Battery & Charger Watt Calculator

Buying one charger for several devices? Tick what you charge at the same time and the calculator adds up the power so you can pick a charger that keeps up. Then work out how big a power bank you need for a number of phone or laptop charges, and whether it can go in your hand luggage on a plane.

Charging at the same time (typical fast-charge watts; change them to match your chargers)

Charger to look for

0 W

Device battery size

mAh

Phones are often 3,500-5,000 mAh. Check your model's specs.

Full charges you want

Power bank size

How it works

Charger watts = all ticked devices added together, rounded up to the next common charger size (30, 45, 65, 100, 140 or 200 W)
Power bank Wh = battery mAh × 3.85 V ÷ 1000 × charges ÷ 0.65 (about two-thirds reaches the device after heat and voltage losses)
Power bank mAh (as printed on the box, at 3.7 V) = Wh × 1000 ÷ 3.7
Flights: most airlines allow power banks under 100 Wh in hand luggage only; 100-160 Wh usually needs airline approval

For a multi-port charger, also check how the watts are shared: a "100 W" charger may give only 65 W to one port when two are in use.

Three things this tool can't see

Your exact devices. Real charging speed depends on each device and cable. Check the maker's spec.
Cable limits. A laptop above 60 W needs a USB-C cable rated for 100 W or 240 W (5 A).
Airline rules. Rules change and vary. Check your airline before you fly.

Free gift: want a gadget gift checklist by interest? Get it free when you join our list. Get it free

Results are rough guides based on typical figures. Specs and prices change, so check the seller's page and your device manual before you buy. Some links on this site may earn us a commission. Read our disclosure.