British thermal unit (BTU)

Definition

The (IT) British thermal unit, about 1055.06 joules.

History

The British thermal unit was defined as the heat needed to raise one pound of water by one degree Fahrenheit, making it the imperial counterpart of the calorie. It is about 1055 joules.

Where it is used

BTUs rate heating, air-conditioning and appliance output, especially in the United States.

Typical uses include heating and air conditioning, appliance ratings.

Conversion pages

These pages convert British thermal unit to or from another unit in energy.

• British thermal unit to kilowatt-hour
• British thermal unit to joule

Other Energy units

• Kilocalorie (kcal)
• Kilojoule (kJ)
• Calorie (cal)
• Joule (J)
• Kilowatt-hour (kWh)
• Watt-hour (Wh)

Sources

• NIST SP 811 NIST SP 811, Appendix B; ISO 80000-5 (energy) · Dataset reviewed Nov 11, 2026