How to use this calculator
- 1Measure the room's length and width in feet or metres, or enter its floor area.
- 2Enter the ceiling height. The makers' charts assume 10 ft (3 m); a higher ceiling raises the size.
- 3Keep "Very hot, 40–50 °C" for Pakistan, North India and the Gulf, and tick "Top floor" if the room is right under a roof the sun beats on.
- 4Choose how sunny the room is, how many people normally use it and whether it is a kitchen.
- 5Read the size in tons and pick that size — or the next one up — when you buy. Compare the cooling capacity on the label (BTU/h or kW) too.
The formula
- 01Cooling needed = floor area in ft² × 95 BTU/h (about 300 W per m²)
- 02× your ceiling height ÷ 10 ft, only if the ceiling is higher
- 03× 1.1 if very sunny, × 0.9 if shaded · × 1.25 on a top floor under a sun-baked roof
- 04+ 600 BTU/h for each regular occupant beyond two · + 4,000 BTU/h for a kitchen
- 05Tons = BTU/h ÷ 12,000 → size to buy = the next size on sale (0.75, 1, 1.5, 2, 2.5, 3, 4 ton)
AC makers in South Asia size split units from room-size charts for 45–50 °C summers: Voltas gives 1 ton for 91–130 ft², 1.5 ton for 131–190 ft² and 2 ton for 191–250 ft² with a 10 ft ceiling and two people. That is about 95 BTU/h per ft² — 1 ton for every 126 ft² — which is the figure used here.
A room right under a flat concrete roof in full sun gains much more heat than one below another floor, so the calculator adds 25 %; sunny or shaded rooms get ±10 %, and each extra person and a kitchen add a fixed amount, as in the ENERGY STAR method.
A "ton" is a size class, not an exact rating: 1 ton of cooling is 12,000 BTU/h (3.5 kW), and many 1.5-ton inverter units are rated nearer 5 kW (17,000 BTU/h). Check the rated cooling capacity on the label or data sheet against the figure here.
Worked example
A 15 ft × 12 ft room with a 10 ft ceiling is 180 ft².
In 40–50 °C summers that needs about 17,100 BTU/h — 1.43 tons (AC) — so the size to buy is 1.5 tons (AC). On a top floor under the roof it would need 25 % more.
Tips before you buy
- Buy a unit rated for high outdoor temperatures (often labelled T3) and keep its outdoor part in the shade with room for air to flow.
- An inverter AC runs more efficiently when it is close to the right size; a much bigger unit costs more and removes less humidity.
- Insulate or shade a sun-baked roof (roof insulation, white roof coating) — it can cut the size a top-floor room needs.
- Close curtains on west-facing windows in the afternoon; sun through glass is a large part of the heat.
- If a wide opening joins another room or a corridor, include that area too.
Frequently asked questions
Which AC ton is right for my room size?
In 40–50 °C summers, with a 10 ft ceiling: up to about 120–130 ft² → 1 ton, up to about 190 ft² → 1.5 ton, up to about 250 ft² → 2 ton (Voltas and Haier India charts). A room under a sun-baked roof needs about 25 % more.
Is a 1.5 ton AC enough for a 12 × 14 ft room?
12 × 14 ft is 168 ft². At 95 BTU/h per ft² that is about 16,000 BTU/h, or 1.33 ton, so a 1.5 ton unit fits with a 10 ft ceiling. On a top floor under the roof it becomes about 1.66 ton — choose 2 ton.
How many BTU is 1 ton of AC?
12,000 BTU per hour, about 3.5 kW of cooling. 1.5 ton is 18,000 BTU/h (5.3 kW) and 2 ton is 24,000 BTU/h (7 kW).
Should I buy a bigger AC to be safe?
Only a little bigger. An oversized unit cools in short bursts, removes less humidity and wastes energy. Choose the size shown, or the next one up if the room is very sunny or under the roof.
Does a higher ceiling need a bigger AC?
Yes. The charts assume a 10 ft ceiling; a 12 ft ceiling holds 20 % more air and has more wall to heat up, so the calculator adds 20 %. This proportional adjustment is our estimate.
Also searched as: AC tonnage calculatorhow many ton AC for my roomAC size calculator PakistanAC ton calculator India1.5 ton AC for what room sizesplit AC size calculatorroom size for 1 ton AC
Sources
- ENERGY STAR – Room air conditioners: sizing chart and adjustments (sun, people, kitchen, 8 ft ceiling)
- CHOICE – What size air conditioner do I need? (AIRAH cooling calculator: 30 m² room, Perth 3.0 kW, Sydney 2.3 kW; 2.9 kW with no roof insulation)
- Voltas – AC room size chart (≤ 90 ft² 0.75 ton, 91–130 ft² 1 ton, 131–190 ft² 1.5 ton, 191–250 ft² 2 ton; 10 ft ceiling, 2 people)
- Haier India – How to calculate AC tonnage for your room (up to 120 ft² 1 ton, 120–180 ft² 1.5 ton)
- Daikin Australia – split system range (2.0, 2.5, 3.5, 5.0, 6.0, 7.1 kW …)
- ACCA – Manual J, the ANSI-recognised standard for residential heating and cooling load calculations
- NIST SP 811, Appendix B.8 – 1 BTU(IT)/h = 0.2930711 W; 1 ton of refrigeration = 3,516.853 W
Formulas last reviewed: September 30, 2026 ·How we check our formulas