How many watts does your phone really need?

Charger boxes shout numbers: 20W, 33W, 45W, 65W. It is easy to think bigger is always better, or to worry that a big charger will harm a small phone. Neither is quite right. Here is how to pick the right wattage in two minutes.

Who decides the charging speed?

Your phone does. When you plug in, the phone and charger agree on a speed through a standard such as USB Power Delivery (PD) or Programmable Power Supply (PPS). The phone asks for what its battery can take and the charger supplies that, up to its own limit. So a 65W charger charges a phone built for 20W at about 20W.

Which charger fits my phone?

How do I find my phone's top speed?

• Open your phone's specificationsOn the maker's website or the box.
• Find the wattageFor example 25W or 45W.
• Find the standardPD, PPS, or a brand's own system.

Why is my phone charging slower than the charger's rating?

Three common reasons: the cable is rated for less power than the charger, the battery is warm (phones slow down to protect it), or the battery is above about 80%, where every phone slows down on purpose.