Battery Capacity Calculator (Amp Hours)

Calculate battery capacity in amp-hours, voltage, or energy by entering any two values in Wh, kWh, V, mV, Ah, or mAh for batteries.

Battery Capacity Formula

The battery capacity calculator uses watt-hours, voltage, and amp-hours. Enter any two values to calculate the missing value.

Wh = V * Ah

Ah = Wh / V

V = Wh / Ah

Wh = total energy in watt-hours
V = battery voltage in volts
Ah = battery capacity in amp-hours

The calculator also handles common unit conversions before applying the formula:

1 kWh = 1000 Wh

1 mAh = 0.001 Ah

1 mV = 0.001 V

To calculate total energy: voltage is multiplied by amp-hours to get watt-hours.
To calculate amp-hours: total energy in watt-hours is divided by voltage.
To calculate voltage: total energy in watt-hours is divided by amp-hours.
For kWh, mAh, or mV: the value is converted to Wh, Ah, or V first, then converted back to the unit you selected.

Common Battery Voltage and Capacity Reference

These examples show typical battery ratings and the approximate energy they store. Actual usable energy can be lower depending on discharge limits, battery chemistry, age, and load.

Battery type or use	Typical voltage	Example capacity	Approx. energy
Single lithium-ion cell	3.7 V	3000 mAh	11.1 Wh
USB power bank	3.7 V cell rating	10000 mAh	37 Wh
Car battery	12 V	50 Ah	600 Wh
Small solar battery	12 V	100 Ah	1200 Wh, or 1.2 kWh
48 V battery bank	48 V	100 Ah	4800 Wh, or 4.8 kWh

Battery Unit Conversions

Conversion	Use this when
mAh ÷ 1000 = Ah	A small battery is rated in milliamp-hours.
Ah × 1000 = mAh	You want to express amp-hours as milliamp-hours.
kWh × 1000 = Wh	A larger battery is rated in kilowatt-hours.
Wh ÷ 1000 = kWh	You want to express watt-hours as kilowatt-hours.

Example Calculations

Example 1: Calculate watt-hours from volts and amp-hours

You have a 12 V battery rated at 100 Ah.

Wh = V * Ah

Wh = 12 * 100 = 1200 Wh

The battery stores about 1200 Wh, or 1.2 kWh.

Example 2: Calculate amp-hours from watt-hours and voltage

You have a battery rated at 720 Wh and 24 V.

Ah = Wh / V

Ah = 720 / 24 = 30 Ah

The battery capacity is 30 Ah.

FAQ

What is the difference between amp-hours and watt-hours?

Amp-hours measure electric charge capacity. Watt-hours measure stored energy. Amp-hours alone do not tell you the total energy unless you also know the voltage. For example, a 10 Ah battery at 12 V stores 120 Wh, while a 10 Ah battery at 24 V stores 240 Wh.

How do you convert mAh to Wh?

First convert mAh to Ah by dividing by 1000. Then multiply by voltage.

Wh = V * (mAh / 1000)

For example, a 5000 mAh battery at 3.7 V is 5 Ah × 3.7 V = 18.5 Wh.

Does the calculated capacity equal the usable battery capacity?

Not always. The calculation gives the rated or theoretical energy based on voltage and amp-hours. Usable energy can be lower because of inverter losses, voltage cutoff, temperature, battery age, and recommended depth of discharge.