How many BTU is one ton?

Exactly 12,000 BTU per hour. ASHRAE's terminology gives a ton of refrigeration as 12,000 BTU/h, approximately 3,517 watts. It is a definition rather than a measurement, so 2 tons is 24,000, 3 tons is 36,000 and 3.5 tons is 42,000, with no rounding anywhere in the chain.

Why is it called a ton at all?

Because it started as a literal ton of ice. Before mechanical refrigeration, cooling capacity was described by how much ice a system replaced in a day, and the unit stuck long after the ice trade ended. That is why a heating and cooling capacity is measured in a unit of weight, and why it sounds strange to anybody meeting it on a quote for the first time.

Is a 2 ton heat pump the same as a 2 ton air conditioner?

In nameplate capacity, yes: both mean 24,000 BTU per hour at the rating conditions. What differs is what happens away from those conditions. An air conditioner is rated for cooling and only ever cools. A heat pump has a heating capacity as well, and that heating capacity falls as the outdoor temperature falls, so a 2 ton heat pump does not deliver 24,000 BTU/h of heat on a January night in Toronto. The nameplate is a starting point, not a promise.

What size is my house in tons?

Ontario Heat Loss publishes 20,000 to 26,000 BTU per hour of design heat loss for a well built 2,000 square foot house in the GTA, which is 1.7 to 2.2 tons. That figure surprises people who have seen a 5 ton furnace quoted for the same house. Both numbers are real; one is the building's measured heat loss and the other is what a rate per square foot suggests.

Why are systems sold in half ton steps?

Because manufacturers build to catalogue sizes and the market quotes those sizes. The sourced price rows on this site name a 2 ton heat pump, a 3 ton outdoor unit and a 3.5 to 4 ton system, which is what the steps look like in practice. It means a house whose real load works out at 2.2 tons is choosing between a 2 and a 2.5, and which way that choice goes is a conversation about the coldest hours rather than a rounding rule.

BTU, Tons, Kilowatts: The Same Number Three Ways

Last updated: August 25, 2026By HeatPumpIndex Evidence Desk

Quotes in this market are written in tons, spec sheets in BTU per hour and electric backup elements in kilowatts, which makes comparing two of them harder than it needs to be. Put in whichever you have and this gives you the other three, plus the catalogue sizes either side of it.

One capacity, four ways of writing it

Capacity

Whatever number is written on the quote, the label or the spec sheet.

Written in

BTU per hour (BTU/h)Tons of refrigeration (tons)Kilowatts (kW)Watts (W)

Two definitions do all of this. A ton of refrigeration is 12,000 BTU/h, and one watt is 3.412142 BTU/h. Neither is an estimate of anything.

The same capacity

BTU per hour: 24,000
Tons of refrigeration: 2.000
Kilowatts: 7.034
Watts: 7,034

Where that sits in the sizes people quote

Exactly 2.0 tons, which is a size quoted as it stands.

ASHRAE gives the ton as 12,000 BTU/h and approximately 3,517 W. Converted exactly through 3.412142 BTU/h per watt it comes to 3516.85 W, so the two differ in the fourth figure. This page uses the exact conversion and tells you what ASHRAE rounds it to.

What a ton means on a Toronto quote

It means nameplate capacity at rating conditions, and it is the number the catalogue is organised by rather than a description of what the machine will do at your house in February. Equipment is built and quoted in whole and half ton steps. The sourced price rows HeatPumpIndex keeps name a 2 ton heat pump, a 3 ton outdoor unit and a 3.5 to 4 ton system, and that is what the market actually offers.

So the practical use of a conversion is comparing things that were written down differently. A heat loss calculation comes back in BTU per hour. A quote says three tons. An electric backup element is labelled in kilowatts, and the electrician cares about the amps that implies. All four describe the same physical quantity and none of the three trades involved writes it the same way.

One thing a nameplate does not tell you is what a heat pump delivers when it is cold. A two ton air conditioner moves two tons of heat whenever it runs. A two ton heat pump has two tons of heating capacity at its rating conditions and less as the outdoor temperature drops, which is why heat pump quotes talk about balance points and air conditioner quotes do not.

Where the unit came from, and why it is a unit of weight

Before mechanical refrigeration, cooling was bought as ice. A building’s cooling requirement was described by how much ice it went through in a day, and when machines replaced the ice they were rated by how much ice they displaced. One ton of refrigeration is the rate of cooling that would melt one short ton of ice over twenty-four hours. The arithmetic lands on 12,000 BTU per hour, and the name outlived the trade that produced it.

ASHRAE’s terminology keeps both figures, the BTU one and the watt one, and the watt one is where a small inconsistency lives. It gives the ton as approximately 3,517 watts. Converting through the definition of the watt, 3.412142 BTU per hour each, gives 3516.85. Four parts in ten thousand apart, which never matters for choosing equipment and is worth understanding so that two sources disagreeing does not read as one of them being wrong.

This converter uses the exact path in every direction: whatever you type is turned into BTU per hour first and then into the other units, so tons to kilowatts and kilowatts to tons come back to where they started rather than drifting a little each time.

Frequently asked questions

How many BTU is one ton?: Exactly 12,000 BTU per hour. ASHRAE's terminology gives a ton of refrigeration as 12,000 BTU/h, approximately 3,517 watts. It is a definition rather than a measurement, so 2 tons is 24,000, 3 tons is 36,000 and 3.5 tons is 42,000, with no rounding anywhere in the chain.
Why is it called a ton at all?: Because it started as a literal ton of ice. Before mechanical refrigeration, cooling capacity was described by how much ice a system replaced in a day, and the unit stuck long after the ice trade ended. That is why a heating and cooling capacity is measured in a unit of weight, and why it sounds strange to anybody meeting it on a quote for the first time.
Why does the watt figure differ depending on where I look?: Because two conventions collide in the fourth significant figure. ASHRAE quotes the ton as approximately 3,517 watts. Converting the same ton exactly through the definition of the watt, 3.412142 BTU per hour each, gives 3516.85 watts. The difference is about four parts in ten thousand and it never matters for sizing equipment, but it is worth knowing why two sources can both be right and disagree.
Is a 2 ton heat pump the same as a 2 ton air conditioner?: In nameplate capacity, yes: both mean 24,000 BTU per hour at the rating conditions. What differs is what happens away from those conditions. An air conditioner is rated for cooling and only ever cools. A heat pump has a heating capacity as well, and that heating capacity falls as the outdoor temperature falls, so a 2 ton heat pump does not deliver 24,000 BTU/h of heat on a January night in Toronto. The nameplate is a starting point, not a promise.
What size is my house in tons?: Ontario Heat Loss publishes 20,000 to 26,000 BTU per hour of design heat loss for a well built 2,000 square foot house in the GTA, which is 1.7 to 2.2 tons. That figure surprises people who have seen a 5 ton furnace quoted for the same house. Both numbers are real; one is the building's measured heat loss and the other is what a rate per square foot suggests.
Why are systems sold in half ton steps?: Because manufacturers build to catalogue sizes and the market quotes those sizes. The sourced price rows on this site name a 2 ton heat pump, a 3 ton outdoor unit and a 3.5 to 4 ton system, which is what the steps look like in practice. It means a house whose real load works out at 2.2 tons is choosing between a 2 and a 2.5, and which way that choice goes is a conversation about the coldest hours rather than a rounding rule.

Sources

Once you have the number in the right unit

A capacity on its own does not tell you whether it suits the house. The sizing calculator puts it beside published design heat loss for your climate region, and the room calculator does the same job one room at a time.

Check it against your house Size a single room