What size power bank do I need for travel?

For phone-only top-ups, a 10,000mAh pack gets most users two to three full phone charges and slips into a pocket. For laptops, tablets, or multi-day trips, step up to 20,000–27,000mAh, but stay under 100Wh (roughly 27,000mAh at 3.7V) to remain TSA-compliant for carry-on. Anything labeled 'flight-approved' or 'TSA-approved' by the manufacturer is sized below that limit.