Tons, BTU per hour and kilowatts are three ways of writing one rate of heat removal. What none of them is, is the electricity the machine uses.
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1.5 ton
5.275 kW of cooling
A rate of heat removal, not an energy and not a mass. One ton is the rate that melts a short ton of ice in a day — 3,516.85 W.
The same capacity in every unit
Cooling-capacity units, converted from your figure
Unit
Value
What it is
watt
5,275.3
The SI unit of heat flow. What a European specification uses.
kilowatt
5.275
The working unit for cooling across Europe and Australia.
BTU per hour
18,000
The US working unit, usually written just “BTU” on a box — always a rate, never an energy.
ton of refrigeration
1.500
The rate that melts a short ton of ice in a day. Standard in the US and universal in India.
kilocalorie per hour
4,535.9
Still met on older equipment and in parts of Asia.
frigorie per hour
4,535.9
A kilocalorie per hour under a different name — the same rate, counted as cooling.
A box marked “12,000 BTU” means 12,000 BTU per hour. A BTU is a quantity of heat and a capacity has to be a rate, so the missing “per hour” is not shorthand for something else — it is the difference between a quantity and a rate. There are two BTU definitions in circulation, and they differ by 0.067%, far below the tolerance on any capacity rating; this uses the International Table one.
Cooling capacity is not electricity used
Heat removed5.28 kWwhat the unit is rated at
Electricity drawn1.32 kWa 4.0× difference — EER 13.6
Running current at 230 V6.0 Asizing on the capacity instead would say 24.1 A
The same 5.28 kW of cooling, at different efficiencies
COP
EER
Electricity drawn
2.5
8.5
2.11 kW
3.0
10.2
1.76 kW
3.5
11.9
1.51 kW
4.0
13.6
1.32 kW
4.5
15.4
1.17 kW
5.0
17.1
1.06 kW
5.5
18.8
0.96 kW
An air conditioner moves heat rather than making it, which is why it can remove several times more heat than the electricity it consumes. A 1.5-ton unit removes 5.28 kW while drawing about 1.3 kW. Sizing a circuit or a generator on the cooling figure over-specifies it by three to five times.
Which efficiency figures are comparable
As a COP3.517exact — EER and COP differ only by units
Efficiency ratings, and whether they convert
Rating
Where
Converts to COP?
What it measures
COP — coefficient of performance
International
Exactly
Watts of cooling per watt drawn, at one rating point. Dimensionless.
EER — energy efficiency ratio
United States
Exactly
BTU/h of cooling per watt drawn, at one rating point. The same measurement as COP in different units.
SEER / SEER2
United States
No
Weighted across a US cooling season. Not a single operating point, and SEER2 uses different test pressures from SEER.
ISEER
India
No
Weighted across the Indian temperature bin distribution defined by BEE. Different profile, so not comparable with SEER.
SEER (EU) / ESEER
European Union
No
Weighted across a European profile under EN 14825. Different again.
SCOP
European Union
No
The heating-season counterpart of SEER, over a defined climate.
EER and COP are the same measurement in different units, so they convert with no assumption: EER = COP × 3.412. The seasonal figures do not. SEER, ISEER and the European SEER each average performance over a different national temperature distribution, so a US SEER 18 and an Indian ISEER 5 describe machines tested against different weather, and there is no factor between them.
The sizes actually sold
Standard unit capacities in all three conventions
Size
BTU/h
kW
Typically
0.75 ton
9,000
2.64
A small bedroom or a cabin.
1 ton
12,000
3.52
A standard bedroom.
1.5 ton
18,000
5.28
The commonest domestic size in India.
2 ton
24,000
7.03
A large room or a small open-plan space.
2.5 ton
30,000
8.79
3 ton
36,000
10.55
A small whole-home system in the US.
5 ton
60,000
17.58
The usual upper limit for a residential system.
The reason the BTU figures are round thousands and the kilowatt figures are not is that the ton was defined in BTU. India and the United States size in tons, Europe and Australia in kilowatts, and the same machine carries different-looking numbers in each market. Capacity is only one part of choosing a unit — room volume, glazing, orientation, occupancy and insulation all matter, and an oversized unit cools quickly and dehumidifies badly.
What this converter covers
Convert between every capacity unit, then see what the unit actually draws from the wall — and which efficiency ratings can be compared at all.
Tons of refrigeration, BTU/h, watts, kilowatts and kcal/h
Electricity drawn and running current at a stated COP
EER and COP, which convert exactly
SEER, ISEER and SCOP, which do not — and why
The standard unit sizes in all three market conventions
A rate, not a mass Capacity ≠ consumption Seasonal ratings differ India, US, EU
Free, no signup — exact by definition, not an estimate.
Updated 8 September 2026
At a glance
Formula shown
1 ton = 12,000 BTU/h = 3516.85 W · power drawn = capacity ÷ COP · EER = COP × 3.412
Scenario support
1.5 ton is 18,000 BTU/h and 5.28 kW · at COP 4 it draws 1.32 kW, about 6 A at 230 V
Educational estimate
Planning support from the values you enter — not professional advice.
