Estimate AC capacity in BTU, tons and kW for a room.
Air Conditioner Size Calculator: Free Online Tool
The air conditioner size calculator gives a quick estimate of the cooling capacity needed for a single room. You enter the floor area, the ceiling height, the number of people and whether the room is shaded, normal or sunny, and whether it is a kitchen. The result is shown in BTU per hour, tons and kilowatts, followed by a suggested standard AC size.
Homeowners, interior contractors, site engineers and shop owners use this type of estimate before buying a split or window unit. A unit that is too small runs all day and never cools the room, while an oversized unit switches on and off frequently, wastes electricity and removes less moisture from humid air. The estimate is especially useful in hot and humid South Asian climates where the AC often runs for many hours.
When to use this calculator
Use it when you are choosing an AC for a bedroom, office, shop or small meeting room, or when you check a dealer's recommendation. It helps compare the same room with different numbers of occupants, with and without direct afternoon sun, or as a kitchen. It is a first estimate; for large halls, server rooms and central systems you should ask for a proper load calculation. It also gives a quick check on quotations and site requests before work starts. Shop owners and tenants also use it to judge whether one large unit or two smaller units will suit a long room.
How to use the Air Conditioner Size Calculator
- Open the calculator above on your phone, tablet or computer. Nothing needs to be installed and no sign-up is required.
- Choose the unit system first (feet / inches or metres / mm). The input labels change to match your choice.
- Pick the option you need from the drop-down list (Normal; Shaded; Sunny).
- Pick the option you need from the drop-down list (No; Yes).
- Enter your values in the input boxes: Room area (sq ft), Ceiling height (ft), Number of people, Sun exposure, Is it a kitchen?. The boxes already hold sample values, so overwrite them with your own.
- Press Calculate. The result appears straight away under the button.
- Change any value and press Calculate again to compare options. Press Reset to go back to the sample values.
- Check the result against your drawings, project specification and local code before you order material or approve work.
How the calculation works
The calculator converts the area to square feet and starts with a base load of 20 BTU per square foot. For ceilings higher than 8 ft, the base load is multiplied by height divided by 8. The load is then multiplied by 0.9 for a shaded room, 1.0 for normal and 1.1 for a sunny room. It adds 600 BTU for each person beyond two and 4000 BTU for a kitchen. Tons equal BTU per hour divided by 12,000, and kW is BTU/h x 0.000293. The suggestion is the next size from 0.75, 1, 1.5, 2, 2.5, 3, 4 and 5 tons.
Worked example
When you open the page the calculator is filled with sample values. Pressing Calculate with those values gives the result below, which you can use to check that you are reading the output correctly.
| Cooling load | |
|---|---|
| Room area | 200 sq ft |
| Base load (20 BTU per sq ft) | 4,000 BTU/h |
| Total cooling load | 5,000 BTU/h |
| Capacity in tons | 0.42 ton |
| Capacity in kW | 1.47 kW |
| Suggested AC size | 0.75 ton |
Tips and common mistakes
- Use the actual floor area of the room being cooled, and count connected rooms or open doors as part of the area.
- Select the sun exposure honestly; a top-floor room with a west wall or an uninsulated roof is usually sunny, not normal.
- Enter the number of regular occupants, since the calculator only adds load for people beyond two at 600 BTU each.
- Treat the suggested size as a starting point and round up to the nearest available model, not down.
- Remember that insulation, window size, glass type and appliances are not included, so get an engineer's load calculation for important or large spaces.
Frequently asked questions
What is the default room in the calculator?
The default is a 200 sq ft room with a 10 ft ceiling and two people in normal sun and not a kitchen. The base load is 4,000 BTU/h and the total is 5,000 BTU/h, about 0.42 ton, so the suggested size is 0.75 ton.
How many BTU are in one ton of AC?
The calculator uses 1 ton = 12,000 BTU per hour. The total cooling load is divided by 12,000 to give the capacity in tons, and it is also converted to kilowatts for comparison with equipment data.
Why does the ceiling height change the answer?
A higher ceiling means a larger volume of air to cool. For ceilings above 8 ft, the base load is multiplied by height divided by 8, so a 10 ft room gets a factor of 1.25. Lower ceilings are not reduced.
Is a kitchen treated differently?
Yes. Selecting kitchen adds 4,000 BTU per hour to the load to allow for heat from cooking and appliances. This can raise the suggested AC size by one step, so choose it only when the kitchen is part of the cooled space.
Is this estimate accurate enough for buying an AC?
It is a rule-of-thumb estimate and is acceptable for ordinary rooms. A load calculation by an engineer is more accurate, especially for large, glazed or heavily occupied spaces where the rule can be off.
Important note
This tool gives estimates for planning, study and quick checks. It does not replace design by a qualified engineer, site-specific testing, or the requirements of your project specification and local building code. Always confirm final quantities, test results and acceptance limits with the responsible engineer before using them for construction or payment.
