Ton to kW Converter

kW = RT × 3.5168528, from 1 RT = 12,000 BTU_IT/h and 1 BTU_IT = 1055.05585262 J

RT

The refrigeration ton, the unit this page starts from and the one that causes the most confusion. It is a power, not a mass: it is the rate at which heat has to be removed to freeze one short ton of water at 0 °C in 24 hours, and the short ton here is 2000 pounds, about 907 kilograms. Nothing on this page is measured in pounds or kilograms. If you arrived expecting a weight conversion, the mass tables are a different set of pages

12000

The number of BTU per hour in one refrigeration ton, and it is a definition rather than a conversion. It falls out of the original arithmetic: melting a pound of ice takes about 144 BTU, so 2000 pounds takes 288,000 BTU, and spread over 24 hours that is exactly 12,000 BTU per hour. That is why the ton is 12,000 rather than some round metric figure — the definition is American, and it survived because air conditioning grew up in that market

3.5168528

The same ton expressed in kilowatts: 12,000 BTU per hour converted through joules, 12,000 × 1055.05585262 / 3600 = 3516.8528 W. It is a repeating decimal, so every published figure is a rounded version of this one — 3.517 and 3.52 are the same number written more loosely, and only the fourth decimal place tells them apart. That is why the results here carry four decimals

EER

The energy efficiency ratio, and the reason this page insists on saying which power it is answering with. Cooling capacity divided by EER gives the electrical input power, so a one-ton unit rated at EER 11.5 draws about 1.04 kW at the plug: 12,000 / 11.5 = 1043 W. The higher the EER, the less electricity buys the same cooling, and a heat pump rating in COP is the same idea without the unit conversion. The page does not ask for it because the conversion does not need it, but every capacity figure here is cooling and never consumption

Btu_IT

The British thermal unit on the International Table, 1055.05585262 joules, which is the definition this page uses. There is a second one, the thermochemical Btu at 1054.350 joules, and the two differ by about 0.07 per cent — far below the tolerance on any capacity figure quoted in practice, but they are not the same number and mixing them is a real, if small, error. Air conditioning capacity is normally quoted on the International Table

Use this calculator whenever a cooling capacity arrives in a unit you cannot compare against anything else you have: an American datasheet in BTU per hour, a Chinese sales listing in a unit called pi that means roughly 2.5 kW, a European one in kilowatts, and a chiller nameplate in refrigeration tons. They are all the same quantity, and because this is a conversion between definitions rather than a measurement, nothing about it is approximate — one ton is 3.5168528 kW by construction. It is also the step before the electrical question. Once the cooling capacity is known, the watts to amps calculator turns the unit's input power into the current it will draw from the supply, and that is what sizes the cable and the breaker.

1. The definition line: one refrigeration ton

   1. One refrigeration ton is 12,000 BTU per hour, by definition
   2. Convert to joules per hour: 12,000 × 1055.05585262 = 12,660,670.23 J/h
   3. Convert to joules per second and that is watts: 12,660,670.23 / 3600 = 3516.8528 W
   4. Divide by 1000 and the answer is 3.5169 kW

   Both middle rows of the result panel are interesting here and neither is a rounding artefact. The 12000 BTU per hour row is the definition itself, unchanged, because the ton was defined that way and every other figure on the page is derived from it. The 3.5169 kW row is the same number in metric clothing, and it is the one an international reader will quote. If a datasheet says 3.52 kW and this page says 3.5169, they agree: the datasheet rounded.

2. A three-ton air conditioner, the commonest size in North American homes

   1. Three refrigeration tons is 3 × 12,000 = 36,000 BTU per hour
   2. Divide by 3412.1416 BTU per hour per kW, and 36,000 / 3412.1416 = 10.5506 kW
   3. Or take the single-ton figure and multiply: 3 × 3.5168528 = 10.5506 kW
   4. As an electrical load at EER 11.5 that is 36,000 / 11.5 = 3130 W, near enough 3.1 kW

   Read the last step against the first, because that gap is the point of the page. The unit is sold as three tons and is 10.55 kW of cooling, and it will pull around 3.1 kW from the socket — a third as much, because a heat pump moves heat instead of making it. Anyone who sizes a circuit from the cooling figure will install cable and a breaker three times larger than needed; anyone who assumes the electrical figure is the capacity will undersize the air conditioning. The lookup table below lists the sizes between half a ton and a hundred tons, so a nameplate figure can be found in it directly.

3. One and a half tons, the size most North American homes actually get

   1. One and a half refrigeration tons is 1.5 × 12,000 = 18,000 BTU per hour
   2. Multiply the kilowatt figure for one ton: 1.5 × 3.5168528 = 5.2753 kW
   3. Check the reverse: 5.2753 kW × 3412.1416 / 12,000 = 1.5000 tons
   4. As a load at EER 11.5 that is 18,000 / 11.5 = 1565 W

   Half-ton steps are the practical resolution of this market, which is why the table below carries 0.5, 0.75, 1, 1.5, 2 and 3 before it jumps. If your figure came from a metric nameplate instead, switch the unit to kW and type the number from the label — 2.5 kW entered directly comes back as 0.7109 tons, which is the quotient 2500 / 3516.8528 and not a separate calculation. The unit dropdown exists for exactly that, and the base unit of the input only decides what the box opens with.

