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.

Battery Amp Hours Calculator — Free

3 min read

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

Notice the pattern: doubling the voltage halves the amp-hours for the same energy. This is why higher-voltage systems use smaller cables — the current is lower for the same power.

Worked Examples

Comparing Batteries Listed in Different Units

Context

Battery A is listed as 100Ah at 12V. Battery B is listed as 1,500 Wh. Which has more capacity?

Calculation

Battery A: 100 Ah x 12 V = 1,200 Wh

Battery B: 1,500 Wh / 12 V = 125 Ah (if 12V)

Interpretation

Battery B has 25% more energy (1,500 vs 1,200 Wh). But the comparison only works if both operate at the same voltage. If Battery B is 24V, it is only 62.5 Ah — fine for a 24V system but incompatible with 12V devices.

Takeaway

Always compare in watt-hours when batteries use different voltages. To check how this translates to usable amp-hours at a given DoD, use our reserve capacity to Ah converter.

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 <a href="/solar/solar-battery-bank-size-calculator">solar battery bank size calculator</a> 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.

Last updated: March 16, 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.