Battery Capacity Calculator
Convert battery energy to capacity in mAh.
Battery capacity in mAh comes from its energy and voltage.
How the Math Works
The Battery Capacity Calculator uses the fundamental relationship between energy, voltage, and capacity expressed as mAh = Wh / V * 1000. This formula derives from the definition that watt-hours (Wh) equals volts (V) multiplied by amp-hours (Ah). Since battery capacity is typically measured in milliamp-hours (mAh), we multiply by 1000 to convert from amp-hours to milliamp-hours. The calculation essentially determines how much electrical charge a battery can deliver at a given voltage to produce a specific amount of energy.
Practical Applications
To use this calculator practically, first identify the energy rating of your battery in watt-hours (Wh) from the manufacturer specifications. Next, determine the battery's nominal voltage (V), which is typically listed on the product label or in technical documentation. Simply divide the energy by the voltage and multiply by 1000 to get the capacity in milliamp-hours. For example, a 100 Wh laptop battery operating at 14.8 V would have a capacity of approximately 6,757 mAh.
Day-to-Day Use
This calculation is essential when comparing different battery options for your devices, helping you make informed purchasing decisions based on runtime expectations rather than just energy content. It's particularly useful when replacing batteries where specifications may vary, ensuring you select a compatible battery with adequate capacity for your needs. Whether you're choosing a power bank, laptop battery, or phone charger, understanding capacity in mAh allows you to estimate how long devices will run and compare the value proposition of different battery solutions in your everyday electronics usage.
Worked example
37 Wh at 3.7 V is 10000 mAh.
FAQ
Why compare in Wh?
mAh alone ignores voltage; watt-hours compare true energy across batteries.