Find out how many times a power bank will really charge your phone. Pick the power bank size and your phone: the calculator shows the real number of full charges (not the number on the box), how much energy actually reaches your phone, and whether you can take the power bank on a plane.
A 20,000 mAh power bank charges a typical phone
2.7 full charges
Real-world range: 2.3 to 3.1 · or about 4.5 top-ups from 20% to 80%
Why not more? The label counts the cells at 3.7 V. Turning that into the 5 to 9 V your phone takes, plus heat in the cable and the phone, loses about 20% to 40%. How we calculate
In stock at Mobile Geeks for a typical phone
Cash on delivery across Pakistan · 7-day returns
How the calculator works
The mAh on a power bank is counted at its cells, which run at about 3.7 volts. Your phone’s battery runs at about 3.85 volts, and the power bank has to raise its voltage to the 5 to 9 volts your phone takes in. Every step loses some energy as heat, in the power bank, the cable and the phone. So the calculator compares energy in watt-hours (Wh), not mAh:
- Power bank energy = mAh × 3.7 ÷ 1000. A 20,000 mAh power bank holds 74 Wh.
- Phone battery energy = mAh × 3.85 ÷ 1000. A 5,000 mAh phone holds about 19.3 Wh.
- About 70% of the power bank’s energy reaches the phone’s battery: 60% to 80% depending on the power bank, the cable and the heat.
- Full charges = 74 × 0.7 ÷ 19.3, about 2.7.
Using the phone while it charges, hot weather and an old battery all lower the number.
Which size should you buy?
- 10,000 mAh: about 1.3 full charges of a 5,000 mAh phone. Fits a pocket, good for daily top-ups.
- 20,000 mAh: about 2.7 full charges. Good for travel, long days and power cuts.
- 27,000 mAh and above: for laptops and several devices. Check the watts too: most laptops need 45 W to 100 W over USB-C. Above about 27,000 mAh a power bank is over 100 Wh, so most airlines will not take it.
Compare the two most popular sizes in 10000mAh vs 20000mAh power bank, read the best power banks in Pakistan for fast charging, or see all power banks with cash on delivery across Pakistan.
Flying with a power bank
A power bank always goes in your hand luggage, never in a checked bag. Since March 2026 the international rules (ICAO) allow at most two power banks per passenger, and you may not charge them on board. Up to 100 Wh (about 27,000 mAh) is allowed. IATA now lists power banks between 100 and 160 Wh as not allowed for passengers, though some airlines accept them with approval until the end of 2026, and above 160 Wh is never allowed. Many airlines, Emirates among them, also do not let you use a power bank during the flight, so check with your airline before you fly.
Questions
How many times will a 10000mAh power bank charge my phone?
About 1.3 times for a phone with a 5,000 mAh battery, and about 2 times for an iPhone 15 (3,349 mAh). Pick your phone in the calculator for its own number.
How many times will a 20000mAh power bank charge my phone?
About 2.7 times for a 5,000 mAh phone and about 4 times for an iPhone 15.
Why do I get fewer charges than the mAh suggests?
The mAh on the box is counted at the cells’ 3.7 volts, and 20% to 40% of the energy turns into heat while the power bank raises the voltage and the phone charges. A good power bank loses less, but none gives the full number.
Can I take a 30000mAh power bank on a plane?
Usually not. 30,000 mAh is about 111 Wh, over the 100 Wh limit for power banks. A 20,000 mAh power bank (74 Wh) is allowed in your hand luggage.
Can I put this calculator on my website?
Yes, it is free. Open “Embed this calculator on your website” under the calculator and paste the code into your page.
