How to Calculate mAh to Wh for 20000mAh Battery Regulations
Updated 2026-08-25 · Power Bank Guide
When you need to know whether a 20000mAh power bank can fly with you, the first step is to convert mAh to Wh power bank specifications. The conversion tells you if the battery falls under the TSA/FAA 100 Wh carry‑on limit and helps you estimate real‑world charging performance. This guide breaks down the math, explains what the numbers really mean, and shows how a 22.5W PD output translates into everyday charging speed.
How to Convert mAh to Wh
Portable chargers use lithium‑ion cells that operate at a nominal voltage of 3.7 V. To turn milliamp‑hours (mAh) into watt‑hours (Wh), use the simple formula:
- Wh = (mAh ÷ 1,000) × 3.7 V
For a 20000 mAh bank, the calculation is:
(20,000 ÷ 1,000) × 3.7 V = 20 Ah × 3.7 V = 74 Wh
At 74 Wh, the pack is comfortably below the 100 Wh limit that most airlines enforce for carry‑on luggage. Always double‑check your airline’s policy before boarding, but the math shows you’re in the safe zone.
What 20000mAh Really Means
Manufacturers quote the raw cell capacity (20 Ah), not the usable energy after conversion to the 5 V USB output. Internal voltage‑boost circuitry introduces losses, typically 30‑40 % for a quality bank. Assuming a 65 % efficiency, the usable energy is:
74 Wh × 0.65 ≈ 48 Wh
This is the amount that actually reaches your device. The figure is useful for estimating how many full charges you’ll get from common smartphones.
Real‑World Charges per Device
Take a few popular phones as examples. Battery capacities are approximate:
- iPhone 17: 3,300 mAh (≈12 Wh)
- Samsung Galaxy S24: 4,800 mAh (≈18 Wh)
- Google Pixel 8 Pro: 5,000 mAh (≈19 Wh)
- Xiaomi Mi 13: 5,000 mAh (≈19 Wh)
Dividing the usable 48 Wh by each phone’s battery gives a realistic charge count:
- iPhone 17 – about 4 full charges
- Galaxy S24 – about 2.5 full charges
- Pixel 8 Pro – about 2.5 full charges
- Mi 13 – about 2.5 full charges
These numbers assume 65 % efficiency and a fully depleted phone each time; real‑world usage will vary based on screen-on time, background apps, and temperature.
Understanding 22.5W PD Fast Charging
USB‑C Power Delivery (PD) negotiates voltage and current to deliver up to 22.5 W on many 20000 mAh power banks. The most common PD profile for 22.5 W is 9 V × 2.5 A. At that rate, you can estimate charging time for a typical phone:
Battery energy ÷ 22.5 W = hours. For an iPhone 17 (12 Wh): 12 Wh ÷ 22.5 W ≈ 0.53 h, or about 32 minutes for a 0‑100 % charge under ideal conditions.
In practice, the phone’s internal charging circuitry limits the speed, especially after 80 % capacity. Expect 0‑80 % in roughly 20‑25 minutes, then a slower top‑up phase.
The same 22.5 W output can also charge laptops that accept USB‑C PD, such as a 13‑inch MacBook Air (30 Wh). At 22.5 W it would take roughly 1.5 hours to reach 80 %.
Why the INIU 20000mAh Portable Charger Is a Good Choice
If you need a flight‑safe, pocket‑sized charger that actually delivers the numbers discussed above, the INIU 20000mAh Portable Charger (Flight‑Safe) checks the boxes. Its 74 Wh rating stays under the 100 Wh TSA limit, and the built‑in 22.5 W PD output matches the fast‑charging profile we covered. The package includes a USB‑C cable and a flashlight—handy for travel situations where you might not have a spare cable.
Because the unit’s efficiency is listed at about 65 %, you can expect the same 4 iPhone 17 charges or 2.5 Galaxy S24 charges that the calculations predict. Its compact design fits in a jacket pocket, and the airline‑friendly rating means you won’t have to check it in.
Other Specs to Watch When Choosing a Power Bank
Beyond capacity and PD wattage, consider these factors:
- Input charging speed: A 20 W or higher USB‑C input will refill the 20000 mAh pack in 4‑5 hours from a wall outlet.
- Number of ports: Dual USB‑A ports let you charge two devices simultaneously, but the total output will split the available wattage.
- Safety features: Look for over‑charge, over‑discharge, short‑circuit, and temperature protection.
- Build quality: A rugged shell or silicone coating adds durability for travel.
All of these specs interact with the core capacity and 22.5 W PD rate to determine how useful the charger is in real life.
FAQ
Do I need to declare a 20000mAh power bank when flying?
Most airlines allow up to 100 Wh in carry‑on luggage without declaration. A 20000 mAh bank is about 74 Wh, so it generally does not require special paperwork, but always verify with your carrier before travel.
Why does the usable capacity differ from the labeled mAh?
The mAh rating reflects the internal cell voltage (3.7 V). When the bank steps the voltage up to 5 V for USB output, conversion losses and boost‑converter inefficiency reduce the energy that actually reaches your device, typically leaving 60‑70 % of the original rating usable.
Can I use a 22.5W PD power bank to charge a laptop?
Yes, as long as the laptop accepts USB‑C PD at 9 V × 2.5 A or lower. Expect slower charge times than a dedicated laptop charger, but you can still get meaningful power—enough for a few hours of work or to top up the battery during a coffee break.