Battery Amp Hour Calculator
Calculate battery runtime from amp-hours and load, with a realistic depth-of-discharge limit.
Depth of discharge is not a detail
Lead-acid discharged past 50% repeatedly loses most of its cycle life; lithium iron phosphate tolerates 80–90%. A 100 Ah lead-acid battery is really a 50 Ah battery if you want it to last, which is how a lithium pack of half the nominal capacity can deliver more usable energy.
What this page needs from you
This page asks for battery capacity in Ah, load current in A and usable depth of discharge as a percentage. From those it returns runtime in h, together with usable capacity, energy at 12 v, runtime at half the load and charge time at 10 a. Every figure updates as you type, and nothing you enter leaves your browser.
Check the power rating, not just the value
Choosing a component by its resistance or capacitance alone leaves out the rating that actually determines whether it survives. Work out the power the part will dissipate and pick something rated for at least twice it: a resistor run at its limit gets hot enough to drift out of tolerance and to discolour the board.
The formula
Runtime = capacity × usable depth ÷ load current
Every result on this page comes from this formula. Nothing is rounded until the final display, so figures match a spreadsheet to the cent.
How to use the Battery Amp Hour Calculator
- Fill in each field with your own figures — the defaults are only there as an example.
- The result updates as you type, so there is no button to press.
- Check the breakdown under the main result for the supporting numbers.
- Use the copy button to take the result with you, or share the link to reload the same inputs.
Battery Amp Hour Calculator — frequently asked questions
Is this battery amp hour calculator free to use?
Yes. Every calculator on the site is free, needs no sign-up, and runs entirely in your browser, so your figures never leave your device.
How accurate is the result?
The maths is exact for the formula shown on the page. Accuracy in the real world depends on your inputs and on assumptions the formula cannot see, so treat the output as a well-grounded estimate rather than a quote.
Can I use it on my phone?
Yes. The page is responsive, weighs a few kilobytes and works offline once loaded, so it behaves the same on a phone as on a desktop.
What people search for
This page answers each of these searches. They are the exact phrases visitors use to find the battery amp hour calculator.
- battery amp hour calculator
- amp hours to hours
- how long will my battery run
- battery capacity calculator
- ah runtime calculator
About this calculator
Written and reviewed by The Samsung Calculator editorial team. Every calculator is written against a published formula, reviewed against at least one independent reference implementation, and dated when it changes.
Last reviewed September 14, 2026 · Calculation runs client-side · No data collected · Report an error