Home & Construction · Home Energy
AC Size Calculator — BTU & Tonnage
Find the right air-conditioner capacity for a room from its size, using the ENERGY STAR sizing chart, then adjust for a sunny or top-floor room, shade, extra people, a kitchen and a high ceiling. Shows BTU per hour, tonnage (1 ton = 12,000 BTU/h), kilowatts and the nearest standard AC size.
Your inputs
Quick start — try a typical case
The chart assumes 8 ft (2.4 m); higher ceilings need proportionally more.
Your result Live
Air Conditioner Size
7,500 BTU/h
0.63 ton · 2.2 kW for 168 sq ft
- Nearest Standard Size
- 0.75 ton (9,000 BTU/h)
- Room Area
- 168 sq ft · 15.6 m²
- ENERGY STAR Base (8 ft ceiling)
- 6,000 BTU/h
- Ceiling above 8 ft (×1.25)
- +1,500 BTU/h
Don't oversize: an AC that's too big cools the room quickly but switches off before removing humidity, leaving it cold and clammy — and wastes power.
Rooms with large west-facing windows, poor insulation or very hot summers may need one size up; a 5-star (BEE) inverter AC costs more upfront but much less to run.
How this is calculated
BTU/h = chart(area) × max(1, ceiling ÷ 8 ft) ± 10 % for sun/shade + 600 × (people − 2) + 4,000 if a kitchen · Tons = BTU/h ÷ 12,000
- chart
- ENERGY STAR capacity for the floor area (e.g. 150–250 sq ft → 6,000 BTU/h, 450–550 → 12,000)
- 1 ton
- 12,000 BTU/h ≈ 3.5 kW of cooling
Cooling capacity is measured in BTU per hour; in India ACs are sold by tonnage (1 ton = 12,000 BTU/h). The ENERGY STAR chart gives the capacity for a room's floor area with an 8-foot ceiling, and fixed adjustments account for sun, shade, people (each adds body heat) and kitchens (cooking heat). A taller room has more air to cool, so the base scales with ceiling height.
Assumptions & sources
- Room-sized cooling only; whole-house or commercial systems need a proper heat-load calculation.
- Ceiling-height scaling is linear above 8 ft.
- 1Room air conditioners — sizing chart and adjustments — ENERGY STAR (US EPA)
- 2Star labelling programme for room air conditioners — Bureau of Energy Efficiency, India
Calculator ID HOME-AC-001 · version 1.0.0
Common questions
How many tons of AC do I need for a 150 sq ft room?
About 6,000 BTU/h on the chart — a 0.75-ton AC for a normal room, or 1 ton if it's sunny, on the top floor or has a high ceiling.
What does 1 ton mean for an AC?
It's the cooling power to melt one ton of ice in 24 hours — 12,000 BTU per hour, or about 3.5 kW of cooling. It's not the weight of the unit.
Is a bigger AC better?
No. An oversized AC short-cycles: it cools fast but doesn't dehumidify, so the room feels clammy, and it uses more power.