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.

An electron-volt (eV) is the kinetic energy gained by an electron when accelerated through a potential difference of exactly 1 volt. 1 eV = 1.602176634 × 10⁻¹⁹ J (exact, by SI definition since 2019). keV to J: multiply by 1.602×10⁻¹⁶. MeV to J: multiply by 1.602×10⁻¹³. Practical scale: a photon of visible light carries ~2–3 eV; X-ray photons carry 0.1–100 keV; the Hiroshima bomb released energy equivalent to about 6.3×10¹³ J = 3.94×10³² eV. The eV persists in particle physics because 1 eV is a natural, human-scale energy at the atomic level — whereas 1.6×10⁻¹⁹ J requires constant scientific notation.

1 ton of TNT = 4,184,000,000 J = 4.184 GJ exactly (defined, not measured). Kiloton to joules: kton × 4.184×10¹² = J. Example: 1 kiloton TNT = 4.184 TJ (terajoules). Megaton to joules: 1 Mton = 4.184 × 10¹⁵ J. Context: the Hiroshima bomb yielded ~15 kilotons = 62.76 TJ; the largest nuclear test ever (Tsar Bomba, 1961) yielded 50 megatons = 209,200 TJ = 2.09×10¹⁷ J. The TNT-equivalent system exists to make explosive/nuclear energy comprehensible — otherwise comparing a grenade (few MJ) to a thermonuclear weapon (10¹⁷ J) requires 10 orders of magnitude mental arithmetic.

The small calorie (cal) = 4.184 J — the energy to heat 1 gram of water by 1 °C. The kilocalorie (kcal) = 1,000 cal = 4,184 J — used in nutrition and chemistry. The capital-C Calorie (Cal) on US food labels = 1 kcal = 4,184 J — the same as kcal, confusingly capitalised. The joule (J) is the SI unit — 1 J = 0.239 cal = 0.000239 kcal. Engineers and scientists use joules; nutritionists use kcal; the gap causes persistent confusion in fitness apps, diet studies, and food policy when kJ and kcal are mixed on the same label.

1 MJ = 1,000,000 J = 1,000 kJ = 0.2778 kWh = 239 kcal. Real-world context: 1 MJ will heat 239 mL of water from 0 °C to 100 °C; power a 100 W light bulb for 2.78 hours; propel a 1,000 kg car at 100 km/h for about 2.4 seconds (kinetic energy only); or equal the food energy in one modest meal (~240 kcal). A litre of diesel holds about 36–38 MJ; a litre of petrol ~34 MJ; a litre of liquid hydrogen ~10 MJ. These benchmarks make MJ the most intuitive unit for comparing energy densities across different fuels.

Metric horsepower hour to joules: hp·h × 2,647,796 = J. Example: 1 hp·h = 2.648 MJ = 0.7355 kWh. Mechanical (US) horsepower hour: hp·h × 2,685,000 = J ≈ 2.685 MJ = 0.746 kWh. The metric and US values differ because 1 metric hp = 735.5 W vs 1 US hp = 745.7 W. Horsepower-hours appear in older engine specifications and industrial equipment ratings — a diesel generator running at 100 hp for 8 hours produces 800 hp·h = 2,118 MJ ≈ 588 kWh of mechanical output (before accounting for thermal efficiency).

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.

Yes — the full SI joule prefix family is supported: millijoule (mJ), microjoule (μJ), nanojoule (nJ), and attojoule (aJ). These appear in: mJ — laser pulse energies, explosive primer charges; μJ — MEMS actuators, neural stimulation pulses; nJ — optical fibre signal levels, photon detection thresholds; aJ — single chemical bond energies (~0.1–10 aJ), thermal noise energy kT at room temperature (≈ 4 aJ). The converter handles 64-bit floating-point throughout — no precision loss entering values like 1.602×10⁻¹⁹ for 1 eV.

Yes. All factors use exact or CODATA-defined values: 1 kWh = 3,600,000 J (exact); 1 kcal = 4,184 J (exact, IT definition); 1 Btu (IT) = 1,055.05585262 J (exact, ISO 31-4); 1 eV = 1.602176634×10⁻¹⁹ J (exact, 2019 SI redefinition); 1 ton TNT = 4.184×10⁹ J (exact, NIST). Completely free at untangletools.com/unit/category/energy — no account, no subscription, no ads during conversion.

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).

Energy density by volume: Petrol (gasoline) ≈ 34.2 MJ/L = 9.5 kWh/L; Diesel ≈ 38.6 MJ/L = 10.7 kWh/L; Liquid natural gas (LNG) ≈ 22.2 MJ/L; Ethanol ≈ 23.5 MJ/L; Hydrogen (700 bar) ≈ 4.7 MJ/L; Lithium-ion battery ≈ 0.9–1.8 MJ/L. This is why battery electric vehicles need large packs (~50–100 kWh = 180–360 MJ) to match the range of a ~50 L petrol tank (≈ 1,710 MJ of chemical energy) — even accounting for the EV drivetrain's ~3× efficiency advantage over an ICE engine (~25% thermal efficiency vs ~90% motor efficiency).

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.

Both are correct — they're just different units for the same energy. European Union law requires food labels to display energy in kJ first, then kcal in brackets (e.g., "837 kJ / 200 kcal"). United States FDA labels use "Calories" (capital C = kcal) without kJ. Australia and New Zealand require kJ, with kcal optional. 1 kcal = 4.184 kJ exactly. The confusion arises because biochemists use kcal in thermodynamic tables, dietitians count Calories (= kcal), and physicists prefer kJ or joules — all describing identical food energy. The trend toward kJ-only labelling reflects the global shift to SI units in public health policy.

1 gigaton of TNT = 4.184 × 10¹⁸ J — equivalent to the annual output of ~33,000 nuclear power plants, or roughly 1/14,000th of the energy Earth receives from the Sun per year. This scale is relevant in: (1) Asteroid impacts — the Chicxulub impactor (KT extinction, 66 Ma) released ~100,000 Gton TNT = 4.184×10²³ J; (2) Plate tectonic energy — the 2004 Indian Ocean earthquake released ~25 Gton TNT; (3) Climate energy budget — total human greenhouse gas warming adds ~4 Hiroshima bombs' worth of energy to Earth's system every second. These comparisons require the gigaton scale to be comprehensible.

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.