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. Below the calculator, you can also check an Ah to Wh conversion chart for 120V and 220V circuits, and the battery amps hours chart for 12V and 24V batteries.
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 (120V And 220V)
| 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 |
Batteries run on 12V or 24V voltage. Here is the full battery amps hours chart:
Battery Amps Hours Chart
| Battery Amp Hours (Ah) | Battery Watt Hours (At 12V) | Battery Watt Hours (At 24V) |
|---|---|---|
| 100 mAh | 1.2 Wh | 2.4 Wh |
| 1000 mAh or 1 Ah | 12 Wh | 24 Wh |
| 2 Ah | 24 Wh | 48 Wh |
| 3 Ah | 36 Wh | 72 Wh |
| 4 Ah | 48 Wh | 96 Wh |
| 5 Ah | 60 Wh | 120 Wh |
| 10 Ah | 120 Wh | 240 Wh |
| 20 Ah | 240 Wh | 480 Wh |
| 30 Ah | 360 Wh | 720 Wh |
| 40 Ah | 480 Wh | 960 Wh |
| 50 Ah | 600 Wh | 1200 Wh |
| 60 Ah | 720 Wh | 1440 Wh |
| 70 Ah | 840 Wh | 1680 Wh |
| 80 Ah | 960 Wh | 1920 Wh |
| 90 Ah | 1080 Wh | 2160 Wh |
| 100 Ah | 1200 Wh | 2400 Wh |
| 120 Ah | 1440 Wh | 2880 Wh |
| 140 Ah | 1680 Wh | 3360 Wh |
| 160 Ah | 1920 Wh | 3840 Wh |
| 180 Ah | 2160 Wh | 4320 Wh |
| 200 Ah | 2400 Wh | 4800 Wh |
| 250 Ah | 3000 Wh | 6000 Wh |
| 300 Ah | 3600 Wh | 7200 Wh |
| 350 Ah | 4200 Wh | 8400 Wh |
| 400 Ah | 4800 Wh | 9600 Wh |
| 450 Ah | 5400 Wh | 10800 Wh |
| 500 Ah | 6000 Wh | 12000 Wh |
| 600 Ah | 7200 Wh | 14400 Wh |
| 700 Ah | 8400 Wh | 16800 Wh |
| 800 Ah | 9600 Wh | 19200 Wh |
| 900 Ah | 10800 Wh | 21600 Wh |
| 1000 Ah | 12000 Wh | 24000 Wh |
| 2000 Ah | 24000 Wh | 48000 Wh |
Example: Let’s say you have a 100 Ah battery running on 12V. What is the battery capacity in Wh? You can just consult this battery amp hours chart and see that a 100 Ah battery has a 1200 Wh battery capacity.
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 here’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.
Can someone help me with the calculations on this please. I have a 12V 41ah car battery. This goes to an alternator which then outputs 220v-240v to a device which uses 1500w. How long would this device last running off the fully charged battery?
Hello George, of course. First, you calculate the capacity of the battery in Wh; 12V*41Ah = 492 Wh. Now, this capacity can run a 492W device for 1 hour. If you have a 1,500W device, you do this calculation: 492Wh/1,500W = 0.328 h or about 20 minutes. This is how long a fully charged 12V 41Ah car battery can sustain 1,500W output. Hope this helps.
Hi George. I have a led acid 12v 200ah tubular battery. Running a embroidery mechine 300 watt how long can I run this mechine with this battery off an inverter
Hi there, you might find this helpful: 12V × 200Ah = 2,400 Wh. This can run a 300W device for 8 hours.
Please help me I can’t until any of this. I bought a solar panel kit. Panels are 100wh each to two 12v/ 20AH batteries connected to a 600 wh solar inverter. I plugged a space heater into the inverter and it could not power but I was told this setup could power my travel trailer.
Hello Kathryn, space heaters usually run on 1,500W. The setup with 100W panels and 600Wh solar inverter might be a bit too small to run a 1,500W device. You could try running the heater on the lowest possible setting and see if that works.
I have a fordexpition 2002 comper and I was trying run a 840watts A/c but works for few minutes the than the battery gets low the alternator is charging good and the battery is good
are-lifepo4-battery-any-good
Sure, Greg, these are the best batteries we have. Even Tesla uses them.
i just want my fridge to work for 12 hours a day..what do i need? how many solar panels, how big the inverter..what else i need..i have the sun..live in P.R…..please heeeelp…i cannot deal with all those numbers..just tell me what do i need to buy. thank you…
Hello Danielle, sadly there is no one-size-fits-all answer here. An average fridge runs from 1 kWh to 2 kWh per day. If you want to use it for 12 hours per day, it will require at most 1 kWh. If you are using 100W solar panels in a location with 5 peak hours, one such panel will generate 0.5 kWh per day. To run your fridge on 100W solar panels, you would need 2 of these smaller panels. 1 300W panel should do the job as well. Hope this helps.
