---
title: "kWh Cost Converter: kWh, MJ, Btu, Therms | Lightnest Market"
description: "Convert energy between kWh, Wh, MJ, Btu and therms, turn a price per kWh into a price per MJ or therm, and work out the cost of any amount."
url: https://lightnestmarket.shop/kwh-cost-converter/
---

# kWh cost converter

Electricity in kilowatt-hours, gas in therms or megajoules, a heater rated in Btu: put any of them on the same scale, with the price alongside.

Cost

$42.50

250 kWh at $0.17 per kWh

### That price is

Estimates from the figures you enter: not a bill, and not financial advice.

## Energy is energy, whatever the unit

Electricity is billed in kilowatt-hours, gas often in therms or megajoules, and heating equipment is rated in Btu. They all measure the same thing, so any amount converts exactly. One kilowatt-hour is 3.6 megajoules by definition; NIST gives one Btu as 1,055.056 joules and the U.S. therm as 105.4804 megajoules.

Prices convert the other way round: because a kWh is 3.6 MJ, a price per kWh is 3.6 times the price per MJ. That puts an electricity rate and a gas rate on the same footing, before you allow for how efficiently each appliance turns its fuel into heat.

1 kWh = 1,000 Wh = 3.6 MJ ≈ 3,412.14 Btu ≈ 0.0341 therm
Cost = energy in the price's unit × price

## Sources

- NIST, [NIST Guide to the SI, Appendix B.9](https://www.nist.gov/pml/special-publication-811/nist-guide-si-appendix-b-conversion-factors/nist-guide-si-appendix-b9): kilowatt hour = 3.6 MJ (exact); British thermal unit (IT) = 1.055 056 kJ; therm (U.S.) = 105.4804 MJ (exact); therm (EC) = 105.506 MJ.

## Questions

**Is a kWh the same as a kW?**

No. A kilowatt is a rate of use (power); a kilowatt-hour is an amount (energy), one kilowatt for one hour. A 2 kW heater running for 3 hours uses 6 kWh.

**Why compare gas and electricity prices per kWh?**

It shows what the energy itself costs. A gas boiler loses some heat up the flue, so divide a gas price by the boiler's efficiency before comparing it with an electric heater.

**Which therm does this use?**

The U.S. therm, 105.4804 MJ, as listed by NIST. The EC therm used in Europe is about 0.02% larger, too little to matter on a bill.