Power Bank Size Calculator
Find the right power bank capacity for your devices.
Calculate how many full charges you can get based on mAh, device battery size, and charging efficiency.
Power bank capacity is measured in milliampere-hours (mAh). But the rated mAh on the label is not what your device actually receives.
Why you get less than the rated capacity: Power banks store energy at 3.7V (lithium battery voltage). Your phone charges at 5V via USB. This voltage step-up conversion loses energy — typically 10–15%. Add heat loss and self-discharge, and real-world efficiency is usually 85–90% for quality banks and 75% for budget or older models.
The core formula:
Usable mAh = Rated mAh × Efficiency
Full Charges = Usable mAh ÷ Device Battery mAh
Choosing the right power bank size:
- 5,000 mAh — Ultra-compact. Fits in a pocket. Gives roughly 1 full phone charge. Good for day trips.
- 10,000 mAh — The everyday carry sweet spot. Provides 2–3 phone charges. Fits in a bag easily.
- 20,000 mAh — Travel size. Handles 4–6 charges. Good for long flights or multi-day trips.
- 30,000+ mAh — Group or camping use. Heavy but powerful. Can charge multiple devices.
Common device battery sizes for reference:
- iPhone 15: ~3,300 mAh
- Samsung Galaxy S24: ~4,000 mAh
- Google Pixel 8: ~4,575 mAh
- iPad Air (M2): ~7,600 mAh
- AirPods Pro (case): ~345 mAh
- Kindle Paperwhite: ~1,750 mAh
Fast charging note: Fast charging (USB-PD, Quick Charge) transfers energy more efficiently in some cases, but also generates more heat. Always use the cable and adapter recommended for your device.
A 10,000 mAh power bank is the most popular size worldwide — it balances capacity, weight, and portability perfectly for most users.