Free AC Tonnage Calculator
Not sure whether to buy a 1, 1.5 or 2 ton AC? Enter your room size and a few details about it, and this tool works out the cooling load and the AC size to buy, so you don't over-spend or end up with a room that never gets cold.
Floor area: 144 sq ft
Cooling load about 12,120 BTU/h (3.6 kW cooling)
- Room envelope
- 7,920 BTU
- People (2)
- 1,200 BTU
- Windows & doors (3)
- 3,000 BTU
- Sun & roof (average)
- ×1.00
- Total cooling load
- 12,120 BTU/h
A practical estimate for choosing an AC. For a large or unusual space, get a professional load survey before you buy.
Size your AC in four steps.
The calculator adds up every source of heat in the room, from the walls and ceiling to the people and the afternoon sun, then turns that total into the AC size you can actually buy.
Enter the room size
Type the length, width and ceiling height. Switch between feet and metres, whichever you measured in.
Add people and openings
Set how many people usually sit in the room, and how many windows and outside doors it has.
Set the conditions
Pick how much sun the room gets, whether it sits on the top floor, and how hot your climate runs.
Read the tonnage
You get the cooling load in BTU and the AC size to buy, rounded up to the nearest ton you can actually get.
How the tonnage maths works.
One ton of cooling removes 12,000 BTU of heat per hour. Work out the room's heat load in BTU, divide by 12,000, and round up to the nearest AC size.
The heat load
Add up where the heat comes from, then adjust for sun and roof.
Area = Length × Width
Envelope = Area × rate × (Height / 10)
People = Occupants × 600
Openings = Windows × 1,000 + Doors × 1,000
Load = (Envelope + People + Openings) × Sun × Roof
The per-square-foot rate rises with a hotter climate, and the sun and roof multipliers add up to a quarter more for a bright, top-floor room.
From BTU to tons
Convert the load into a size you can buy.
Tonnage = Load in BTU / 12,000
Round up to 0.75, 1, 1.5, 2, 2.5 or 3
Example: a 12 by 12 ft bedroom with a 10 ft ceiling, two people and a couple of windows in a hot climate comes to about 12,000 BTU, which rounds up to a 1.5 ton AC.
AC tonnage by room size.
A rough guide for a standard room with a normal number of people and moderate sun. A sunny, crowded or top-floor room needs the next size up, so use the calculator for your own room.
| AC size | Room area | Typically suits |
|---|---|---|
| 0.75 Ton | Up to 100 sq ft | Small cabins, study nooks and box rooms with one or two people. |
| 1 Ton | 100 to 140 sq ft | Small bedrooms and single-occupant offices with light sun. |
| 1.5 Ton | 140 to 200 sq ft | The typical master bedroom, the most common size for Indian homes. |
| 2 Ton | 200 to 300 sq ft | Living rooms, large bedrooms and small meeting rooms. |
| 2.5 to 3 Ton | 300 to 450 sq ft | Halls, open-plan spaces and shops. Bigger areas may need two units. |
Ranges are a starting point only. Ceiling height, insulation, window glazing and how the room is used all shift the real number.
What decides the tonnage.
Two rooms of the same size can need different ACs. These are the things that push the cooling load up or down.
Floor area times ceiling height sets the base load. A taller room holds more air to cool, so it needs more capacity.
Every person gives off body heat. A crowded living room or a shared office runs warmer than an empty one.
Glass lets heat in and doors to the outside leak cool air. More of them, or a west-facing wall, means a heavier load.
A sunny, west-facing room or a top floor with the roof baking above it can add a fifth or more to the cooling you need.
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Common AC tonnage questions.
It's a free tool that works out how much cooling a room needs and turns that into an AC size in tons. You enter the room dimensions, the number of people, windows and doors, and a few conditions like sun and climate. It adds up the heat load in BTU and divides by 12,000 to give you the tonnage to buy.
A ton is a unit of cooling, not weight. One ton of air conditioning removes 12,000 BTU of heat per hour, which is roughly 3.5 kilowatts of cooling. It comes from the amount of heat needed to melt one ton of ice in a day. So a 1.5 ton AC shifts about 18,000 BTU per hour.
Start with the floor area (length times width) and scale it for ceiling height to get the base load. Add about 600 BTU per person, 1,000 BTU per window and 1,000 BTU per outside door. Adjust up for a sunny or west-facing room, a top floor, or a hot climate. Divide the total BTU by 12,000 and round up to the nearest AC size. This calculator does all of that for you.
For a typical bedroom of about 140 to 200 square feet, a 1.5 ton AC is usually the right choice, which is why it is the most common size sold in India. A 1 ton unit suits a smaller room up to roughly 140 square feet with light sun and one or two people. Enter your actual room size above to see which side of the line you fall on.
A 1.5 ton AC comfortably cools a standard room of about 140 to 200 square feet with a normal ceiling. That range shrinks if the room is very sunny, sits on the top floor, holds a lot of people, or your summers are extreme, and it stretches a little for a shaded, lightly used room.
An undersized AC runs flat out and still never quite cools the room, which drives up your bill and wears the unit down. An oversized AC cools fast but switches off before it has pulled the humidity out, so the room feels cold and clammy and the compressor short-cycles. Getting the tonnage close to the real load is what keeps the room comfortable and the running cost sensible.
Yes. Most sizing rules assume a ceiling around 10 feet. A taller room holds more air to cool, so the load goes up roughly in proportion to the extra height. This calculator scales the base load by your ceiling height instead of assuming a fixed number, so a double-height room gets a fair estimate.
A top-floor room sits under a roof that soaks up sun all day and radiates heat down into it, and a west-facing room takes the full afternoon sun through its walls and windows. Both add to the heat the AC has to remove, often 10 to 25 percent more, so a room that would take a 1.5 ton unit on a shaded lower floor can need a 2 ton unit up top.
Tonnage is about cooling capacity, and both window and split ACs come in the same sizes, from 0.75 up to 2 tons and beyond. The tonnage you need is the same either way. Window versus split is a separate choice about fitting, noise and looks, so work out the tonnage first and then pick the type.
It gives a solid, practical estimate that lands on the right size for most homes and offices. It is not a full engineering load calculation, which would also weigh wall insulation, window glazing, orientation and local design temperatures. For a large space, an unusual building, or a commercial fit-out, get a professional Manual J or equivalent survey before you buy.
Yes on both. It's free, there's no sign-up, and it runs entirely in your browser. Nothing you type is sent anywhere or saved, so your numbers stay on your own device.
Disclaimer: This AC tonnage calculator gives a practical estimate to help you choose an air conditioner. It is not a full engineering load calculation and does not weigh every factor, such as wall insulation, window glazing, orientation or local design temperatures. For a large space, an unusual building or a commercial installation, have a qualified HVAC professional run a detailed load survey before you buy.
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