CALTRX

BTU to Joules

Convert BTU to joules, kWh, and calories. 1 BTU = 1,055.06 J. For HVAC, heating, and cooling.

Enter your values above to see the results.

Tips & Notes

  • ✓12,000 BTU/hr = 1 ton of cooling = 3,517 watts — the key HVAC reference.
  • ✓For home sizing: approximately 20 BTU/hr per square foot of living space as a rough rule.
  • ✓Natural gas is sold in therms (1 therm = 100,000 BTU = 29.3 kWh).
  • ✓Energy Star ratings for appliances often show BTU — compare to kWh for electricity cost calculations.

Common Mistakes

  • ✗Confusing BTU (energy) with BTU/hr (power) — an AC uses BTU/hr, not BTU total.
  • ✗Using BTU/hr and watts interchangeably without conversion — 1 W ≠ 1 BTU/hr (1 W = 3.412 BTU/hr).
  • ✗Assuming all BTU definitions are equal — thermochemical BTU (1,054.35 J) vs IT BTU (1,055.06 J) differ slightly.
  • ✗Oversizing AC by BTU — an oversized AC short-cycles, reducing humidity control efficiency.

BTU to Joules Overview

What This Calculator Does

Converts BTU to and from joules, kilowatt-hours, and calories. 1 BTU = 1,055.06 J (IT definition — the standard for HVAC and engineering).

BTU Definition

1 BTU is the energy to raise 1 pound of water by 1°F. The IT BTU (1,055.06 J) is standard for HVAC. The thermochemical BTU (1,054.35 J) appears in some scientific texts — a 0.07% difference.

HVAC Sizing Reference

| BTU/hr | kW | Application | |--------|-----|-------------| | 5,000 | 1.46 | Small room AC (150 sq ft) | | 8,000 | 2.34 | Medium room (350 sq ft) | | 12,000 | 3.52 | 1 ton cooling (550 sq ft) | | 18,000 | 5.27 | Large room (700 sq ft) | | 36,000 | 10.55 | Whole-house unit |

Key: BTU/hr is power (rate). BTU alone is energy. 1 kWh = 3,412 BTU. 1 kW = 3,412 BTU/hr.

Frequently Asked Questions

1 BTU (IT) = 1,055.06 joules. The energy to raise 1 pound of water by 1°F.

12,000 ÷ 3.41214 = 3,517 watts = 3.517 kW. This is the standard 1-ton AC unit size.

1 BTU = 0.000293071 kWh. To convert: divide BTU by 3,412 for kWh.

1 ton of cooling = 12,000 BTU/hr. The term comes from the heat required to melt 1 short ton (2,000 lbs) of ice in 24 hours. 12,000 BTU/hr × 24 hr = 288,000 BTU = heat in 1 ton of ice.