CALTRX

BTU to Joules

Convert BTU to joules for thermodynamics and international engineering. 1 BTU = 1,055.06 J — enter any BTU value for joules with heat transfer and energy context.

Enter your values above to see the results.

Tips & Notes

  • ✓BTU/hr vs BTU: BTU/hr is power (rate of energy flow); BTU is energy quantity. A furnace rated at 80,000 BTU/hr delivers that heat rate continuously. In SI: 80,000 BTU/hr × 1,055.06 J/BTU ÷ 3,600 s/hr = 23,457 W = 23.46 kW.
  • ✓AC and heating efficiency: COP (Coefficient of Performance) = energy output (J) / energy input (J). A heat pump with COP 3.5 delivers 3.5 J of heat per 1 J of electrical input = 350% efficiency. SEER for AC: SEER 16 = 16 BTU of cooling per watt-hour = 16 BTU / (1 Wh × 3,412 BTU/kWh) × 1,000 = 4.69 W of cooling per W electrical.
  • ✓One BTU is a small amount of energy: it is the heat released by burning one kitchen match. A gas stove burner on high releases about 9,000 BTU/hr = 9,475,000 J/hr = 2,638 W. A home furnace at 100,000 BTU/hr = 29,307 W = 29.3 kW.
  • ✓British thermal units come in several variants: IT BTU (International Table, 1,055.0559 J) is the most common; Thermochemical BTU (1,054.35 J); ISO BTU (1,055.87 J). For most engineering calculations, use 1,055.06 J unless a specific standard is specified.
  • ✓Steam tables: engineers use BTU for enthalpy (heat content per unit mass) and BTU/lb for specific enthalpy. Steam at 212°F (100°C) has a specific enthalpy of approximately 1,150 BTU/lb = 1,150 × 1,055.06 / 0.453592 = 2,675,000 J/kg = 2,675 kJ/kg.

Common Mistakes

  • ✗Confusing BTU/hr (power) with BTU (energy) — these are different quantities. A 3-ton AC (36,000 BTU/hr of cooling) consumes 36,000 BTU/hr, not 36,000 BTU. To find joules of energy over time: J = (BTU/hr) × 1,055.06 × hours.
  • ✗Using the wrong BTU variant for precision calculations — IT BTU (1,055.0559 J) and thermochemical BTU (1,054.35 J) differ by 0.067%. For most engineering, use IT BTU. For food science and chemistry, use thermochemical BTU (or convert via thermochemical calorie = 4.184 J).
  • ✗Converting BTU to joules and then forgetting the scale — 1 BTU = 1,055 J. A 100,000 BTU furnace produces 100,000 × 1,055 = 105,500,000 J = 105.5 MJ per hour. At this scale, megajoules (MJ) or kilowatt-hours (kWh) are more practical: 105.5 MJ / 3,600 s = 29.3 kW.
  • ✗Applying BTU-to-joule conversion to BTU/lb (specific enthalpy) — BTU/lb is a specific energy unit (energy per unit mass). Converting to J/kg requires: 1 BTU/lb = 1,055.06 J / 0.453592 kg = 2,326 J/kg. The extra ÷ 0.453592 accounts for the pound-to-kilogram mass conversion.
  • ✗Forgetting that 1 kWh = 3,412 BTU (not 3,600) — this is a common confusion. 1 kWh = 1 kW × 1 hour = 1,000 W × 3,600 s = 3,600,000 J = 3,600,000 / 1,055.06 = 3,412.1 BTU. The 3,600 is the J/kWh value, not the BTU/kWh value.

BTU to Joules Overview

The BTU is the thermal engineering unit of the US system — found in furnace ratings, AC efficiency specs, natural gas billing, and building energy codes. Converting to joules (the SI unit of energy) is required for international engineering, scientific calculations, and cross-system energy comparisons.

BTU to joules formula:

J = BTU × 1,055.06 | 1 BTU = 1,055.06 J = 0.293071 Wh | 1 kWh = 3,412 BTU
EX: 80,000 BTU/hr furnace → energy in 1 hr: 80,000 × 1,055.06 = 84,404,800 J = 84.4 MJ = 23.45 kWh. Water heater 50,000 BTU/hr → power: 50,000 × 0.293071 = 14,654 W = 14.65 kW
Inverse — joules to BTU:
BTU = J / 1,055.06 | BTU = J × 0.000947817
EX: 1 kWh = 3,600,000 J / 1,055.06 = 3,412.1 BTU. Home heating: 70 MJ daily = 70,000,000 / 1,055.06 = 66,351 BTU/day
Energy unit comparison — BTU and joules:
Energy QuantityBTUJouleskWh
1 BTU11,055 J0.000293 kWh
1 therm (natural gas)100,000105.5 MJ29.3 kWh
1 kWh (electricity)3,4123.6 MJ1
1 gallon gasoline~125,000~131.9 MJ~36.6 kWh
1 cubic foot natural gas1,0201.076 MJ0.299 kWh
1 food Calorie (kcal)3.9664,184 J0.00116 kWh
HVAC equipment ratings in BTU/hr and kW:
EquipmentBTU/hrkW (power)Notes
Window AC (small)5,0001.465 kW1-room cooling
Window AC (large)12,000 (1 ton)3.517 kW1 ton = 12,000 BTU/hr
Central AC (3-ton)36,00010.55 kWTypical home
Gas furnace (small)60,00017.58 kWOutput at 95% AFUE
Gas furnace (large)120,00035.17 kWLarge home
Boiler (commercial)500,000146.5 kWSmall commercial
The BTU-to-joule conversion reveals the enormous scale of HVAC energy: a "small" 60,000 BTU/hr furnace delivers 60,000 × 1,055.06 J = 63,303,600 J per hour = 17.58 kW of heat — enough to heat 17 one-kilowatt space heaters running simultaneously. Understanding both BTU and joule scales allows engineers to move fluently between US mechanical engineering (furnace ratings, building codes, gas billing) and the SI-based physics and thermodynamics that underpin all energy calculations.

