To calculate watts-hours from amp-hours, we need to use the following formula:

**Watt-hours = Amp-hours * Volts**

As we can see, amp-hours multiplied by voltage equals watt-hours.

Using this equation, we can accurately convert watt-hours from amp-hours. You can find the Ah to Wh calculator here:

We have also used the calculator to produce an amp-hour to watt-hour conversion chart for the most common Ah values (at 120V and 220V):

### Ah To Wh Conversion Chart

Amp-Hours (Wh) | Watt-Hours (at 120V): | Watt-Hours (at 220V): |
---|---|---|

0.1 amp hour to watt hours: | 12 Wh | 22 Wh |

0.2 amp hours to watt hours: | 24 Wh | 44 Wh |

0.3 amp hours to watt hours: | 36 Wh | 66 Wh |

0.4 amp hours to watt hours: | 48 Wh | 88 Wh |

0.5 amp hours to watt hours: | 60 Wh | 110 Wh |

1 amp hour to watt hours: | 120 Wh | 220 Wh |

2 amp hours to watt hours: | 240 Wh | 440 Wh |

5 amp hours to watt hours: | 600 Wh | 1100 Wh |

10 amp hours to watt hours: | 1200 Wh | 2200 Wh |

20 amp hours to watt hours: | 2400 Wh | 4400 Wh |

Knowing how to convert Ah to Wh is quite a useful trick. We have an interesting article about how long will a 100Ah battery last here with a 400W appliance example. Once you convert amp-hours into watt-hours, the calculation becomes much much easier.

I have a 300 amp hour LiFePo4 battery and the label on the side of the battery says that there are 3840 watt hours fully charged, I am guessing at 120V. In the chart above it says that 20 amp. hours equal 2400 watt hours at 120 V. If that is correct I don’t understnad why a 300 amp hour battery would not give 15 times that. (20 amp hours times 15 equals 300 amp hours) or 15 x 2400 watt hours, equalling 36,000 watt hours. Sorry for my confusion, please explain. Thanks, Jim

Hello Jim, here’s how you can figure this out: The 300 Ah battery contains 3,840 Wh when fully charged. That means that the voltage is 3,840Wh/300Ah = 12.8V. That’s a standard 12V battery voltage. You don’t have to guess the voltage, you can simply calculate it by dividing the watt-hours by amp-hours; the result is the voltage.

When you reduce that guessed 120V to 12V, you get the results in the chart. Hope this helps.

So hereâ€™s an example: If I have a 1.5kw solar panel, to 2 x 20 amp batteries – how long can I run a 300w heater (through a 220v inverter)?

Thanks

Hello Neil, here’s how you go about figuring that out: 300W heater requires 300W every hour to run (so that’s 300Wh). Now, two 2×20 amp batteries (they are probably 12V batteries) can produce 40A*12V = 480W. That means that the 300W heater will run for 480W/300W = 1.6 hours just on batteries.

If you can use the solar panels to continuously supply 1.5 kW of electricity to a 300W heater, it will easily run for as you as you’re capable to supply that power. Does this answer the question? Maybe you can specify a bit more and we can help you out further.