4. A hundred-ton chiller, read off a nameplate in metric

   1. A hundred refrigeration tons is 100 × 12,000 = 1,200,000 BTU per hour
   2. In kilowatts: 100 × 3.5168528 = 351.6853 kW
   3. Or from the BTU figure: 1,200,000 / 3412.1416 = 351.6853 kW
   4. The input was typed as 351.6853 kW with the unit dropdown set to kW, and the page restated it in tons

   At this size the ton is the unit on the selection sheet and kilowatts is the unit in the tender document, and a chiller plant is where the two meet most often. Nothing changes in the arithmetic at either end of the range, which is worth knowing because the multipliers are easy to misremember: 3.517 rather than 3.5 is a 0.5 per cent error, and on a 350 kW machine that is a megawatt-hour a month of cooling nobody accounted for. This page recomputes from the definitions every time rather than applying a remembered factor.

The page converts a cooling capacity and does nothing else. It does not size a unit for a room, because the cooling load depends on floor area, ceiling height, glazing, orientation, insulation, local climate and how many people are in the space, and none of those are inputs here: a rule of thumb such as 100 to 150 W per square metre is not applied and cannot be read off this page. Capacity figures are nominal ratings at standard rating conditions, and a unit delivers less than its rating when the outdoor temperature climbs well above them. The ton here is the refrigeration ton only — the short ton, the long ton and the tonne are masses and live in the mass tables. The Btu used is the International Table one, and the thermochemical Btu differs by about 0.07 per cent.

Is a refrigeration ton a unit of weight?

No. It is a unit of power, and the name is a leftover from how it was originally defined: the rate at which heat must be removed to freeze one short ton of water at 0 °C in 24 hours. The weight is part of the definition, not part of the answer. A refrigeration ton is 12,000 BTU per hour, which is 3.5168528 kW, and the short ton, the long ton and the tonne — the actual weights — are handled by the mass conversion pages instead.

Why is one ton exactly 12,000 BTU per hour?

Because the unit was built from ice. Melting a pound of ice takes about 144 BTU of latent heat, so 2000 pounds takes 2000 × 144 = 288,000 BTU, and spreading that over 24 hours gives 288,000 / 24 = 12,000 BTU per hour. The arithmetic is deliberately round in BTU per day, which is why the metric figure it converts to is not round at all. Every other number on this page descends from that one.

Is this the electricity the air conditioner uses?

No, and this is the mistake the page exists to prevent. What you entered and what it returns is cooling capacity: heat removed from the room. The electrical input power is cooling capacity divided by the energy efficiency ratio, so a three-ton unit is 10.55 kW of cooling and about 3.1 kW of electricity at EER 11.5. Sizing a circuit from the cooling figure gives cable and a breaker around three times larger than the installation needs.

How does this compare with an air conditioner sold by pi in China?

Pi is a trade shorthand rather than a defined unit, and it is used to mean roughly 2500 W of cooling capacity for one pi. On that convention, one refrigeration ton of 3.5169 kW is about 1.4 pi, and the common Chinese sizes of 1, 1.5 and 2 pi are roughly 2.5, 3.5 and 5 kW. Because pi is a sales label and not a definition, this page does not offer it as an input unit; convert through watts or kilowatts instead, which is what the nameplate carries.

Which BTU does the page use?

The International Table Btu, 1055.05585262 joules, which is the one air conditioning capacity is normally quoted on. The thermochemical Btu is 1054.350 joules, about 0.07 per cent smaller, and using it here would move the kilowatt figure in the fifth decimal place. Both are in the conversion tables, and the difference is far below the precision of any capacity figure a manufacturer publishes, but the page states which one it used rather than leaving it to be guessed.

Why is the answer exact?

Because nothing in it is measured. One refrigeration ton is defined as 12,000 BTU per hour, the International Table Btu is defined as 1055.05585262 joules, and an hour is 3600 seconds; the only operations are multiplication and division on defined quantities. A real air conditioner's delivered capacity is a measurement and varies with conditions, but the conversion between the units has no uncertainty in it at all, so the numbers here are correct to as many places as they are shown.

Can I enter a figure in kilowatts or BTU per hour?

Yes. The input has a unit selector covering refrigeration tons, kilowatts, watts and BTU per hour, and the conversion runs in either direction. The box opens in refrigeration tons because that is what the page is named for, and the answer panel always restates the value in all three of tons, kilowatts and BTU per hour, so a figure from any source can be checked against the others without a second calculation.

• Ton of refrigeration — the 12,000 BTU per hour definition, how melting a short ton of ice in 24 hours produces it, and why the unit is still standard in North American air conditioning — Wikipedia
• NIST Special Publication 811, Guide for the Use of the International System of Units (SI), Appendix B.8 — the conversion factors used here, including the International Table Btu of 1055.05585262 J — National Institute of Standards and Technology
• British thermal unit — the International Table and thermochemical definitions, which differ by about 0.07 per cent, and where each is used — Wikipedia