Frequently Asked Questions

Multiply BTU by 1,055.06. Examples: 1 BTU = 1,055.06 J; 100 BTU = 105,506 J = 105.5 kJ; 1,000 BTU = 1,055,060 J = 1.055 MJ; 10,000 BTU = 10.55 MJ; 100,000 BTU = 105.5 MJ. Reverse: J / 1,055.06 = BTU. Key equivalence: 1 BTU = 1,055.06 J = 252.164 cal = 0.293071 Wh = 0.000293071 kWh.

A British Thermal Unit (BTU) is the amount of heat energy required to raise the temperature of one pound of water by one degree Fahrenheit at maximum density. It was defined in the 19th century for steam engineering and became the standard for HVAC, refrigeration, and combustion calculations in the US and UK. HVAC equipment is rated in BTU/hr (BTU per hour) for cooling and heating capacity. One BTU/hr = 0.293071 W. A 5,000 BTU/hr window AC = 5,000 × 0.293071 = 1,465 W of cooling capacity. The unit persists in US engineering despite global SI adoption due to embedded standards, codes, and industry practice.

Energy comparisons: 1 food Calorie (kcal) = 1,000 cal = 4,184 J = 3.966 BTU; 1 kWh = 3,600,000 J = 3,412 BTU; 1 therm (natural gas) = 100,000 BTU = 105,506,000 J = 105.5 MJ = 29.3 kWh; 1 gallon of gasoline ≈ 125,000 BTU = 131.9 MJ = 36.6 kWh; 1 cubic foot of natural gas = 1,020 BTU = 1,076 kJ; average US home heating per year ≈ 70,000,000 BTU = 73.9 GJ = 20.5 MWh. For everyday energy amounts, kWh is more intuitive than joules or BTU.

Power conversion: 1 BTU/hr = 0.293071 W = 0.000293071 kW. Formula: kW = BTU/hr × 0.000293071. Examples: 40,000 BTU/hr furnace = 40,000 × 0.000293071 = 11.72 kW; 80,000 BTU/hr = 23.45 kW; 100,000 BTU/hr = 29.31 kW; 150,000 BTU/hr = 43.96 kW. Reverse: BTU/hr = kW / 0.000293071 = kW × 3,412.1. A 10 kW electric heater = 10 × 3,412.1 = 34,121 BTU/hr output. Note: furnace efficiency (AFUE) means input BTU/hr is higher than output: a 95% AFUE 80,000 BTU output furnace consumes 80,000/0.95 = 84,211 BTU/hr of gas.

Thermodynamic calculations in US engineering use BTU; international and scientific work uses joules and kilojoules. Specific heat of water: 1 BTU/lb/°F = 4,186.8 J/kg/K. Enthalpy of vaporization of water at 100°C: 970.3 BTU/lb = 970.3 × 2,326 J/kg = 2,256,878 J/kg ≈ 2,257 kJ/kg. Heat transfer rate: Q (BTU/hr) = U (BTU/hr/ft²/°F) × A (ft²) × ΔT (°F). Converting to SI: Q (W) = U (W/m²/K) × A (m²) × ΔT (K). The U-value conversion: 1 BTU/hr/ft²/°F = 5.678 W/m²/K.

Three different "calorie" quantities create confusion: 1 small calorie (cal) = energy to raise 1 g of water by 1°C = 4.184 J = 0.003966 BTU; 1 food Calorie (Cal or kcal) = 1,000 small calories = 4,184 J = 3.966 BTU; 1 BTU = 252.164 small calories = 0.252164 kcal (food Calories). Food labeling: a 100 Calorie snack contains 100 kcal = 418,400 J = 396.6 BTU of metabolic energy. Engineering BTU: a 10,000 BTU/hr AC removes 10,000 × 252.164 = 2,521,640 cal/hr = 2,521.6 kcal/hr = 2,930.7 W of heat. The food calorie is 3.966× a BTU; the engineering BTU is 252× a chemistry calorie.