How many tons of AC do I need?

Divide the BTU your room needs by 12,000. A room needing 18,000 BTU needs 1.5 tons. Put your figures in above and it also tells you which standard size to buy.

How many BTU is 1.5 ton?

18,000 BTU per hour. One ton is 12,000, so 1.5 tons is one and a half times that.

What size AC for a 20 square metre room in Dubai?

Around 12,000 BTU on a middle floor, so a 1 ton unit, though many people fit 1.5 tons for comfort. On a top floor or with a lot of glass, 1.5 tons is the safer choice.

Should I round up or down on tonnage?

Round up if you are more than about ten per cent over a size. If you are only just over, stay with the smaller one. It will run longer, which dehumidifies better and costs less to run.

Is one ton of AC enough for a bedroom?

For a small bedroom up to about 14 square metres on a middle floor, usually yes. For a master bedroom, or anything on a top floor, 1.5 tons is more realistic here.

Does tonnage tell me the running cost?

No. Two units of the same tonnage can use quite different amounts of power. Look at the efficiency rating and whether it is an inverter, then use the running cost calculator.

AC Tonnage Calculator

What do you know

BTU needed

BTU

Use this if you picked BTU above.

Room floor area

Use this if you picked room size above.

BTU per square metre

Safety margin

Only add a margin if you know the room is hard to cool.

Your answer

Size to buy

1.5 ton

Your room works out at 1.5 tons, so 1.5 ton is the size above it.

Cooling needed: 18000 BTU
Exact tonnage: 1.5 tons
Next size down: 1.5 ton
In kilowatts: 5.3 kW

Standard sizes in the UAE are 1, 1.5, 2, 2.5, 3, 4 and 5 tons. Anything between those means choosing one of the two either side.

AC Tonnage Calculator for Dubai and the UAE

This tool turns a cooling figure into tons, and then tells you which size of unit to actually buy.

Air conditioners are not sold in every size. They come in steps: 1 ton, 1.5, 2, 2.5, 3 and so on. Your room might need 1.7 tons, but nobody sells that.

So the useful answer is not the exact number. It is which of the sizes on the shelf is the right one, and this tells you that.

Tons, BTU and what the shop means

A ton of cooling has nothing to do with weight. It comes from an old measure: how much heat it takes to melt a ton of ice in a day.

In numbers, one ton is 12,000 BTU per hour. That is the whole conversion, and everything else follows from it.

So a 1.5 ton split is an 18,000 BTU unit. A 2 ton is 24,000. A 2.5 ton is 30,000. If a shop quotes you one and the box says the other, they are the same thing.

Some brands print the number as kW instead. One ton is about 3.5 kW of cooling. A 3.5 kW unit and a 1 ton unit are the same machine.

Which way to round

This is the real question, because your room almost never lands exactly on a size that exists.

The default is to round up. If the room needs 1.7 tons, take 2 tons. A slightly oversized unit will short cycle a little, but an undersized one will run at full power all day and still not reach the set temperature, and that is worse in every way.

The exception is when you are only just over. If a room needs 1.55 tons, taking 2 tons is a big jump. A 1.5 ton unit that runs almost continuously in August is doing exactly what it should, and it will dehumidify better than a 2 ton unit that keeps switching off.

The rule that works: round up if you are more than about ten per cent over a size. Stay put if you are just under it.

If you cannot decide, this is a good moment to have somebody look at the room rather than guess between two sizes.

Rough sizes for UAE rooms

A sense check for the answer above. Every one of these can be wrong for a particular room.

Small bedroom, up to 14 m2
Usually 1 ton. On a top floor or with a west facing window, 1.5.
Master bedroom, 15 to 22 m2
Usually 1.5 tons. Two people sleeping in it and an ensuite door open makes 2 tons worth considering.
Living room, 25 to 35 m2
Usually 2 to 2.5 tons. A lot depends on how much glass there is and which way it faces.
Open plan living and kitchen
Treat it as one space, and remember the kitchen adds heat. Often 3 tons or more, sometimes two units.
Double height majlis
Needs a real calculation. The floor area misleads badly here, because the volume is double.
Small shop or office
Depends on people, lighting and equipment far more than on floor area. Get it surveyed.

Split, window or ducted

Tonnage tells you the size. It does not tell you the type. That is a separate decision.

Split unit
The most common in UAE flats and villas. One indoor unit per room, outdoor unit on a balcony or roof. Quiet inside and easy to replace one room at a time.
Window unit
One box in the wall or window. Cheap and simple, noisier, and now mostly found in older buildings and staff accommodation.
Ducted
One larger unit feeding several rooms through ducts in the ceiling. Tidy and quiet, but a fault affects the whole floor and duct cleaning becomes part of the maintenance.
Central or chilled water
Common in towers. You do not choose the tonnage, the building does. What you control is the fan coil and the thermostat.

What tonnage does not tell you

Two units of the same tonnage can behave very differently, and the difference is not printed as large on the box.

The first is efficiency. Two 1.5 ton units can use noticeably different amounts of electricity for the same cooling. That is the EER or the star rating, and over a Dubai summer it shows up on the bill.

The second is inverter or fixed speed. A fixed speed unit is either on at full power or off. An inverter unit slows down instead of stopping, so it holds a steadier temperature, dehumidifies better and uses less power at part load. In a climate where the AC runs most of the year, that matters.

The third is the installation. A perfectly sized unit fitted with pipe runs that are too long, poorly insulated, or charged with the wrong amount of gas will never give you its rated cooling.

So use the tonnage to shop with, then ask about the efficiency and about who is fitting it.

Questions people ask

How many tons of AC do I need?: Divide the BTU your room needs by 12,000. A room needing 18,000 BTU needs 1.5 tons. Put your figures in above and it also tells you which standard size to buy.
How many BTU is 1.5 ton?: 18,000 BTU per hour. One ton is 12,000, so 1.5 tons is one and a half times that.
What size AC for a 20 square metre room in Dubai?: Around 12,000 BTU on a middle floor, so a 1 ton unit, though many people fit 1.5 tons for comfort. On a top floor or with a lot of glass, 1.5 tons is the safer choice.
Should I round up or down on tonnage?: Round up if you are more than about ten per cent over a size. If you are only just over, stay with the smaller one. It will run longer, which dehumidifies better and costs less to run.
Is one ton of AC enough for a bedroom?: For a small bedroom up to about 14 square metres on a middle floor, usually yes. For a master bedroom, or anything on a top floor, 1.5 tons is more realistic here.
Does tonnage tell me the running cost?: No. Two units of the same tonnage can use quite different amounts of power. Look at the efficiency rating and whether it is an inverter, then use the running cost calculator.

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