average insulation) |
|---|---|
| Living Room | 50–70 |
| Bedroom | 40–60 |
| Bathroom | 65–85 |
| Kitchen | 55–75 |
What are you going to need?
1. Measure your room length, width and height
2. Count number of outside walls
3. Note down window size and what the glazing is
4. Select insulation level
Output:
The calculator will tell you:
- Recommended BTU output
- Equivalent radiator size (watts)
- Recommendations for single/double panel radiators
Expert knowledge
1 watt = 3.412 BTUs
If you want to convert BTU to watts: BTU / 3.412
For colder climates, you can add 10%–15% to your BTU calculation
Pro Tips:
- For rooms with single-glazing add 20% BTU.
- Bathrooms, when you need a higher BTU, consider a ladder radiator or heated towel rail.
- Don't place furniture directly in front of radiators, this interferes with heating circulation.
Localized Output (Optional Feature)
Get radiator size indications based on UK standard room types, Metric or imperial and European or North American standards.
Conclusion:
- Don't guess your radiator size, calculate it!
- Our Radiator Size Calculator also provides you the wattage and KW result.
FAQ: Frequently Asked Questions
Q: what size radiator do I need for a 12x12 ft room?
A: about 5,000–6,000 BTUs depending on insulation and windows.
Q: How many BTUs to heat a bathroom?
A: usually 1,800–3,000 BTUs but if you include towel warmers add in some extra.
Q: Can I have multiple small radiators instead of one large radiator?
A: Sure, just so long as the accumulative BTU will match the BTU required.
