Interactive Battery & Flight Tool

Power Bank Real Capacity (mAh to Wh), Charge Count & Airline 100Wh Calculator

Why does a 20,000mAh power bank only charge a 5,000mAh phone ~2.6 times instead of 4? Internal cells store energy at 3.7V before stepping up to 5V–20V USB-PD. Calculate exact usable watt-hours, device charges, and FAA/TSA carry-on legality below.

Nominal Energy (Wh)74.0 Wh
Delivered Usable Energy60.7 Wh
Full 0–100% Charges3.3×
FAA / TSA Carry-OnLEGAL (≤100Wh)
At 74.0 Wh (3.7V cell standard), this pack passes every international airport checkpoint in carry-on luggage with no airline approval required.
4-in-1 Magnetic Desk & Nightstand Charging Dock

Eliminate wireless coil heat on your nightstand—charges phone, watch & earbuds simultaneously.

View In-Stock Spec ($39.99) →
Compare Tested 10K, 20K & 65W Laptop Power Banks

See our full hands-on roundup of TSA-legal fast-charging packs and Prime picks.

Read Power Bank Guide →

The Exact Formula Behind Power Bank mAh vs. Real Charges

Manufacturers print capacity in milliamp-hours (mAh) referenced to the internal lithium-ion cell\'s nominal 3.7V chemistry. To convert mAh to watt-hours (Wh)—the unit airlines and physics actually care about—multiply mAh × 3.7 ÷ 1,000. During discharge, internal DC-DC boost converters step 3.7V up to 5V, 9V, 15V, or 20V USB Power Delivery, losing roughly 15%–20% as conversion heat over a cable (or 35%–40% across wireless Qi/MagSafe coils). Read more in our Power Bank Sizing Guide and Charger & Power Bank Specs Explained.