A ton is a rate, not a weight
A “1.5 ton” air conditioner does not weigh a ton and a half, and the number has nothing to do with how heavy it is. A ton of refrigeration is a rate of heat removal: the rate at which a short ton of ice melts over twenty-four hours.
The arithmetic is worth seeing once, because it explains the otherwise arbitrary 12,000. The latent heat of fusion of ice is about 144 BTU per pound. Two thousand pounds of it is 288,000 BTU. Spread over twenty-four hours that is 12,000 BTU per hour — and in SI, 3516.85 W.
The sizes sold, in all three conventions
Tons
BTU/h
kW
0.75
9,000
2.64
1
12,000
3.52
1.5
18,000
5.28
2
24,000
7.03
3
36,000
10.55
5
60,000
17.58
The unit survives because ice was how cooling was sold before machines did it. A plant that could replace the ice a customer used to buy was described by the tonnage it displaced, and the name outlived the trade entirely.
It also explains why the BTU column is round and the kilowatt column is not. The ton was defined in BTU, so the metric figures inherit an awkward factor. A European specification for the same machine would simply say 5.3 kW.
“12,000 BTU” is missing two words
Every air conditioner sold in North America and much of Asia is advertised with a BTU figure, and the figure is always a rate with the “per hour” dropped. A BTU is a quantity of heat, like a joule. A capacity has to be a rate, like a watt.
Most of the time the abbreviation is harmless, because nobody is offering to remove 12,000 BTU total. It stops being harmless the moment a BTU figure is compared with an energy figure — a gas bill in therms, a battery in kilowatt hours, a heater rated in kilowatts.
The test is dimensional. If a number describes how fast something happens, it needs a time in its units: BTU/h, watts, kW. If it describes how much, it does not: BTU, joules, kWh. An air conditioner’s capacity is a speed; its running cost is a quantity. Mixing them silently is the commonest arithmetic error in this area.
One small footnote, because it comes up: there are two BTU definitions in circulation. The International Table BTU is 1055.05585262 J and the thermochemical one is 1054.35 J. They differ by 0.067%, which is far below the tolerance on any capacity rating — a couple of watts on a five-kilowatt unit. This page uses the International Table value.
Cooling capacity is not electricity
A 1.5-ton unit removes 5.28 kW of heat from a room. It does not consume 5.28 kW of electricity — it consumes something closer to 1.3. The difference is not a rounding: it is the entire reason a heat pump is worth having.
An electric heater turns a kilowatt of electricity into a kilowatt of heat, and cannot do better. An air conditioner moves heat from inside to outside, and moving is cheaper than making. The ratio is the coefficient of performance, and it is typically 3 to 5.
A 1.5 ton unit, at different efficiencies
COP
EER
Electricity drawn
Current at 230 V
2.5
8.5
2.11 kW
9.7 A
3.0
10.2
1.76 kW
8.0 A
4.0
13.6
1.32 kW
6.0 A
5.0
17.1
1.06 kW
4.8 A
The practical consequence is about sizing everything downstream. A circuit, a generator, a solar system or an inverter has to carry the consumption, not the capacity — and using the capacity figure over-specifies it by three to five times. It is an expensive mistake in the direction that looks cautious.
Two honest caveats. Efficiency is quoted at one test condition and falls as the outdoor temperature rises, so a unit rated COP 4 will be doing worse than that on the day it is working hardest. And these are running figures: a fixed-speed compressor draws several times its running current for a moment at start-up, which is what a breaker has to tolerate without tripping, even though it does not affect the energy bill.
Which efficiency numbers compare
There are two kinds of efficiency rating and they behave completely differently. One kind converts exactly; the other cannot be converted at all.
COP and EER are one measurement in two units. COP is watts of cooling per watt drawn; EER is BTU/h of cooling per watt drawn. They differ only by the BTU-to-watt-hour factor, so EER = COP × 3.412 exactly, with nothing assumed. Both are measured at a single specified operating point.
Everything seasonal is an average over a national climate. SEER, ISEER, the European SEER and SCOP each weight performance across a temperature distribution defined by a jurisdiction. They are not rating points, and there is no factor that converts one into another or into a COP.
What each rating is, and whether it travels
Rating
Where
Comparable across borders?
COP
International
Yes — a rating point
EER
United States
Yes — the same point, other units
SEER / SEER2
United States
No — US season
ISEER
India
No — Indian temperature bins
SEER (EU)
European Union
No — EN 14825 profile
SCOP
European Union
No — heating season
So the calculator converts EER and COP and refuses to convert the seasonal figures. That refusal is the useful part: an Indian ISEER of 5 and a US SEER of 18 are not two readings of one thing, and putting them side by side to pick a machine compares performance against two different climates.
Within one market the seasonal figures are exactly what to compare, because that is what they are for — they capture part-load behaviour that a single rating point misses entirely, which is where an inverter-driven unit earns its advantage. The mistake is only in carrying them across a border.
Three markets, three conventions
The same machine is described three ways depending on where it is sold, which is why a specification sheet often carries all three.
