How to Use the Power Bank Capacity Calculator
Travel drains your phone battery much faster than usual — maps, photos, and social media all add up. This calculator takes your phone and any secondary device's battery capacity and how many charges you need per day, then estimates the power bank capacity (mAh) you'll need to get through the day without an outlet.
Power banks lose energy in voltage conversion, so only about 70% of a power bank's rated capacity actually reaches your device. For example, fully charging a 4,000mAh phone twice a day takes 8,000mAh in theory, but accounting for that loss you'd want a power bank rated at roughly 11,500mAh or more.
This result covers one day of use. If your trip includes multi-day stretches without an outlet — like trekking or camping — multiply the result by the number of days to size up accordingly. Also check your airline's carry-on limit (100Wh, roughly 27,000mAh) before you pack.
Frequently Asked Questions
Power delivered from a power bank to your device loses energy in voltage conversion, so only about 60-70% of the rated capacity actually reaches your device. This calculator adds that loss back in to recommend a rated capacity that's actually enough.
Most airlines allow power banks up to 100Wh (roughly 27,000mAh at 3.7V) in carry-on baggage, but not in checked luggage. Rules vary by airline, so check with yours before you fly.