Energy

Multiply by 3,600,000: kWh × 3,600,000 = J. Example: 1 kWh = 3,600,000 J = 3.6 MJ. The factor comes from: 1 kW = 1,000 W = 1,000 J/s; 1 hour = 3,600 s; so 1 kWh = 1,000 × 3,600 = 3,600,000 J. Reverse: J ÷ 3,600,000 = kWh. Example: a 60 W bulb running for 10 hours uses 60 × 36,000 = 2,160,000 J = 0.6 kWh. The kWh is not an SI unit, but it is the global billing standard because kilowatts and hours are far more intuitive than megajoules for household energy consumption.

Multiply by 4.184: kcal × 4.184 = kJ. Example: 500 kcal = 2,092 kJ. Reverse: kJ ÷ 4.184 = kcal. Example: 100 kJ = 23.9 kcal. Important distinction: 1 food Calorie (Cal) = 1 kilocalorie (kcal) = 1,000 small calories (cal). The small calorie (4.184 J) is the heat needed to raise 1 g of water by 1 °C; the food Calorie is 1,000× that. When a nutrition label says "250 Calories," it means 250 kcal = 1,046 kJ. Australia and the EU increasingly mandate kJ on food labels alongside kcal.

Btu (IT) to joules: Btu × 1,055.06 = J. Example: 1,000 Btu = 1,055,060 J ≈ 1.055 MJ. Btu to kWh: Btu × 0.000293071 = kWh. Example: 1 Btu = 0.000293 kWh. The two Btu variants differ slightly: IT (International Table) Btu = 1,055.056 J; thermochemical Btu (th) = 1,054.35 J. The difference is ~0.07% — negligible for building energy but matters in precision thermodynamic calculations. For HVAC: a 12,000 Btu/hr air conditioner = 12,000 × 1,055.06 / 3,600 = 3,517 W ≈ 3.5 kW.

Three steps: (1) Type any energy value — integers and decimals accepted (e.g., 3.6 MJ, 1000 kcal, 29.92 Btu, 500 eV, 1.5 kton). (2) Select the source unit from the full dropdown: joule, kJ, MJ, GJ, kWh, MWh, GWh, Wh, W·s, N·m, kcal, Btu (IT), Btu (th), hp·h, ton/kiloton/megaton/gigaton TNT, eV, keV, MeV, and all millijoule–attojoule SI variants. (3) All units update instantly. Tap Copy beside any row. Free at untangletools.com/unit/category/energy — no login required.

Yes: kWh × 3.6 = MJ and MJ ÷ 3.6 = kWh. Example: 10 kWh = 36 MJ. Both measure the same quantity — they just originate from different traditions. kWh comes from electrical engineering (power × time in practical units); MJ is pure SI. Gas bills in Australia use MJ; UK gas bills use kWh; US gas bills use Btu or therms. Energy auditors, building physicists, and carbon accountants routinely work across all three — the converter outputs all simultaneously from one input.

Electricity meters measure kilowatt-hours (kWh) — the energy consumed by a 1,000 W (1 kW) device running for one hour. Scale relationships: 1 MWh = 1,000 kWh (large industrial facility for a day); 1 GWh = 1,000 MWh = 1,000,000 kWh (a small power plant's daily output). A typical household kWh price in the UK is ~28p; in the US ~$0.16. Annual household consumption: UK ~3,500 kWh ≈ 12.6 GJ; US ~10,500 kWh ≈ 37.8 GJ. Energy storage projects (like the Hornsdale Power Reserve, 150 MWh) use MWh; national generation statistics use GWh or TWh (terawatt-hours, 10⁶ MWh).

Fission of one uranium-235 atom releases approximately 200 MeV = 3.2×10⁻¹¹ J. Per gram of U-235: ~82 TJ = 82,000 GJ. By comparison, 1 gram of TNT releases ~4,184 J. The ratio: U-235 is roughly 20 million times more energy-dense than TNT. This is why the Hiroshima bomb (~64 kg U-235, ~15 kt yield = 6.3×10¹³ J) had such destructive power from a relatively small mass. Nuclear reactor fuel: a single fuel rod (~0.5 kg UO₂ enriched to 3–5%) generates ~43,000 kWh of electricity — enough for a UK home for 12+ years from a rod the size of a finger.

A watt-second (W·s) is dimensionally identical to a joule — 1 W·s = 1 J exactly, because 1 W = 1 J/s and 1 J = 1 W × 1 s. They appear as separate units in converter tools because different engineering contexts favour one notation over the other. Flash photography uses W·s (also called "joule" in strobe specs): a studio flash rated at 500 W·s releases 500 J per flash. Capacitor energy storage is expressed in joules but derived from W·s in power electronics. The N·m (newton-metre) is similarly equal to 1 J when used as an energy unit — though N·m also describes torque, which is a different physical quantity despite identical dimensions.

Modern particle colliders operate at TeV (teraelectron-volt) energies. 1 TeV = 10¹² eV = 1.602×10⁻⁷ J. The Large Hadron Collider (LHC) at CERN collides protons at 13–14 TeV centre-of-mass energy — roughly equal to the kinetic energy of a flying mosquito (10⁻⁶ J) concentrated into a single proton. This is why high-energy physics requires eV notation: 1 TeV per proton = 1.602×10⁻⁷ J — a value that would be useless to express in joules for day-to-day accelerator physics. The Higgs boson mass is 125 GeV/c²; a top quark is 173 GeV/c². Converting these to joules (via E = mc²) gives values in femtojoules — technically correct but practically unusable in calculations.