How do I convert mAh to Ah?

Divide the milliamp-hours by 1,000. A 5,000mAh battery is 5Ah. A 20,000mAh power bank is 20Ah. The "milli" prefix means one-thousandth. Manufacturers of small batteries and power banks use mAh because the number looks larger — "20,000mAh" sounds more impressive than "20Ah," even though they are identical.

Why do some batteries list Wh instead of Ah?

Watt-hours is a more complete measure of energy because it accounts for voltage. Airlines require lithium batteries to be labeled in Wh for safety regulations (the carry-on limit is 100Wh without airline approval ). Some manufacturers also prefer Wh because it makes cross-voltage comparisons easier. A 500Wh battery stores the same energy regardless of whether it is a 12V, 24V, or 48V system.

Is a 100Ah 12V battery the same as a 200Ah 6V battery?

They store the same total energy — both equal 1,200Wh (100 x 12 = 1,200; 200 x 6 = 1,200). But you cannot substitute one for the other without rewiring. Devices designed for 12V will not work on 6V. To use a 6V battery in a 12V system, you need two 6V batteries wired in series, which gives you 12V at the lower amp-hour rating (200Ah stays 200Ah, but at 12V — so 2,400Wh total for the pair). To figure out how many amp-hours your appliances actually need, the electrical load calculator totals daily consumption in watt-hours.

How many amp-hours do I need to run a 1,000-watt appliance for one hour?

Start with the energy: 1,000 watts for one hour is 1,000 watt-hours. Divide by your battery voltage for raw amp-hours: 1,000Wh / 12V is about 83Ah. But you cannot use every amp-hour, so allow for depth of discharge (about 50% for lead-acid, 80% for LiFePO4) and roughly 85% inverter efficiency for AC loads. After those losses you need about 195Ah of lead-acid, or 122Ah of LiFePO4, at 12V to cover that single hour.

Does temperature change a battery's amp-hour capacity?

Yes. Amp-hour ratings are measured at room temperature, around 20 to 27°C (68 to 80°F), and capacity falls as the battery gets colder. Battery University reports that a cell delivering 100% of its rated capacity at 27°C typically gives only about 50% at -18°C (0°F). The good news is that the loss is temporary and returns once the battery warms back up to room temperature. Heat does not cut capacity in the short term, but sustained high temperatures shorten the battery's overall life.

Battery Amp Hours Calculator — Wh, V & C-Rate Math

6 min read

Amp-hours = watt-hours ÷ volts (Ah = Wh ÷ V). Battery capacity appears in different units on different labels — amp-hours (Ah), watt-hours (Wh), or sometimes milliamp-hours (mAh). Converting between them requires knowing the voltage. This calculator turns watt-hours into amp-hours so you can compare batteries rated in different units on equal footing.

Battery capacity conversion from watt hours to amp hours by dividing by voltage.

How to Read Your Battery Label

Find the capacity rating. Look for "Ah" (amp-hours), "Wh" (watt-hours), or "mAh" (milliamp-hours) on the label. Larger batteries usually list Ah. Power banks and laptops list mAh or Wh.
Find the voltage. Look for "V" (volts) — this is the nominal voltage. A "12V" battery actually operates between 10.5V (empty) and 14.4V (charging), but 12V is the nominal used for calculations. LiFePO4 "12V" batteries are actually 12.8V nominal.
Convert if needed. Ah to Wh: multiply Ah by voltage. Wh to Ah: divide Wh by voltage. mAh to Ah: divide by 1,000. Examples: 100Ah at 12V = 1,200Wh. 20,000mAh at 3.7V = 74Wh = 20Ah.
Compare fairly. A 50Ah 24V battery stores the same energy as a 100Ah 12V battery — both are 1,200Wh. Always convert to watt-hours for apples-to-apples comparison across different voltages.

Amp hours formula breakdown: Ah equals Wh divided by V with labeled variables. — Converting between Wh and Ah requires only the battery voltage — 1,200 Wh at 12V = 100 Ah, but the same 1,200 Wh at 24V = only 50 Ah.

Quick Amp-Hour Conversion Table

Watt-Hours	At 2V (Ah)	At 6V (Ah)	At 12V (Ah)	At 24V (Ah)	At 48V (Ah)
600 Wh	300 Ah	100 Ah	50 Ah	25 Ah	12.5 Ah
1,200 Wh	600 Ah	200 Ah	100 Ah	50 Ah	25 Ah
2,400 Wh	1,200 Ah	400 Ah	200 Ah	100 Ah	50 Ah
4,800 Wh	2,400 Ah	800 Ah	400 Ah	200 Ah	100 Ah
9,600 Wh	4,800 Ah	1,600 Ah	800 Ah	400 Ah	200 Ah
14,400 Wh	7,200 Ah	2,400 Ah	1,200 Ah	600 Ah	300 Ah

The pattern holds across the range: doubling the voltage halves the amp-hours for the same energy. That is why 2V cells show up in large stationary and forklift banks, 6V cells in golf-cart and RV setups, and 48V in whole-home systems. Higher voltage carries the same power at lower current, which means thinner, cheaper cables.

Combining batteries shifts the totals in a predictable way. Wiring two identical batteries in parallel doubles the amp-hours and keeps the voltage the same; wiring them in series doubles the voltage and keeps the amp-hours the same. Either way the watt-hours add up, so a pair of 12V 100Ah batteries stores 2,400 Wh whether you wire it for 12V 200Ah or 24V 100Ah.

