Energy Converter — Calculator

About energy conversions

Energy is power multiplied by time, so a watt-hour is one watt sustained for one hour. The joule is the SI unit, and 3.6 megajoules make one kilowatt-hour — the unit on an electricity bill and the 'unit' on a prepaid meter.

Food and heating use older units. A kilocalorie is 4,184 joules and is the 'calorie' printed on food labels; a BTU is 1,055.05585262 joules and is the heating and cooling unit in imperial countries. All four are defined against the joule, so every conversion here is exact arithmetic.

Electricity bills and prepaid meter units (kilowatt-hours).
Battery and power-bank capacity (watt-hours).
Food energy (kilocalories or kilojoules).
Heating and cooling capacity (BTU).

Reading the answers. All factors are exact definitions, so only the display is rounded.

The units in this converter

What each unit is and where it is normally used. Everything here is converted through the joules.

Joules (J): The joule is the SI unit of energy: the work done by one newton over one meter. It is used for small energy amounts in physics and engineering.
Kilojoules (kJ): A kilojoule is 1,000 joules. It is used for food energy in most countries outside the United States, and for small industrial figures.
Megajoules (MJ): A megajoule is 1,000 kilojoules, or about 0.278 kilowatt-hours. It is used for the energy content of fuels: a litre of diesel holds roughly 36 megajoules.
Watt-hours (Wh): A watt-hour is the energy of one watt sustained for one hour — 3,600 joules. It is used for battery and power-bank capacity; a phone battery is typically 10 to 20 watt-hours.
Kilowatt-hours (kWh): A kilowatt-hour is 1,000 watt-hours, or 3.6 megajoules. It is the unit on electricity bills, and the 'unit' shown on a prepaid meter.
Calories (cal): A calorie here is the small calorie of 4.184 joules — the energy needed to raise one gram of water by one degree Celsius. Food labels use the kilocalorie, which is 1,000 of these.
Kilocalories (kcal): A kilocalorie is 1,000 calories, or 4,184 joules. It is the 'calorie' on food labels, so a 2,000-calorie diet means 2,000 kilocalories.
BTU (BTU): A BTU (British thermal unit) is 1,055.05585262 joules — the energy needed to heat one pound of water by one degree Fahrenheit. It is used for heating and cooling capacity.

Tanzania reference points

Real quantities in energy, shown in the units people actually use.

One unit of electricity on a Tanzanian prepaid meter
1 kWh · 3,600,000 J · 3,600 kJ · 3.6 MJ · 1,000 Wh · 860,420.650096 cal · 860.42065 kcal · 3,412.141633 BTU
The average domestic rate was about 229.59 TZS per kWh as of December 2025, including taxes and supply. That is an average across domestic customers, not the marginal rate on a bill.
Source: GlobalPetrolPrices — Tanzania electricity prices (compiled from EWURA/TANESCO tariffs) · verified 2026-09-14

Popular conversions

Kilocalories to Kilojoules Kilojoules to Kilocalories Kilowatt-hours to Joules Joules to Kilowatt-hours Kilowatt-hours to Megajoules Calories to Kilojoules

Convert from any energy unit

Each unit has its own page with every other unit in the dimension, the exact factor for each, and worked values.

Joules converterJ to 7 other energy units Kilojoules converterkJ to 7 other energy units Megajoules converterMJ to 7 other energy units Watt-hours converterWh to 7 other energy units Kilowatt-hours converterkWh to 7 other energy units Calories convertercal to 7 other energy units Kilocalories converterkcal to 7 other energy units BTU converterBTU to 7 other energy units

Frequently asked questions

How many joules are in a calorie?

One calorie equals 4.184 joules, and one food Calorie (kilocalorie) equals 4,184 joules.

How many joules are in a kilowatt-hour?

One kilowatt-hour equals 3.6 million joules.

What is a BTU?

A British Thermal Unit is the energy needed to heat one pound of water by 1°F; it equals about 1,055 joules.

All energy conversions

Every energy conversion on Calculator, listed in full.