Battery Capacity Calculator
Calculate battery capacity from voltage, current, and discharge time. Determine capacity in mAh, Ah, and watt-hours.
How to Use This Calculator
- Enter the battery voltage in volts (e.g., 3.7V for Li-ion, 1.2V for NiMH).
- Enter the discharge current in milliamperes (mA).
- Enter the discharge time in hours until the battery reaches cutoff voltage.
- The calculator displays capacity in mAh, Ah, and watt-hours (Wh).
Battery Capacity Formula
Battery capacity is calculated from current and time:
Capacity (Ah) = Capacity (mAh) / 1000
Energy (Wh) = Voltage (V) × Capacity (Ah)
Example: Battery discharged at 1000mA for 2.5 hours at 3.7V: Capacity = 1000 × 2.5 = 2500 mAh = 2.5 Ah. Energy = 3.7 × 2.5 = 9.25 Wh.
Full Description
Battery capacity is a measure of how much charge a battery can store and deliver. It's typically measured in milliampere-hours (mAh) or ampere-hours (Ah), which represent the amount of current a battery can supply for a specific duration. Understanding battery capacity is essential for selecting the right battery for your application, estimating runtime, and comparing different battery types.
Capacity depends on the discharge rate—higher discharge rates typically result in lower usable capacity due to internal resistance and chemical limitations. This is why battery specifications often include capacity at different C-rates (where 1C = the current that would discharge the battery in 1 hour). Watt-hours (Wh) is another useful measure that accounts for voltage, making it easier to compare batteries with different voltages.
This calculator helps you determine battery capacity from discharge measurements. Enter voltage, current, and discharge time, and it calculates capacity in mAh, Ah, and Wh. Use it when testing batteries, understanding specifications, or selecting batteries for your projects. Remember that actual capacity may vary with discharge rate, temperature, and battery age.
Frequently Asked Questions
How is battery capacity calculated?
Capacity (mAh) = Current (mA) × Time (hours). For example, a battery that supplies 1000mA for 2.5 hours has a capacity of 2500 mAh. Watt-hours (Wh) = Voltage (V) × Capacity (Ah).
What's the difference between mAh, Ah, and Wh?
mAh (milliampere-hours) and Ah (ampere-hours) measure charge capacity. Wh (watt-hours) measures energy capacity. mAh = Ah × 1000. Wh = V × Ah. Wh accounts for voltage, making it better for comparing batteries with different voltages.
How do I measure battery capacity?
Discharge the battery at a constant current while measuring voltage and time. Capacity = Current × Time until voltage drops to cutoff. Use a battery capacity tester or multimeter with current measurement. Be careful with lithium batteries.
Why does capacity vary with discharge rate?
Batteries show lower capacity at higher discharge rates due to internal resistance and chemical limitations. This is called the C-rate effect. A 2000mAh battery might only deliver 1800mAh at 2C (4000mA) but 2000mAh at 0.5C (1000mA).