Energy Converter
Convert between joules, kilowatt-hours, calories, BTU, electronvolts and more instantly. Covers electricity bills, nutrition, heating and scientific applications.
| From | To Joules (J) | Context |
|---|---|---|
| 1 Kilowatt-hour (kWh) | 3,600,000 J | UK electricity bills (Ofgem) |
| 1 Kilocalorie (kcal) | 4,184 J | Food / nutrition labelling |
| 1 BTU | 1,055.06 J | Boiler & HVAC ratings |
| 1 Megajoule (MJ) | 1,000,000 J | Natural gas billing (pence/MJ) |
| 1 Foot-pound (ft·lbf) | 1.35582 J | Impact energy, fasteners |
| 1 Electronvolt (eV) | 1.60218 × 10⁻¹⁹ J | Atomic / particle physics |
Common Energy Conversion Questions
How many joules are in a kilowatt-hour?
1 kWh = 3,600,000 joules (3.6 MJ). A kWh is the unit on UK electricity bills — the energy used by a 1,000 W appliance running for one hour. At approximately 24p/kWh (2024 Ofgem cap), that's 24 pence worth of electricity.
What is the difference between a calorie and a kilocalorie?
A calorie (cal, lowercase) = 4.184 J — the energy to heat 1 g of water by 1°C. A kilocalorie (kcal) = 1,000 calories = 4,184 J. Food "Calories" printed on UK packaging are kilocalories. So a 500 kcal meal = 500,000 cal = 2,092,000 J ≈ 0.581 Wh.
What is a BTU and how does it apply to UK boilers?
A BTU (British Thermal Unit) = 1,055.06 J. Boilers and air conditioning units are still often rated in BTU/hr. A typical UK combi boiler outputs 24,000–35,000 BTU/hr, which is 7–10 kW. When comparing boilers, divide the BTU/hr figure by 3,412 to get kW output.
How is natural gas billed in the UK?
UK gas meters measure volume (m³ or ft³). Suppliers convert this to kWh for billing by multiplying by the calorific value of gas (approximately 11.2 kWh/m³) and a conversion factor. Gas unit rates under the Ofgem cap are set in pence per kWh.
How many kWh does a typical UK household use?
Ofgem's typical domestic consumption figures: approximately 2,900 kWh/year electricity and 11,500 kWh/year gas for a medium home. This is what the energy price cap is calculated on. A larger detached house may use 4,000+ kWh electricity and 18,000+ kWh gas.