I have a backup power device with a capacity of 2016Wh 50.4v, if I plug a load of 6 Amps at 120v, for how long will it last?
Thank you
Hello Hernan, alright, we have a backup capacity of 2,016 Wh, and 6A*120V = 720W load. Here is how you can calculate this: 2,016Wh/720W = 2.8h. Basically, your backup power device will last 2 hours and 48 minutes when powering a 720W device. Hope this helps.
Ok It looks like I found a site that can help me…Sweet!
I have (6) 2VDC (UPS DEEP CELL) 165 Ah batteries wired in series to a12vdc string.
I have (4) of those 12vdc strings wired in series-parallel to 48vdc.
is my capacity doubled
My calcs say I have (4) 165ah battery strings to 48vdc. 4 x165= 640Ah.
Is this correct?
Below does not consider only 50% max depletion of batteries
my run time for simplicity if at 640Ahs 10amps @ 48vdc= 64hours run time.
Need help My Brain hurts…LOL
Hello Stan, the calculations are the theoretical estimates, yes. As you have correctly suggested, you have to factor in the losses that are specific to different batteries (lead batteries may have max depletion of 50%).
Stan,
You have 6 – 2volt 165ah batteries wired to 12v correct? That’s wired in series. Your at 12v 165ah.
Now you have 4 – 12v 165ah batteries wired to 48v correct? That is also wired in series. Your at 48v 165ah battery bank
Series wiring you add the voltage
Parallel wiring you add the amps
According to your explanation, everything is wired in series.
End result is 48v 165ah.
Hello I have a 12v 150 CCA lead acid battery how long would it power a trolling motor that uses 30wh
Hello Charlie, a 12V 150Ah battery has a 1,800Wh capacity. That would theoretically mean it can run a 30 Wh trolling motor for 60 hours. However, CCA lead acid batteries usually have a discharge rate of about 50%. Practically that means you will be able to run a 30Wh motor for about 30 hours. Hope this helps.
Hi, (hopefully this makes sense)
I have a 130ah lead acid battery,
I want to use two 100 watt devices, through a 300 watt inverter or a 12v to 24v step up \ booster depending which is more efficient???
How long could one expect the battery to last?
Thanks for any help 🙂
Hi Cory, alright, the 130 Ah lead acid battery (presuming it is a 12V battery) has a 1560 Wh capacity. The two devices have a combined power draw of 200W. Theoretically, this battery could run the devices for 1560Wh / 200W = 7.8 hours if the discharge rate of the battery would be 100%. In the case of lead acid batteries, the discharge rate is about 50%. So you will be able to run these two devices for 3.9 hours (about 4 hours). Hope this helps.
I have Milwaukee M18 Topoff 175 watt inverter that runs off a 12.0ah 18v battery. I’m wondering how long can run 120v 45 watts food warmer? Thanks
Hi Daniel, if we presume a 100% discharge rate, the 12.0Ah 18V battery has a 216 Wh capacity. If you want to run a 45W food warmer, you can divide the capacity by the wattage like this: 216Wh / 45W = 4.8h. That’s 4 hours and 48 minutes run time. Hope this helps.
Hello! I have a window unit that I want to buy but I’m going to have to have a solar setup first. I understand that this setup with be expensive. It’s a 15,000 btu unit! Here are some specifics, and maybe you guys can tell me what my solar system needs to look like.
115 volts
11.8 amps
1260 watts
Hi Josh, it seems like you have window AC unit with high energy efficiency (11.9 EER rating) which is great. Alright, let’s assume that you want to use the window AC unit for 8 hours per day and use the SEER average output of 58%.
That means that the unit is running, on average, at 731W. In 8 hours, it will use 5.848 kWh (we can say 6 kWh per day, just to be safe).
You would need a solar system that can generate 6 kWh per day. Now, let’s assume that at your location you get an average of 5 peak sun hours per day. A 1000W solar system would produce 5 kWh per day; add about 25% losses in there, are you are at 3.75 kWh per day. So, the 1000W solar system would be too small.
1.5kW solar system would (same math) produce 5.63 kWh per day; this might just be enough, especially if you live in a sunny state like California or Texas. To be sure the set up will work, you should go for 2k solar system that will produce 7.5 kWh per day. That will run a 15,000 BTU window AC and you can store the overflow electricity in a battery for cloudy days. Hope this helps.
Hello! Greetings! I have 4 12V 280Ah batteries. How many kwh will they give fully charged and how many solar panels I will need. I know I have to convert them to 48V.
Hi Luis, alright, you can calculate the total capacity like this: 4 x 12V x 280Ah = 13,440Wh or 13.44 kWh.
Number of solar panels: If you get 5 peak sun hours per day at your location, apply the 25% losses, you would need about 3,500W system. If you use standard 400W panels, you would neeed about 8 400W panels. Hope this helps.