Battery Capacity Calculator

Professional online calculator for battery capacity, energy, and voltage

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Good to know

What is battery capacity?

The capacity of a battery indicates how much electrical energy it can store. It is crucial for the runtime of a device and is usually given in ampere-hours (Ah) or milliampere-hours (mAh).

Important units
  • Capacity (C): Ah, mAh, C
  • Energy (E): Wh, kJ
  • Voltage (U): V
Example calculation

A battery supplies 12 V voltage and stores 72 Wh energy.

\[\displaystyle \text{Capacity} = \frac{\text{Energy}}{\text{Voltage}} = \frac{72 \text{ Wh}}{12 \text{ V}} = 6 \text{ Ah}\]
Basic formulas
\[E = C \times U\]
\[C = \frac{E}{U}\]
\[U = \frac{E}{C}\]
E = Energy, C = Capacity, U = Voltage

Description of battery capacity

To calculate the capacity of a battery, we need some information, such as the voltage (U) and the required discharge time or current consumption. Usually, the capacity is given in ampere-hours (Ah) or milliampere-hours (mAh). Here is the basic formula:

\[\displaystyle \text{Capacity (Ah)} = \frac{\text{Energy (Wh)}}{\text{Voltage (V)}}\]

If the energy is given in watt-hours (Wh), simply divide it by the voltage in volts (V).

Formulas for battery capacity

Calculation with watt-hours (Wh)

If the energy is known in watt-hours (Wh) and the voltage in volts (V), the capacity in ampere-hours (Ah) can be calculated as follows:

\[\displaystyle \text{Capacity (Ah)} = \frac{\text{Energy (Wh)}}{\text{Voltage (V)}}\]
Calculation with current and time

If the current (I) in amperes and the time (t) in hours are known, the capacity can be calculated directly:

\[\displaystyle \text{Capacity (Ah)} = I \times t\]
Example 1

If a device is operated with 2 A for 3 h, then the capacity of the battery is:

\[\text{Capacity} = 2 \text{ A} \times 3 \text{ h} = 6 \text{ Ah}\]
Example 2

If the voltage of the battery is 12 V and the energy is 72 Wh, then the capacity is:

\[\text{Capacity} = \frac{72 \text{ Wh}}{12 \text{ V}} = 6 \text{ Ah}\]
The formulas summarized
\[\displaystyle E = C \cdot U\]
Energy = Capacity × Voltage
\[\displaystyle C = \frac{E}{U}\]
Capacity = Energy / Voltage
\[\displaystyle U = \frac{E}{C}\]
Voltage = Energy / Capacity
Unit conversions

The unit of energy is watt-hours (Wh) or kilojoules (kJ)

\[1 \text{ Wh} = 3{,}6 \text{ kJ}\]

The unit of capacity is milliampere-hours (mAh) or coulombs (C)

\[1 \text{ mAh} = 3{,}6 \text{ C}\]

The unit of voltage is volt (V)

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Battery Capacity  •  Capacitor Capacitance  •  Decibel, votage, power converter  •  Decibel - factor converter  •  Electric Power  •  Electric Energy  •  Electric Charge  •  Electrostatic force, Coulombs Law  •  Internal resistance of a power source  •  Ohm's law and power  •  Table of temperature coefficients  •  Temperature drift of resistance  •  Voltage drop  •  Wire resistance  •