C-Rate and Rated vs Usable Capacity

A battery's amp-hour rating is not a single fixed number; it depends on how fast you pull the current. Engineers describe discharge speed as a C-rate: a 1C rate empties a fully charged battery in one hour, 0.5C (also written C/2) takes two hours, and 0.2C (C/5) takes five hours. Battery University notes that flooded and lead-acid batteries are rated at a gentle 0.05C, the 20-hour rate, because a slow discharge returns the highest figure for the label.

Draw current faster than that and the battery gives back fewer amp-hours. This is the Peukert effect, and the Peukert exponent puts a number on it: an ideal battery would sit at exactly 1.0, where capacity is independent of the discharge rate. Real batteries run higher. Per Peukert's law, the exponent is about 1.05 to 1.15 for AGM, 1.1 to 1.25 for gel, and 1.2 to 1.6 for cheap flooded lead-acid. Lithium (LiFePO4) sits much closer to the ideal; Victron, whose battery monitors apply this correction, notes lead-acid is more affected by the Peukert effect than lithium, so a LiFePO4 pack returns nearly its full rated capacity regardless of discharge rate.

Battery type	Typical Peukert exponent	Usable vs rated at high draw
Ideal (theoretical)	1.0	No change with rate
LiFePO4 / lithium	near 1.0	Nearly flat
AGM lead-acid	1.05 to 1.15	Small drop
Gel lead-acid	1.1 to 1.25	Moderate drop
Flooded lead-acid	1.2 to 1.6	Largest drop

What does that mean in amp-hours? Take a 100Ah flooded battery rated at the 20-hour rate (a 5A draw). Run it instead at a 4-hour rate (25A) and the Peukert formula, using lead-acid's typical exponent of 1.25, predicts only about 67Ah of usable capacity before the voltage sags. A LiFePO4 battery of the same rating would still deliver close to its full 100Ah at that load. The rule for sizing: trust the label for lithium, but derate lead-acid for anything heavier than a slow, steady draw. Our lead-acid battery runtime calculator works the full Peukert equation into a runtime estimate.

Worked Examples

Converting a 100Ah Battery Back to Watt-Hours and mAh

Context

You have a 100Ah 12V LiFePO4 battery and want two other figures: its watt-hours (for airline rules and cross-voltage comparison) and its milliamp-hours (to compare against a power bank).

Calculation

Watt-hours: 100 Ah x 12 V = 1,200 Wh

Milliamp-hours: 100 Ah x 1,000 = 100,000 mAh

Interpretation

The same battery is 1,200 Wh and 100,000 mAh: identical capacity expressed in three different units. At 1,200 Wh it is twelve times the 100Wh airline carry-on limit, so it cannot fly in a carry-on without special approval.

Takeaway

If your battery is labeled only with a reserve-capacity rating in minutes instead of amp-hours, our reserve capacity to Ah converter turns that figure into Ah.

Converting an E-Bike Battery Spec to Ah

Context

Your e-bike battery is rated 720Wh at 48V. You want to know the amp-hour capacity to compare it against replacement options listed in Ah.

Calculation

Ah = 720 Wh / 48 V = 15 Ah

Interpretation

The battery is 15Ah. A replacement rated at 20Ah would be 960Wh — 33% more range per charge, assuming the same motor efficiency. To see how that translates to real-world distance, plug those numbers into the e-bike battery range calculator.

Takeaway

For power banks and smaller batteries rated in mAh, remember that 1 Ah = 1,000 mAh. A 20,000mAh bank at 3.7V is 74 Wh. See our power bank runtime calculator for more detail.

Frequently Asked Questions

Glossary

Ampere-Hours

A measure of electric charge capacity. One amp-hour means the battery can deliver 1 amp for 1 hour, or 2 amps for 30 minutes. Ah only tells you capacity at a specific voltage — you need both Ah and voltage to calculate total energy.

Watt-Hours

A measure of total energy. Wh = Ah x V. Unlike amp-hours, watt-hours let you compare batteries of different voltages directly. A 50Ah 24V battery (1,200 Wh) stores the same energy as a 100Ah 12V battery (1,200 Wh).

Nominal Voltage

The average voltage a battery delivers during normal use. A "12V" lead-acid actually ranges from 10.5V to 12.7V. A "12V" LiFePO4 ranges from 10V to 14.6V. The nominal value is used for capacity calculations.

Sizing a solar system? The solar battery bank size calculator uses amp-hour figures to match storage to your panels.

Converting between amp-hours and watt-hours is the foundation of every battery sizing calculation. Get this step right — and always compare at the same voltage — and the rest of your system design falls into place. Our battery runtime guide walks through how amp-hours translate into real-world runtime across different battery chemistries and load scenarios.

More Battery calculators

Browse all battery calculators — LiFePO4, lead-acid, AGM, and lithium-ion runtime, charge time, and capacity sizing.

Last updated: May 30, 2026

Written and maintained by Dan Dadovic, Commercial Director at Ezoic Inc. & PhD Candidate in Information Sciences. He works professionally as Commercial Director at Ezoic Inc., leading revenue strategy across digital publishing.

Disclaimer: Calculator results are estimates based on theoretical formulas. Actual performance varies with temperature, battery age, load patterns, and equipment condition. For critical electrical work, consult a licensed electrician.

Editorial review by Doc. dr. sc. Damir Topić, Assistant Professor, FERIT Osijek.