How many BTU do I need for a 12 x 12 room?

144 sq ft falls in the ENERGY STAR 100 to 150 sq ft row, so 5,000 BTU before any adjustments. Add 10% if it is very sunny and 600 BTU per person over two. With the hot-climate allowance for Dubai, that becomes about 6,250 BTU, or up to about 7,600 for a sunny room with three people, so a 9,000 BTU split is the usual pick.

How many square feet does 1 ton of AC cool?

One ton is 12,000 BTU. On the ENERGY STAR chart, 12,000 BTU covers 450 to 550 sq ft in a temperate climate. In the Gulf, with the 25% hot-climate allowance, a 1 ton unit suits roughly a 350 to 450 sq ft room with an 8 ft ceiling, and less if the room is sunny or the ceiling is higher.

How do I convert BTU to tons?

Divide by 12,000. 18,000 BTU is 1.5 tons and 24,000 BTU is 2 tons.

Does ceiling height matter?

Yes. The ENERGY STAR chart assumes 8 ft. A taller room has more air to cool. This calculator adds the same percentage as the extra height, so a 9 ft ceiling adds 12.5%.

Can I measure in meters?

Yes. Switch to meters and enter the room in meters. The calculator converts to square feet to read the chart. 1 sq m is 10.76 sq ft.

Is this accurate enough for a central AC system?

No. It is for sizing a window, portable, or single split unit for one room. A whole-home system needs a load calculation (Manual J in the US) from an HVAC contractor.

How many BTU is 1 kW?

About 3,412 BTU per hour. To go from BTU to kW, divide by 3,412. To go from kW to BTU, multiply by 3,412.

How many watts is 12,000 BTU?

About 3,517 watts, or 3.5 kW, of cooling capacity. The power the air conditioner actually draws is lower and depends on its efficiency rating.

What size mini split do I need for a 12 x 12 room?

On the ENERGY STAR chart a 144 sq ft room needs about 5,000 BTU, so the smallest common mini split, 9,000 BTU, is plenty in a temperate climate. Even with the 25% hot-climate allowance for the Gulf and a sunny room, it usually stays under 9,000.

How many BTU per square foot do I need for heating?

Roughly 30 to 60 BTU per hour per square foot as a rule of thumb: about 30 in mild climates, 40 moderate, 50 cold, and 60 very cold, adjusted for insulation and ceiling height. Treat it as an estimate.

How many BTU is a 1,500 watt space heater?

About 5,118 BTU per hour. Electric resistance heaters turn all the power they use into heat, so 1.5 kW x 3,412 = 5,118.

BTU Calculator: What Size Air Conditioner Do You Need?

Quick answer

Find the room’s square footage on the ENERGY STAR chart (a 150 to 250 sq ft room needs 6,000 BTU), then add 10% for a very sunny room, subtract 10% for a shady one, add 600 BTU per person over two, and add 4,000 BTU for a kitchen. One ton of cooling is 12,000 BTU per hour.

How many BTU do you need per square foot?

For small rooms it works out to more than you might expect: ENERGY STAR puts a 100 to 150 sq ft room at 5,000 BTU, which is 33 to 50 BTU per sq ft. As rooms get bigger the number per sq ft drops, to about 24 BTU per sq ft around 500 sq ft and under 20 above 1,000 sq ft. That is why this calculator reads the chart instead of multiplying by one fixed number.

The chart assumes an 8 ft ceiling. ENERGY STAR only says to consider more capacity for higher ceilings. This calculator scales the BTU up by the extra height (a 10 ft ceiling adds 25%), which is a common rule of thumb, not an official figure.

What adjustments does ENERGY STAR recommend?

Heavily shaded room: take off 10%. Very sunny room: add 10%. More than two people using the room regularly: add 600 BTU for each extra person. A unit used in a kitchen: add 4,000 BTU.

The calculator applies them in that order, after the ceiling adjustment, then rounds up to a common unit size (5,000, 6,000, 8,000, 9,000, 10,000, 12,000, 18,000, 24,000 BTU and so on).

How much bigger should an AC be in Dubai or the Gulf?

The ENERGY STAR chart is built for US conditions. Summers in the UAE regularly pass 45°C, and units run most of the day. HVAC suppliers in the region suggest about 20 to 30% more capacity than a temperate-climate calculation, and Daikin’s UAE guide uses 20 to 30 BTU per sq ft as a starting point that goes up for sunny walls and big windows.

The hot-climate box adds 25%, the middle of that range. Treat it as a planning number. A west-facing top-floor flat with single glazing may need more, and a shaded inner bedroom less. For a whole home or a central system, ask for a proper heat load calculation.

Worked example: a 14 x 12 ft bedroom

14 x 12 = 168 sq ft, which falls in the 150 to 250 sq ft row: 6,000 BTU. The room gets afternoon sun, so add 10%: 6,600. Three people use it regularly, one more than two: +600 = 7,200 BTU, about 0.6 tons. The nearest common size up is an 8,000 BTU window unit.

The same room in Dubai with a 9 ft ceiling: 6,000 + 12.5% for the ceiling = 6,750. +10% sun = 7,425. +600 for the third person = 8,025. +25% for the hot climate = about 10,031 BTU, so a 12,000 BTU (1 ton) split unit. That matches what most Dubai bedrooms of this size have fitted.

Why not just buy a bigger air conditioner?

ENERGY STAR warns that an oversized unit cools the air before it removes the humidity, so the room feels cold and clammy, and it costs more to buy and run. In a small apartment, a unit that is close to the right size and runs steadily is quieter and drier.

