How many mAh do I need in a power bank?

For topping up a phone once or twice, reviewers across specialist communities favor a 10,000mAh class pack for the best size-to-capacity balance. For multi-day trips or charging a laptop, the consensus points to 20,000–26,000mAh packs, with the caveat that real usable capacity is always lower than the printed rating due to voltage conversion losses.