Joule Calculator
Convert joules, kWh, watt-hours, BTU, calories, and therms. Calculate energy from watts and time, estimate electricity cost, and solve Joule heating formulas.
Converted Value
J
In Joules
J
In kWh
kWh
Joule Conversion Reference
| Energy Unit | Joules | Use Case |
|---|---|---|
| 1 kWh | 3,600,000 J | A utility-bill energy unit. |
| 1 Wh | 3,600 J | One watt running for one hour. |
| 1 BTU IT | 1,055.055853 J | Common in heating and cooling specs. |
| 1 food Calorie | 4,184 J | One kilocalorie, often written Calorie. |
Core Joule Formulas
Watts to joules
J = W x seconds
A 100 W device running for 60 seconds uses 6,000 J.
Joules to kWh
kWh = J / 3,600,000
This is the bridge between physics energy and utility bills.
Electricity cost
Cost = kWh x rate
Use your actual utility rate for the most useful estimate.
Joule heating
J = I^2 x R x seconds
Useful for resistive heaters, wires, coils, and thermal load checks.
When to Use Joules vs kWh
Joules are the SI unit for energy, work, and heat. They are useful when you are working with short time spans, physics formulas, batteries, heaters, motors, and lab measurements. Kilowatt-hours are easier for home energy planning because utility bills charge for electricity in kWh.
That is why a useful joule calculator should not stop at a single conversion box. Many real problems need joules, watt-hours, kWh, and cost in the same workflow. This page keeps those conversions together so you do not have to jump between a unit converter and an electricity cost calculator.
Sources and Unit Notes
- NIST defines the joule as the preferred SI unit of heat, energy, or work.
- BIPM SI references list J as kg m^2 s^-2 and W as kg m^2 s^-3, which is why one watt equals one joule per second.
- EIA electricity guidance explains that utilities generally measure electricity in kilowatt-hours.
Next Energy Calculators
Frequently Asked Questions
How do you calculate joules from watts and time?
Multiply power in watts by time in seconds. A watt is one joule per second, so Energy (J) = Power (W) x Time (s). For example, 100 watts for 60 seconds equals 6,000 joules.
How many joules are in one kWh?
One kilowatt-hour equals 3,600,000 joules. That comes from 1,000 watts multiplied by 3,600 seconds in one hour.
How do I convert joules to electricity cost?
Convert joules to kWh by dividing by 3,600,000, then multiply by your electricity rate. Cost = Joules / 3,600,000 x price per kWh.
What is the Joule heating formula?
For electrical heating, energy can be estimated as E = V x I x t, or E = I^2 x R x t when current, resistance, and time are known. The answer is in joules when volts, amps, ohms, and seconds are used.