What is a British Thermal Unit?

The British thermal unit is the standard for American HVAC systems, gas appliances, and air-conditioner ratings.

Overview

The British thermal unit (BTU) equals approximately 1,055.06 joules and is the standard unit in American HVAC, gas appliances, and air-conditioner ratings. Originally defined as the heat needed to raise 1 pound of water by 1°F, the BTU is the imperial counterpart to the calorie. American gas utilities measure delivered heat in BTUs or therms (1 therm = 100,000 BTU), and air conditioners are rated by their cooling capacity in BTU per hour (a typical window AC is 5,000–12,000 BTU/h, central AC for a medium home is 24,000–60,000 BTU/h). Furnaces are similarly rated. The BTU relates to the joule (1 BTU ≈ 1,055 J), the calorie (1 BTU ≈ 252 cal), the watt-hour (1 BTU ≈ 0.293 Wh), and the therm (100,000 BTU = 1 therm). Outside the United States, the BTU is rare; metric countries use kilojoules or kilowatt-hours for the same applications.

Symbol

BTU

Convert British Thermal Unit to all units

Live result

BTU

Joule1,055.0558 J Kilojoule1.055056 kJ Megajoule0.001055 MJ Kilowatt-Hour0.000293 kWh Watt-Hour0.293071 Wh Calorie252.1644 cal Kilocalorie0.252164 kcal Electronvolt6.585 × 10^21 eV Therm0.00001 thm

Relationship to Other Energy Units

1 BTU equals

Visual reference for how the british thermal unit relates to other energy units. Each row links to the full converter for that pair.

1 BTU=1,055.0558 J 1 BTU=1.055056 kJ 1 BTU=0.001055 MJ 1 BTU=0.000293 kWh 1 BTU=0.293071 Wh 1 BTU=252.1644 cal 1 BTU=0.252164 kcal 1 BTU=6.585 × 10^21 eV 1 BTU=0.00001 thm

When Is the British Thermal Unit Used?

US air-conditioner sizing
US heating-system capacity
Natural gas billing in some US regions

Real-world examples

Window AC: 5000–12,000 BTU/h. Central AC: 24,000–60,000 BTU/h. Home furnace: 60,000–100,000 BTU/h.

Tips for Using the British Thermal Unit

1 BTU = 1055.06 J = 0.293 Wh.
BTU/h (power) and BTU (energy) are different — don't confuse.
Tons of refrigeration: 12,000 BTU/h = 1 ton AC.

Common Mistakes

Confusing BTU and BTU/h — energy vs power.
Using kcal when BTU is requested in HVAC specs.
Treating all BTUs as exact — definitions vary (IT, thermochemical, etc.).

Convert British Thermal Unit to Other Energy Units

British Thermal Unit to Joule

1 BTU = 1,055.0558 J

British Thermal Unit to Kilojoule

1 BTU = 1.055056 kJ

British Thermal Unit to Megajoule

1 BTU = 0.001055 MJ

British Thermal Unit to Kilowatt-Hour

1 BTU = 0.000293 kWh

British Thermal Unit to Watt-Hour

1 BTU = 0.293071 Wh

British Thermal Unit to Calorie

1 BTU = 252.1644 cal

British Thermal Unit to Kilocalorie

1 BTU = 0.252164 kcal

British Thermal Unit to Electronvolt

1 BTU = 6.585 × 10^21 eV

British Thermal Unit to Therm

1 BTU = 0.00001 thm

Convert Other Units to British Thermal Unit

Joule to British Thermal Unit

1 J = 0.000948 BTU

Kilojoule to British Thermal Unit

1 kJ = 0.947817 BTU

Megajoule to British Thermal Unit

1 MJ = 947.81712 BTU

Kilowatt-Hour to British Thermal Unit

1 kWh = 3,412.1416 BTU

Watt-Hour to British Thermal Unit

1 Wh = 3.412142 BTU

Calorie to British Thermal Unit

1 cal = 0.003966 BTU

Kilocalorie to British Thermal Unit

1 kcal = 3.965667 BTU

Electronvolt to British Thermal Unit

1 eV = 1.519 × 10^-22 BTU

Therm to British Thermal Unit

1 thm = 100,000 BTU

FAQ About the British Thermal Unit

3 questions

What does the British Thermal Unit (BTU) measure?

The british thermal unit measures energy. The British thermal unit is the standard for American HVAC systems, gas appliances, and air-conditioner ratings.

When is the British Thermal Unit used?

The british thermal unit is used in: US air-conditioner sizing; US heating-system capacity; Natural gas billing in some US regions. Window AC: 5000–12,000 BTU/h. Central AC: 24,000–60,000 BTU/h. Home furnace: 60,000–100,000 BTU/h.

How accurate are conversions involving the British Thermal Unit?

All conversions on Units Converter use NIST SP 811 and BIPM reference values, accurate to 8 significant figures.