Battery Life Calculator
How long will that battery really last?
Enter a battery's capacity in milliamp-hours and the device's current draw in milliamps to estimate runtime. It shows decimal hours and a readable 'X hr Y min' version. Ideal for sizing power banks, checking how long a gadget lasts, or comparing batteries honestly.
How it's calculated
Runtime hours = battery capacity (mAh) ÷ current draw (mA). The decimal hours are also shown as whole hours and minutes.
Frequently asked questions
What do mAh and mA mean?
mAh (milliamp-hours) is how much charge the battery holds; mA (milliamps) is how fast the device drains it. Divide capacity by draw to get hours of runtime.
How do I find my device's current draw?
Check the charger's label or the device's spec sheet for its input current in mA or A (1 A = 1,000 mA). Power banks usually print the output per port.
What if the draw varies?
Use an average over your typical usage. A phone drawing 500 mA on calls but 150 mA idle needs its real-world average for a useful estimate.