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Converter · Capacity units
BTU to tons converter
A ton of air conditioning is 12,000 BTU per hour, about 3.517 kW. Enter a capacity in any of the five units and the converter returns the other four, using the conversion factors published by NIST.
- Choose BTU/h, tons, kW, watts or MBH, whichever the data sheet or load report uses.
- Type the rate of heat from the nameplate, the submittal or the load calculation.
- The result shows tons, BTU/h and kW on top, with watts and MBH below.
Example result for the default inputs
36,000 BTU/h converted to every unit
Tons of refrigeration
3.000 tons
BTU per hour
36,000 BTU/h
Kilowatts
10.55 kW
| Watts | 10,551 W |
|---|---|
| MBH | 36.00 MBH |
| BTU per minute | 600.0 BTU/min |
| Kilocalories per hour | 9,072 kcal/h |
| Factors used | 1 ton = 12,000 BTU/h, 1 BTU/h = 0.2930711 W, 1 kcal/h = 1.163 W (NIST SP 811) |
For estimation purposes only. Consult a licensed engineer for final designs.
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How the conversion works
Every unit goes through BTU per hour first. A ton is a fixed number of BTU/h, and a watt is a fixed fraction of one, so each answer is one multiplication or one division away from the number you typed.
- Tons from BTU/h
tons = BTU/h / 12,000NIST SP 811 lists the ton of refrigeration as 12,000 BTU per hour (IT). It is a rate, the same way BTU/h and watts are.- Watts from BTU/h
W = BTU/h x 0.2930711, kW = W / 1,000The factor 0.2930711 is the NIST SP 811 conversion from BTU (IT) per hour to watts. Going the other way, 1 kW is about 3,412 BTU/h.- Watts from tons
W = tons x 3,516.853NIST SP 811 gives 3,516.853 W per ton of refrigeration, which is 12,000 x 0.2930711. The converter uses the BTU/h route, and the two agree.- MBH
MBH = BTU/h / 1,000MBH means thousand BTU per hour. It is how many submittals and commercial data plates print capacity, so 60 MBH is 60,000 BTU/h, or 5 tons.- BTU per minute
BTU/min = BTU/h / 60An hour has 60 minutes, so 36,000 BTU/h is 600 BTU/min. Some older commercial and process equipment is rated this way.- Kilocalories per hour
kcal/h = W / 1.163NIST SP 811 puts the IT kilocalorie at 4,186.8 J. Spread over the 3,600 seconds of an hour, 1 kcal/h is 1.163 W. Asian and European data sheets often print capacity in kcal/h.
Capacities you see on real equipment
Each row starts from the unit the equipment is usually listed in and converts it the same way the form does.
| Equipment | Tons | BTU/h | kW |
|---|---|---|---|
| Wall-mount mini split head, 12,000 BTU/h | 1.000 | 12,000 | 3.517 |
| Residential condenser, 3 tons | 3.000 | 36,000 | 10.55 |
| Heat pump data sheet in kW, 5 kW | 1.422 | 17,061 | 5.000 |
| Rooftop unit submittal, 60 MBH | 5.000 | 60,000 | 17.58 |
| Small commercial chiller, 20 tons | 20.00 | 240,000 | 70.34 |
The kW column is heat moved, not electricity drawn. One kW of capacity is 3,412 BTU/h, so a heat pump sheet that lists 5 kW is a unit a little over a ton and a third. The electric power the unit draws is a separate number that depends on its efficiency rating.
Standards and data sources
- NIST Special Publication 811, Guide for the Use of the International System of Units, Appendix B.8 - the factors 1 BTU (IT) per hour = 0.2930711 W and 1 ton of refrigeration (12,000 BTU per hour) = 3,516.853 W, and the IT kilocalorie = 4,186.8 J, which gives 1 kcal/h = 1.163 W.
- Equipment data plates and manufacturer submittals - where the capacity you convert comes from. Use the rated capacity at the conditions the manufacturer lists, not the number in the model name.
Limitations of this converter
- This page converts units of a heat rate. It does not size equipment and does not turn floor area into tons.
- A nominal ton on a residential condenser is a size class. The rated capacity printed in the manufacturer's data can be a little above or below 12,000 BTU/h per nominal ton, and real output moves with outdoor temperature, indoor airflow and charge.
- Heating and cooling use the same BTU/h. A furnace input rating is fuel burned, not heat delivered, so convert the output rating if you are comparing heat into the house.
- Results are rounded for display. The conversion itself uses the full factors.
Common unit mistakes on HVAC jobs
- Reading the model number as the capacity. Many residential model numbers carry a size code such as 024, 036 or 048. That is a nominal size class. The rated capacity in the manufacturer's data is the number to convert and compare.
- Treating a ton as a weight. A ton of refrigeration is a rate of heat removal, 12,000 BTU every hour. It has nothing to do with how much the unit weighs, and it is not a quantity of energy you can store.
- Dividing square feet by a rule of thumb and calling it tons. Square feet per ton rules ignore insulation, windows, orientation and climate. Use a load calculation for size, then come back here if you need the answer in another unit.
- Mixing up kW of capacity and kW of power draw. A 3-ton air conditioner moves about 10.5 kW of heat but draws far less electric power, because a compressor moves more heat than it uses. The ratio is the efficiency rating, not a unit conversion.
- Mixing up MBH and MMBH. MBH is thousand BTU/h. Boiler and process literature sometimes uses MMBH for million BTU/h, a factor of a thousand apart. Check which one the sheet means before converting.
Common questions about BTU, tons and kW
How many BTUs are in a ton of air conditioning?
12,000 BTU per hour. NIST SP 811 defines the ton of refrigeration as 12,000 BTU (IT) per hour, so a 3-ton system is 36,000 BTU/h and a 5-ton system is 60,000 BTU/h.
How do I convert BTU to tons?
Divide BTU per hour by 12,000. 24,000 BTU/h is 2 tons, 42,000 BTU/h is 3.5 tons. The number has to be a rate in BTU per hour, the way capacity is rated, not a total amount of energy.
How many kW is a ton of cooling?
3.516853 kW. NIST SP 811 gives 3,516.853 W per ton of refrigeration. A 3-ton unit is about 10.55 kW of cooling capacity, which is heat moved, not electricity used.
How do I convert kW to BTU per hour?
Multiply by about 3,412.14, which is 1,000 divided by the NIST factor 0.2930711. A 5 kW heat pump rating is about 17,061 BTU/h, a little over 1.4 tons.
What does MBH mean on a data plate?
Thousand BTU per hour. 36 MBH is 36,000 BTU/h, or 3 tons. It is common on commercial equipment, boilers and submittal sheets.
Why does my 3-ton unit not put out exactly 36,000 BTU/h?
Nominal tons are a size class. Capacity is rated at one standard test condition, and the manufacturer's data shows how it changes with outdoor temperature and indoor airflow. On a hot afternoon a unit can deliver less than its nominal size.
How many tons do I need for my house?
This converter cannot tell you, because size depends on the load, not on a unit. Run the Manual J calculator or the what size AC page, then convert the result here if you need it in kW or MBH.
Used on the same job
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Converting a number does not tell you whether it is the right size. Describe the house in chat and the assistant runs the free whole-house Manual J heating and cooling load, in BTU/h and tons.
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