Each time you calculate, a new line is added below. Use CSV or PDF download to keep records or share with clients.
| # | Room size (m) | Area (m²) | Volume (m³) | Room type | Climate | Cooling (BTU/h) | Unit (tons) | Suggested size |
|---|---|---|---|---|---|---|---|---|
| 1 | 5.0 × 4.0 × 2.7 | 20.0 | 54.0 | Bedroom | Moderate | 14000 | 1.17 | 1.5 ton |
Example room sizes and approximate cooling needs
These examples assume average insulation, standard ceiling height and moderate climate. Always adjust for your own conditions using the calculator above.
| Room type | Dimensions (m) | Area (m²) | Approx BTU/h | Approx unit size (tons) |
|---|---|---|---|---|
| Small bedroom | 3.0 × 3.0 | 9.0 | 7000–9000 | 0.75 |
| Medium bedroom | 4.0 × 3.5 | 14.0 | 9000–12000 | 1.0 |
| Living room | 6.0 × 4.0 | 24.0 | 16000–21000 | 1.5 |
| Open-plan lounge | 7.0 × 5.0 | 35.0 | 24000–30000 | 2.0–2.5 |
Formula used for cooling capacity
This calculator uses a rule-of-thumb approach based on floor area in square feet, adjusted for ceiling height, climate, insulation, sun exposure, occupancy and room usage.
- Convert metric floor area to square feet: Area(ft²) = Area(m²) × 10.7639.
- Apply a base cooling rate of 20 BTU/h per ft² for typical residential rooms.
- Adjust for ceiling height: Height factor = actual height / 2.7 m.
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Apply correction factors:
- Climate factor: cool 0.9, moderate 1.0, warm 1.1, hot 1.2.
- Insulation factor: good 0.9, average 1.0, poor 1.1.
- Sun exposure factor: low 0.95, medium 1.0, high 1.1.
- Room type factor: bedroom 1.0, living room 1.05, kitchen 1.15, office 1.0.
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Add extra load:
- Occupancy: +600 BTU/h for each person above two.
- Large windows: +1000 BTU/h per large glazed area.
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Overall BTU/h requirement:
BTU = Area(ft²) × 20 × height factor × climate factor × insulation factor × sun factor × room factor + occupancy load + window load - Convert to refrigeration tons: Tons = BTU / 12000.
- Convert to kilowatts (approximate): kW = BTU ÷ 3412.
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If efficiency and usage are provided:
- Electrical input power: kW_input = BTU / (EER × 1000).
- Monthly energy: kWh_month = kW_input × hours/day × days/month.
- Monthly cost: Cost = kWh_month × electricity rate.
This method is simplified and intended for initial selection. Detailed building load calculations may give different results for complex spaces.
How to use this calculator
- Measure the room length and width in metres, rounding sensibly.
- Enter the ceiling height, or keep the default for typical rooms.
- Select the room type that best matches how the space is used.
- Choose the climate, insulation level and sun exposure from the lists.
- Enter the typical number of people and count of large windows.
- Adjust the design temperature difference if you expect extreme heat.
- Optionally fill efficiency, hours, days and electricity cost fields.
- Click “Calculate cooling size” to see recommended sizing and capacity.
- Review the suggested tonnage, estimated energy use and running cost.
- Repeat for other rooms and use the CSV or PDF export to save results.
Always consult a qualified heating and cooling professional before making final installation decisions, especially for commercial or multi-room systems.
Typical cooling load per square metre
Many homes fall between eighty and one hundred forty watts of cooling per square metre, depending on climate, insulation, and glazing. This tool adjusts those rule-of-thumb values automatically using your specific dimensions, usage, and envelope characteristics.
Impact of ceiling height on air conditioner sizing
Higher ceilings increase room volume and the amount of air that must be cooled. The calculator scales cooling load using a height factor so tall rooms, lofts, and double-height spaces do not end up with undersized units.
How windows and solar gain change capacity
Large sun-exposed windows can significantly raise cooling requirements. Extra BTU allowances for each large glazed area, combined with the sun exposure selector, help you see the impact of different curtain choices, shading, and orientations on required unit size.
Comparing kitchen, bedroom and living room loads
Kitchens, with ovens and cooktops, usually need more cooling than bedrooms of the same size. Living rooms often host more people and electronics. Room-type factors inside the calculation reflect these different internal heat gains automatically.
Linking cooling design with lighting decisions
Lighting adds heat to a room, especially with older lamps. When planning comfort, pair this tool with the Basement Lighting Calculator and Cost to Install Recessed Lighting Calculator to balance brightness, cooling load, and electricity usage together.
Using running cost estimates for budgeting
By entering efficiency rating, hours of use, and local electricity prices, the calculator estimates monthly energy cost. This helps you compare smaller efficient units against larger, cheaper models when deciding which system matches your comfort and budget priorities.
When to commission professional load calculations
Detailed Manual J or similar calculations are recommended for new builds, major renovations, multi-room ducted systems, or properties with large glazing and shading differences. Use this tool for early planning, then ask HVAC designers to confirm capacities before installation.
Air conditioner room size calculator FAQs
How accurate is this air conditioner room size estimate?
Results are ballpark engineering estimates, not a replacement for detailed load calculations. They work well for typical homes and small offices. Complex layouts, very high ceilings, or unusual gains should always be checked by a qualified HVAC professional.
Can I use this calculator for multiple connected rooms?
Yes. Run separate calculations for each room or zone using its own dimensions, usage and exposure. Then total the recommended tonnage to size a multi-split or central system, adjusting slightly for doors kept open most of the time.
What if my room already has a window or portable unit?
You can still use this tool to estimate the total cooling requirement. Compare that load with your unit’s rating or our Window/Portable AC BTU by Room & Solar Gain Calculator, then decide whether supplemental or replacement cooling makes more sense.
Does choosing a higher efficiency rating always reduce my bill?
Higher EER or seasonal efficiency usually lowers energy use for the same cooling load, especially at long daily runtimes. However, very efficient units can cost more upfront, so compare purchase price, expected hours of use, and electricity rates together.
Which unit size should I pick if results sit between ratings?
Choose the closest standard size slightly above the calculated tonnage, particularly in hot climates or sunny rooms. Avoid oversizing by more than one rating step, because very large units may short cycle, reducing comfort, dehumidification and efficiency noticeably.