BTU Calculator
Find out exactly what size air conditioning unit you need for your room. Enter your details below for an instant recommendation.
Your Results
Room Volume
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m³
Recommended BTU
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BTU/hr
Equivalent kW
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kW
Our Recommendation
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This calculator provides an estimate. For an accurate assessment, we recommend a free on-site survey where we measure heat loads, check insulation, and factor in all variables specific to your property.
Or call us on 01273 455584
How BTU Sizing Works
Calculate Volume
We multiply length x width x height to get your room's volume in cubic metres.
Apply Factors
Sun exposure, insulation, windows, room type and occupants all affect the cooling load.
Get Your Size
The result tells you the BTU and kW rating to look for when choosing a system.
Quick Reference: Room Size Guide
| Room Size | Area (m²) | BTU Needed | kW Rating |
|---|---|---|---|
| Small Bedroom | 10-12 m² | 7,000-9,000 | 2.0-2.5 kW |
| Double Bedroom | 12-16 m² | 9,000-12,000 | 2.5-3.5 kW |
| Living Room | 20-30 m² | 14,000-20,000 | 4.0-6.0 kW |
| Large Open Plan | 30-45 m² | 20,000-30,000 | 6.0-9.0 kW |
| Garden Office | 8-15 m² | 6,000-10,000 | 1.8-3.0 kW |
| Conservatory | 12-20 m² | 12,000-22,000 | 3.5-6.5 kW |
Based on standard 2.4m ceiling height and average conditions. Use the calculator above for a more accurate figure.
Frequently Asked Questions
How do I calculate what size air conditioning I need?
Multiply your room's length x width x height (in metres) to get the volume. Then multiply by 337 to get the base BTU requirement. Adjust for sun exposure, insulation, windows, and room type. Our calculator above does this automatically—just enter your room details.
What is a BTU and why does it matter?
BTU stands for British Thermal Unit—a measure of cooling (or heating) capacity. A higher BTU rating means more cooling power. Choosing the correct BTU ensures your room cools efficiently without wasting energy or struggling to reach temperature.
What happens if I choose the wrong size unit?
An undersized unit will run constantly without reaching the desired temperature, increasing energy bills and wear. An oversized unit will short-cycle—turning on and off frequently—wasting energy and causing uneven temperatures. Correct sizing is essential for comfort and efficiency.
Is this calculator accurate enough to buy a system?
This gives a good estimate for planning purposes. However, a professional on-site survey considers additional factors like wall construction, glazing type, nearby heat sources, and airflow patterns. We offer free on-site surveys across Sussex to ensure you get the perfect system.
Need Help Choosing the Right System?
Our engineers will carry out a free on-site survey to calculate the exact cooling requirement for your space—no obligation.