AC Tonnage & BTU Calculator: Room Cooling Load

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Formula at a glance

AC Tonnage & BTU Calculator: Base load — Floor area (sq ft) × 70 BTU × climate factor × (height ÷ 10 ft). Example: 14 × 12 ft bedroom, hot city → Recommended AC: 1.5 ton — How the AC Tonnage & BTU Calculator works: Base load — Floor area (sq ft) × 70 BTU × climate factor × (height ÷ 10 ft)

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📘 About the AC Tonnage and BTU Calculator

Air conditioners are rated in tons of cooling: 1 ton removes 12,000 BTU of heat per hour (3.517 kW). The heat in a room comes from the walls and roof, sunlight through windows, people (about 600 BTU each) and appliances.

This calculator starts with about 70 BTU per square foot — matched to Indian AC sizing guides (about 1 ton for 120–140 sq ft in a hot city), because concrete homes with little insulation gain far more heat than well-insulated homes — adjusts for ceiling height and climate, then adds heat for a top floor, strong sun, extra people, cooking, appliances and windows. It shows the full breakdown, the exact tonnage and the nearest standard AC size.

🧮 Formula

Base load

Floor area (sq ft) × 70 BTU × climate factor × (height ÷ 10 ft)

Tons

Total BTU per hour ÷ 12,000

kW of cooling

BTU per hour ÷ 3,412

✏️ Worked examples

14 × 12 ft bedroom, hot city

You enter
Measure in	feet
Room length	14
Room width	12
Ceiling height	10
Summer climate	Hot (35–40 °C)
Floor	Ground / middle floor
Sunlight	Normal
People usually in the room	2
Kitchen or cooking in the room?	No
Heat from appliances & lights	300 W
Number of windows	2

You get
Recommended AC	1.5 ton
Cooling load	12,784 BTU per hour
Exact tonnage	1.07 ton
In kilowatts of cooling	3.75 kW
Floor area	168 sq ft (15.6 m²)

1.5 ton (12,784 BTU per hour).

Top-floor 18 × 15 ft living room, very hot

You enter
Measure in	feet
Room length	18
Room width	15
Ceiling height	10
Summer climate	Very hot (above 40 °C — Delhi, Rajasthan, UP)
Floor	Top floor (roof above)
Sunlight	Very sunny / west-facing
People usually in the room	4
Kitchen or cooking in the room?	No
Heat from appliances & lights	500 W
Number of windows	3

You get
Recommended AC	3 ton
Cooling load	33,248 BTU per hour
Exact tonnage	2.77 ton
In kilowatts of cooling	9.74 kW
Floor area	270 sq ft (25.1 m²)

3 ton.

🧭 How to use this calculator

What you enter

Measure in
Room length
Room width
Or floor area (optional)sq ft or m² — instead of length × width.
Ceiling height
Summer climate
Floor
Sunlight
People usually in the room
Kitchen or cooking in the room?
Heat from appliances & lights (W)
Number of windows

What you get

Recommended AC
Cooling load
Exact tonnage
In kilowatts of cooling
Floor area

💡 BTU to ton quick table

9,000 BTU = 0.75 ton
12,000 BTU = 1 ton
18,000 BTU = 1.5 ton
24,000 BTU = 2 ton
30,000 BTU = 2.5 ton

❓ Frequently asked questions

How many BTU is a 1.5-ton AC?

18,000 BTU per hour (1.5 × 12,000), or about 5.3 kW of cooling.

What size AC do I need for a 150 sq ft room?

Usually 1–1.5 tons; choose 1.5 tons for a top floor, a very hot city or a sunny west-facing room.

Is a bigger AC better?

Slightly oversizing an inverter AC is fine; a much larger non-inverter AC cools in short bursts and leaves the room humid.

❄️ AC Tonnage and BTU Calculator: Cooling Load of a Room