Energy Converter
Convert between joules, calories, kWh, BTU, therms and more. Then work out what an appliance actually costs to run with the built-in electricity calculator, in your own currency and rate.
Work out what an appliance actually costs to run, in your own currency and rate.
Enter your rate in whatever currency your bill uses — the calculator is currency-agnostic.
How to Convert an Energy Value
Features
150 Calories Is Actually 150,000
Every nutrition label runs on a small deception nobody questions. The "Calorie" printed on a snack wrapper — sometimes capitalised, usually not — is not the calorie chemistry class defined. A true small calorie is the energy needed to warm 1 gram of water by 1°C, about 4.184 J; the food "Calorie" is a kilocalorie, exactly 1,000 of those. So a bar of chocolate listed at 250 Calories is actually 250,000 of the small calories a lab would use — the label just quietly drops the "kilo." It's not a controversial fact once you know it, but it trips up anyone doing unit conversion by hand, which is exactly why this converter shows a direct warning the moment cal or kcal enters the picture instead of leaving the distinction to a footnote nobody reads. There is even a second, quieter version of the same problem for anyone working in a lab rather than a kitchen: the thermochemical calorie this tool uses (exactly 4.184 J) is very slightly smaller than the "International Table" calorie some steam-engineering and older combustion references use (4.1868 J) — a gap of about 0.07%, invisible for everyday purposes but occasionally worth checking on a precision engineering spec sheet.
33.7 Kilowatt-Hours in a Gallon of Gas
When the EPA needed a way to put an electric car's efficiency rating on the same sticker as a petrol car's miles-per-gallon, it worked out the actual chemical energy locked in a US gallon of gasoline and expressed it in electrical terms: 33.7 kWh, a figure introduced in 2010 and still the official conversion behind every MPGe rating on a modern EV window sticker. It's a statement about energy content, not about how far either vehicle actually travels on that energy — a combustion engine wastes the majority of that 33.7 kWh as heat before it ever reaches the wheels, while an electric motor keeps far more of its equivalent energy usefully in motion, which is a large part of why EVs post such favourable MPGe numbers despite starting from the same energy baseline. It also explains why an EV rated at a seemingly modest 100 MPGe is still using less real energy per mile than a petrol car rated at 40 MPG — the two ratings share a name and a shape, but the underlying physics behind them is not remotely equivalent.
A Kettle, an Air Conditioner, and a Silicon Chip
A 2,000 W kettle run for nine minutes uses almost exactly 0.3 kWh — a small enough amount that most people never think to convert it, right up until they're trying to work out why a monthly electricity bill looks the way it does. An American shopping for an air conditioner sees it rated at "12,000 BTU/h" and wants to compare that against a European unit specified in kilowatts — converted, that's roughly 3.5 kW, the kind of cross-market comparison that used to mean digging through a manufacturer's spec sheet footnotes. A semiconductor engineer, working at the opposite end of the scale entirely, checks that silicon's 1.12 eV band gap sits where expected relative to a competing material — a number so small it exists specifically because the joule is hopelessly oversized for describing single-electron energies — particle physicists working at the opposite end of that same scale casually describe collision energies at the Large Hadron Collider in TeV, a trillion electronvolts, rather than convert everything down to an almost meaninglessly small joule figure. And a homeowner reading a gas bill priced in therms converts it to the gigajoules a neighbour's European supplier uses, settling an argument about whose heating costs more per unit of actual energy delivered. A cyclist glancing at a bike computer that logs ride effort in kilojoules converts that figure to kilocalories to cross-check against a fitness app that only speaks the language of food energy, closing the loop between two devices that are, underneath, measuring exactly the same physical quantity.
Built to Answer "What Does This Cost?"
Most energy converters stop at a converted number. This one adds the question people actually have after that number appears: what does it cost to run? The Electricity Cost Calculator below the main converter accepts either an appliance's wattage and hours of use, or a kWh figure you already have, multiplies it against a rate you enter — in whatever currency your bill actually uses — and projects the cost out to a monthly and yearly estimate if that usage repeats daily. Next to the main result, a Real-World Reference panel does something similar for intuition rather than cost: it lists eight recognisable energy amounts, from a single AA battery up to a full day's output of a nuclear power plant, and highlights whichever one sits closest to your current figure so a number like "2.3 kWh" reads as roughly a day's food energy rather than an abstract quantity. Three filter chips above the full unit table — Metric & Food, Electrical, US & Scientific — keep a quick nutrition check from sharing space with electronvolts it has no use for. Precision follows the same pattern as the rest of the converter family: Auto keeps everyday figures short and readable, while a fixed 2, 4, 6, or 8 decimal-place setting is there for the moment an energy audit or a lab report needs one consistent format rather than whatever looks tidiest.
What This Meter Won't Show
This tool converts and totals energy — it does not model efficiency losses, so a kWh of electricity and a kWh-equivalent of gasoline are not interchangeable in terms of useful output once an engine or motor's conversion losses are accounted for. The Electricity Cost Calculator has no awareness of tiered pricing, time-of-use rates, standing charges, or taxes that many utilities layer on top of a simple per-kWh rate, so treat its output as a close estimate of the usage-based portion of a bill, not a guaranteed final figure. And energy is not power: a 2,000 W appliance describes a rate, not an amount, until you also know how long it ran — this tool handles that multiplication for you in the cost calculator, but it's worth knowing the distinction exists — confusing the two is common enough that it's worth a second look whenever a spec sheet or a bill uses the words loosely. Nothing typed here is sent anywhere: the arithmetic runs as plain JavaScript inside the browser tab, with no server call and nothing logged, which matters for a confidential energy audit or an unpublished dietary record as much as for checking a household bill, and the tool keeps working identically with no internet connection at all once the page has loaded. For anything with financial or regulatory weight behind it — a utility dispute, a commercial energy audit, a clinical dietary calculation — treat the output as a fast, accurate starting point and confirm the final figures against your actual bill or a qualified professional.