India sizes domestic air conditioning in tons almost universally — 1 ton, 1.5 ton, 2 ton — and rates efficiency in ISEER stars. The ton is so entrenched that room-size guidance is written in it, and the BTU figure rarely appears in retail at all.
The United States uses tons for whole-home systems and BTU/h for room units, and rates in SEER2 and EER2. A 3-ton system and a 36,000 BTU/h system are the same thing described for two different audiences.
Europe and Australia use kilowatts throughout and rate in SEER and SCOP under the EN standards. A 5.3 kW unit is what everyone else calls 1.5 ton, and the ton is essentially unknown.
None of this changes the machine. It does mean that comparing a shortlist assembled from different markets requires converting the capacity — which is arithmetic — and being careful about the efficiency figures, which is not. Capacity travels; seasonal efficiency does not.
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The ton of refrigeration is an ASHRAE definition with a physical origin — the heat absorbed by a short ton of ice melting over a day — which is why it comes out at the oddly specific 3516.85 W rather than a round number. The two BTU definitions are both listed by NIST, and the difference between them is under a tenth of a per cent. ISEER is defined by India’s Bureau of Energy Efficiency over an Indian temperature distribution, which is the concrete reason it cannot be compared with a US SEER.
ASHRAE TerminologyAmerican Society of Heating, Refrigerating and Air-Conditioning Engineers · verified 2026-09-08 · The ton of refrigeration as 12,000 BTU/h, defined from the latent heat of fusion of a short ton of ice melted over twenty-four hours, and the definitions of coefficient of performance and energy efficiency ratio
NIST Special Publication 811 — Guide for the Use of the International System of UnitsNational Institute of Standards and Technology · verified 2026-09-08 · The International Table BTU as exactly 1055.055 852 62 J and the thermochemical BTU as 1054.35 J — the two definitions in circulation, and the basis for the exact ton-to-watt figure used here
BEE Star Labelling Programme for Room Air ConditionersBureau of Energy Efficiency, Government of India · verified 2026-09-08 · ISEER as a seasonal figure weighted over the Indian temperature bin distribution, which is why it is not comparable with the US SEER or the European seasonal figures despite all three being seasonal ratios
Conversion note
This converts capacity units and shows the relationship between capacity, efficiency and electrical demand. It does not size an air conditioner. A real load calculation accounts for floor area and ceiling height, glazing area and orientation, insulation levels, air infiltration, occupancy, lighting and appliance gains, and the local design temperature — and a unit sized by any rule of thumb is as likely to be too big as too small. Oversizing is a real fault rather than a safe margin: a unit that reaches temperature too quickly short-cycles and removes far less humidity, which leaves a room cold and clammy. The COP and efficiency figures here are whatever you enter; a real unit's performance falls as the outdoor temperature rises, and a nameplate rating is measured at one specified condition. Electrical figures are the running load only and ignore starting current, which for a fixed-speed compressor can be several times higher and is what a protective device must tolerate. For an installation, use a proper load calculation and the manufacturer's performance data.
Published the Tons to BTU Converter: air-conditioning capacity in tons of refrigeration, BTU per hour, watts, kilowatts and kilocalories per hour.
Establishes that a ton of air conditioning is a RATE of heat removal rather than a mass -- the rate at which a short ton of ice melts over twenty-four hours -- and shows the arithmetic that produces the otherwise arbitrary 12,000 BTU per hour from the latent heat of fusion of ice.
Notes that a box marked 12,000 BTU means 12,000 BTU per hour, and that the dropped words are the difference between a quantity of heat and a rate -- the dimensional test being whether the number describes how fast or how much.
Separates cooling capacity from electricity consumed, which is the entire point of a heat pump: a 1.5 ton unit removes 5.28 kilowatts of heat while drawing about 1.3, so sizing a circuit, generator or solar system on the capacity over-specifies it three to five times.
Converts EER and COP exactly, since they are one measurement in two units differing only by the BTU-to-watt-hour factor, and reports the running current that follows from the power drawn rather than from the capacity.
Refuses to turn any seasonal rating into a COP: SEER, ISEER, the European SEER and SCOP are averages weighted over four different national load profiles, so no factor converts between them and a US SEER 18 cannot be compared with an Indian ISEER 5.
Says where the seasonal figures ARE the right comparison -- within one market, since they capture the part-load behaviour a single rating point misses, which is where an inverter unit earns its advantage.
Records the two BTU definitions in circulation and settles the question rather than leaving it open: they differ by 0.067 percent, a couple of watts on a five-kilowatt unit, and this page uses the International Table value.
Sets out the three market conventions -- India sizing in tons with ISEER stars, the United States in tons and BTU/h with SEER2, Europe and Australia in kilowatts with EN-standard seasonal figures -- and that capacity travels between them while seasonal efficiency does not.
States what the page is not: capacity conversion is not a load calculation, oversizing is a fault rather than a margin because a short-cycling unit dehumidifies badly, and the electrical figures are running load only and ignore starting current.
Verified by 51 automated cases, asserting the ton against its definition rather than a copied decimal, that every seasonal metric refuses to become a COP, and that at every realistic efficiency the power drawn is under half the heat removed.
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