How many BTU do you need to heat a room?

A common rule of thumb is about 30 to 60 BTU per hour for each square foot, depending on how cold your winters are: roughly 30 in a mild climate, 40 in a moderate one, 50 where it snows regularly, and 60 in very cold regions. Take off about 15% for a well-insulated room and add about 25% for an old, drafty one.

Switch the calculator to Heating to run those numbers. For the same 14 x 12 ft bedroom in a moderate climate with average insulation: 168 sq ft x 40 = 6,720 BTU per hour, which is about 1.97 kW. These are estimates for sizing a room heater or checking a quote. A furnace or heat pump for a whole home should be sized with a Manual J load calculation.

What size mini split do you need?

Work out the cooling BTU for the room, then round up to the nearest standard mini split size: 9,000, 12,000, 18,000, 24,000, or 36,000 BTU. Pick Ductless mini split in the calculator and it does the rounding for you.

The 14 x 12 ft bedroom above needs about 7,200 BTU, so a 9,000 BTU head is the usual choice. The same room in Dubai comes to about 10,000 BTU, so a 12,000 BTU head. For several rooms on a multi-zone system, size each indoor head for its own room, and let the installer match the outdoor unit to the total.

How do you convert BTU to kW and watts?

Divide BTU per hour by 3,412 to get kilowatts, because the U.S. Energy Information Administration puts 1 kilowatt-hour at 3,412 BTU. Multiply kilowatts by 1,000 for watts. So a 12,000 BTU (1 ton) air conditioner has about 3.5 kW, or 3,517 watts, of cooling capacity.

That number is the heat the unit moves, not the electricity it uses. An air conditioner or heat pump draws much less power than its capacity in kW, and the efficiency rating on the label tells you how much. Plain electric heaters are the exception: they turn every watt into heat, so a 1,500 W heater gives about 5,118 BTU per hour.

What is the BTU formula?

Area (sq ft) = room length x room width (1 sq m = 10.76 sq ft)
Base BTU = ENERGY STAR chart value for that area (8 ft ceiling)
If the ceiling is over 8 ft: BTU x (ceiling height / 8)
Very sunny: +10%. Heavily shaded: -10%
+600 BTU for each regular occupant over 2
Kitchen: +4,000 BTU
Very hot climate (optional): +25%
Tons = BTU / 12,000
Kilowatts = BTU per hour / 3,412. Watts = kW x 1,000
Mini split: round up to 9,000, 12,000, 18,000, 24,000, or 36,000 BTU
Heating estimate: sq ft x 30 to 60 BTU (by winter climate), x ceiling / 8 if over 8 ft, -15% good insulation, +25% poor

Sources

The ceiling-height scaling and the 25% hot-climate allowance are rules of thumb used by HVAC installers, not part of the ENERGY STAR chart.

Frequently asked questions

How many BTU do I need for a 12 x 12 room?: 144 sq ft falls in the ENERGY STAR 100 to 150 sq ft row, so 5,000 BTU before any adjustments. Add 10% if it is very sunny and 600 BTU per person over two. With the hot-climate allowance for Dubai, that becomes about 6,250 BTU, or up to about 7,600 for a sunny room with three people, so a 9,000 BTU split is the usual pick.
How many square feet does 1 ton of AC cool?: One ton is 12,000 BTU. On the ENERGY STAR chart, 12,000 BTU covers 450 to 550 sq ft in a temperate climate. In the Gulf, with the 25% hot-climate allowance, a 1 ton unit suits roughly a 350 to 450 sq ft room with an 8 ft ceiling, and less if the room is sunny or the ceiling is higher.
How do I convert BTU to tons?: Divide by 12,000. 18,000 BTU is 1.5 tons and 24,000 BTU is 2 tons.
Does ceiling height matter?: Yes. The ENERGY STAR chart assumes 8 ft. A taller room has more air to cool. This calculator adds the same percentage as the extra height, so a 9 ft ceiling adds 12.5%.
Can I measure in meters?: Yes. Switch to meters and enter the room in meters. The calculator converts to square feet to read the chart. 1 sq m is 10.76 sq ft.
Is this accurate enough for a central AC system?: No. It is for sizing a window, portable, or single split unit for one room. A whole-home system needs a load calculation (Manual J in the US) from an HVAC contractor.
How many BTU is 1 kW?: About 3,412 BTU per hour. To go from BTU to kW, divide by 3,412. To go from kW to BTU, multiply by 3,412.
How many watts is 12,000 BTU?: About 3,517 watts, or 3.5 kW, of cooling capacity. The power the air conditioner actually draws is lower and depends on its efficiency rating.
What size mini split do I need for a 12 x 12 room?: On the ENERGY STAR chart a 144 sq ft room needs about 5,000 BTU, so the smallest common mini split, 9,000 BTU, is plenty in a temperate climate. Even with the 25% hot-climate allowance for the Gulf and a sunny room, it usually stays under 9,000.
How many BTU per square foot do I need for heating?: Roughly 30 to 60 BTU per hour per square foot as a rule of thumb: about 30 in mild climates, 40 moderate, 50 cold, and 60 very cold, adjusted for insulation and ceiling height. Treat it as an estimate.
How many BTU is a 1,500 watt space heater?: About 5,118 BTU per hour. Electric resistance heaters turn all the power they use into heat, so 1.5 kW x 3,412 = 5,118.

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