FreeHVACCalculators

BTU to Tons Converter

Convert heating and cooling capacity between BTU per hour, tons of refrigeration, kilowatts and other units.

Method reviewed October 22, 2026. Version 1.0.0. How it works

Your inputs

Result

BTU/h
36,000BTU/h
Tons of refrigeration
3tons
Kilowatts (kW)
10.55kW

36,000 BTU/h = 36,000 BTU/h = 3 tons = 10.551 kW.

MBH (1,000 BTU/h)
36MBH
Watts (W)
10,551W
kcal/h
9,072kcal/h
Mechanical horsepower (hp)
14.15hp
Boiler horsepower (BHP)
1.075BHP
Show the working
  1. Convert to BTU/h
    36,000 × 1 = 36,000 BTU/h
  2. Tons = BTU/h ÷ 12,000
    36,000 / 12,000 = 3 tons
  3. kW = BTU/h × 0.29307107 ÷ 1,000
    36,000 × 0.29307107 / 1,000 = 10.5506 kW

The conversions

  • 1 ton of refrigeration = 12,000 BTU/h — the heat needed to melt one short ton of ice in 24 hours.
  • 1 kW = 3,412.14 BTU/h, and 1 BTU/h = 0.29307 W (NIST).
  • 1 MBH = 1,000 BTU/h, common on boiler and furnace spec sheets.
  • 1 boiler horsepower = 33,475 BTU/h; 1 mechanical horsepower = 2,544 BTU/h.

So a 3-ton air conditioner is 36,000 BTU/h, or about 10.55 kW of cooling.

Capacity versus power

A “3.5 kW” air conditioner sold in Europe or Australia is usually rated by its cooling output — about 12,000 BTU/h, or one ton — not by the electricity it uses. The electrical input is several times smaller, set by the unit’s efficiency. Check which figure a specification is quoting before converting.

Worked example

These are the example values the calculator opens with, and the result the engine calculates for them.

Inputs

Value
36,000
From
BTU/h

Result

BTU/h
36,000 BTU/h
MBH (1,000 BTU/h)
36 MBH
Tons of refrigeration
3 tons
Kilowatts (kW)
10.55 kW
Watts (W)
10,551 W
kcal/h
9,072 kcal/h

36,000 BTU/h = 36,000 BTU/h = 3 tons = 10.551 kW.

Assumptions

  • Uses the International Table BTU (1 BTU = 1,055.05585262 J) and 1 ton of refrigeration = 12,000 BTU/h.
  • kcal/h uses the International Table calorie (4.1868 J).

Limitations

  • Equipment “tonnage” on a model number is nominal; delivered capacity depends on operating conditions.

Frequently asked questions

How many BTUs is a 2-ton AC?

24,000 BTU/h. Multiply tons by 12,000 to get BTU/h.

Why is it called a ton?

It comes from the era of ice cooling: one ton of refrigeration is the cooling effect of melting one short ton (2,000 lb) of ice over 24 hours, which works out to 12,000 BTU per hour.

Sources

  1. NIST Guide to the SI (SP 811), Appendix B.9 — conversion factors — National Institute of Standards and Technology. 1 ton of refrigeration = 12,000 BTU/h; 1 BTU/h = 0.2930711 W; 1 atm = 101.325 kPa.
  2. Energy explained — British thermal units (Btu) — U.S. Energy Information Administration. 100,000 Btu per therm; 1,036 Btu/ft³ natural gas; 91,452 Btu/gal propane; 138,500 Btu/gal heating oil; 3,412 Btu/kWh.

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