About

Portable electronics, from smartphones to laptops, utilize lithium-ion batteries rated in differing units. While consumers are accustomed to seeing capacity in milliamp-hours (mAh), regulatory bodies like the FAA or TSA define air travel safety limits in Watt-hours (Wh)-typically capping carry-on batteries at 100Wh. This discrepancy creates confusion for travelers trying to determine if their 20,000 mAh power bank is legal to fly.

This tool converts energy ratings back into the milliamp-hour format used on device specifications. It is critical to input the correct voltage; most USB power banks use 3.7V internal cells, even if they output 5V. Using the output voltage (5V) instead of the nominal cell voltage (3.7V) will result in an incorrect capacity calculation, potentially misrepresenting the device's true capabilities.

Formulas

To convert energy back to milliamp-hour capacity, we divide by voltage and scale by 1000:

Q_mAh =

(

E_WhV

)

× 1000

Where E_Wh is Watt-hours and V is the battery voltage.

Reference Data

Device Type	Voltage (Nominal)	Energy (Wh)	Capacity (mAh)	Airline Compliance
Smart Watch	3.7 V	1.1 Wh	300 mAh	OK
Smartphone	3.7 V	11.1 Wh	3,000 mAh	OK
Tablet	3.7 V	29.6 Wh	8,000 mAh	OK
Small Power Bank	3.7 V	37 Wh	10,000 mAh	OK
Laptop (Air)	11.4 V	49.9 Wh	4,377 mAh	OK
Large Power Bank	3.7 V	74 Wh	20,000 mAh	OK
Max Carry-On	3.7 V	100 Wh	27,027 mAh	LIMIT
Large Laptop	11.1 V	99 Wh	8,919 mAh	LIMIT

Frequently Asked Questions

Almost all consumer power banks use Lithium-Ion or Lithium-Polymer cells with a nominal voltage of 3.6V or 3.7V. Even though the USB port outputs 5V, the internal calculation for capacity (mAh) is based on 3.7V.

Usually, yes. 27,000 mAh at 3.7V equals exactly 99.9 Wh, which is just under the standard 100 Wh limit set by FAA/EASA. However, always check with your specific airline as rules can vary.

Wh is a universal measure of energy. mAh depends on voltage. A 10,000 mAh drone battery (11.1V) has 3x the energy of a 10,000 mAh phone battery (3.7V). Wh treats them equally based on stored energy (danger potential).

Yes, but you must look at the bottom of your laptop to find the Voltage rating (often 10.8V, 11.4V, or 14.8V). You cannot assume 3.7V for laptops.