CalcaTools

Joules Converter | Convert Energy Between Joules and Common Units

Convert energy between joules, kilojoules, calories, kilocalories, watt-hours, kilowatt-hours, BTU, foot-pounds and electronvolts, with the exact conversion factors applied. Understand the calorie-versus-Calorie distinction and translate energy figures across physics, nutrition and engineering.

Last updated: July 2026 · Free · No sign-up required

Results

Enter values above and click Calculate to see your result instantly.

Quick reference

UnitIn joules
1 calorie (thermochemical)4.184 J
1 kilocalorie (food Calorie)4,184 J
1 BTU1,055.06 J
1 watt-hour3,600 J
1 kilowatt-hour3,600,000 J
1 foot-pound1.3558 J

info Joules Converter

Free converters calculator — enter your numbers and get an instant, accurate result.

info Private by design

Everything runs locally in your browser. No uploads, no accounts, no tracking.

info Works everywhere

Fully responsive and mobile-friendly — calculate on any device, any time.

info Educational

Includes the formula and step-by-step explanation so you understand the math, not just the answer.

Interpretation guide

EnergyRoughly equals
100 JLifting 10 kg about 1 meter
4,184 J (1 kcal)One food Calorie on a nutrition label
1 MJAbout 0.28 kWh — 17 minutes of a 1 kW heater
3.6 MJ (1 kWh)One unit on your electricity bill

lightbulb Worked example

Let's say you are using the Joules Converter. Converts any energy value between joules, kJ, calories, kcal, Wh, kWh, BTU, foot-pounds and electronvolts. Enter the values that match your situation into the input fields and press calculate — using realistic numbers makes the result directly useful for you.

Result: The calculator instantly applies the formula Value in joules = input × unit factor; output = joules ÷ target factor (1 cal = 4.184 J, 1 BTU = 1055.06 J, 1 kWh = 3.6×10⁶ J) and returns the result with appropriate precision.

What this means: Read the result in the context of what you are measuring. The step-by-step breakdown lets you confirm the math and understand which input most affects the outcome.

Formula & methodology

Formula: Value in joules = input × unit factor; output = joules ÷ target factor (1 cal = 4.184 J, 1 BTU = 1055.06 J, 1 kWh = 3.6×10⁶ J)

The Joules Converter is built on a well-established calculation method. It uses the formula Value in joules = input × unit factor; output = joules ÷ target factor (1 cal = 4.184 J, 1 BTU = 1055.06 J, 1 kWh = 3.6×10⁶ J) to turn your inputs into a reliable result. Converts any energy value between joules, kJ, calories, kcal, Wh, kWh, BTU, foot-pounds and electronvolts. The steps are shown on the page so you can follow the reasoning from input to output.

  1. Your input is first converted to joules using exact SI factors.
  2. The joule value is then divided by each target unit's factor.

Worked example: 1,000 J = 0.239 kcal = 0.948 BTU = 737.56 ft⋅lb = 0.000278 kWh. Going the other way, 500 food Calories (kcal) = 2,092 kJ — the energy in a typical fast-food burger.

Authoritative source: U.S. National Institute of Standards and Technology

Frequently asked questions

How do I convert joules to calories?
Enter the required values into the input fields and press the calculate button. The tool applies the formula Value in joules = input × unit factor; output = joules ÷ target factor (1 cal = 4.184 J, 1 BTU = 1055.06 J, 1 kWh = 3.6×10⁶ J) and returns the result with a short explanation of each step, so you can check the working yourself.
How many joules are in a kWh?
The Joules Converter is free, private, and accurate: it runs entirely in your browser (no uploads, no accounts), applies the standard calculation, and explains each step so you can verify the result. Converts any energy value between joules, kJ, calories, kcal, Wh, kWh, BTU, foot-pounds and electronvolts. There is no limit on usage, and it works on any device.
What is the difference between a calorie and a Calorie?
A lowercase calorie (cal) is 4.184 joules — the energy to raise 1 gram of water by 1°C. A capital Calorie (Cal) is a kilocalorie (1,000 cal = 4,184 J), the unit used on food labels. The converter distinguishes them: 'calories' on food packaging are actually kcal. Getting the case right matters by a factor of 1,000.
How do I convert joules to BTU?
Divide by the exact factor: 1 BTU = 1,055.06 joules, so joules ÷ 1,055.06 = BTU. For example, 10,000 J ≈ 9.48 BTU. The converter handles all pairs — joules, kJ, calories, kcal, Wh, kWh, BTU, foot-pounds, and electronvolts — by converting the input to joules first, then to the target unit.
What is an electronvolt?
An electronvolt (eV) is the energy an electron gains moving through a potential difference of one volt: 1 eV ≈ 1.602 × 10⁻¹⁹ joules. It is the natural energy unit for atomic and particle physics, which is why you see keV and MeV in physics while engineering uses joules. The converter bridges the two scales, with 1 J ≈ 6.24 × 10¹⁸ eV.
How do I calculate energy in joules from mass and velocity?
Kinetic energy: E = ½mv² with mass in kg and velocity in m/s. A 0.145 kg baseball at 40 m/s carries ½ × 0.145 × 1600 = 116 J. Once you have joules, this converter moves the result into calories, watt-hours, ft·lb, or BTU — 116 J is about 27.7 calories or 85.6 ft·lb.
What does the Joules Converter do?
Converts any energy value between joules, kJ, calories, kcal, Wh, kWh, BTU, foot-pounds and electronvolts. The calculator takes your inputs, applies the standard calculation, and returns a clear result so you can make an informed decision without doing the math by hand.
What formula does the Joules Converter use?
The Joules Converter applies the standard formula: Value in joules = input × unit factor; output = joules ÷ target factor (1 cal = 4.184 J, 1 BTU = 1055.06 J, 1 kWh = 3.6×10⁶ J). The tool walks through each step of the calculation so you can verify the numbers yourself.
Is the Joules Converter free and private?
Yes — the Joules Converter. There is no sign-up, no paywall, no trial, and no limit on how many calculations you can run. CalcaTools covers its costs with non-intrusive display advertising, so the calculator itself never asks for payment or restricts any feature.
How accurate is the Joules Converter?
The Joules Converter applies the standard formula: Value in joules = input × unit factor; output = joules ÷ target factor (1 cal = 4.184 J, 1 BTU = 1055.06 J, 1 kWh = 3.6×10⁶ J). It is tested against published worked examples before launch and uses native double-precision arithmetic, so results are accurate to typical precision for the values you enter — with no intermediate rounding that could distort the answer.

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