How to quickly calculate the wattage of any iPhone charger

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How to calculate wattage of iPhone charger
A simple calculation is all you need.
Image: Killian Bell/Cult of Mac

Looking for an iPhone charger that will deliver the fastest possible charging speeds? Forget the one that came bundled with your old iPhone and pick up a super-speedy 20W adapter instead.

If you can’t find the wattage of an adapter in its product description, we’ll show you a quick and easy way to calculate it yourself so you don’t waste your hard-earned cash on the wrong one.

Before Apple stopped bundling chargers with iPhone, most devices shipped with a 5W plug. But all are capable of receiving a lot more power for a significantly faster charge. Some larger iPhone models can take up to 22W of power, but the general rule is a 20W adapter is ideal.

20W will give you the fastest possible charging speeds with almost all iPhone models — not only when charging with a cable, but when topping up wirelessly with Apple’s official MagSafe Charger, too. Here’s how to ensure the adapter you have your eye on is powerful enough.

How to calculate the wattage of any iPhone charger

Fortunately, wattage is one of the details you’ll see listed in the product description for most charging adapters. But if you stumble upon an adapter you like the look of and this information is missing, you can calculate the wattage yourself in no time at all.

All you need to do is look for the adapter’s maximum voltage and amps. Take these two figures and multiply them, and you’ll find out the adapter’s maximum wattage. For instance, if your plug can deliver 9 volts at 2 amps, its maximum wattage is 18W.

There’s no need to worry about buying a charger that’s too powerful. All iPhone models have built-in protections that ensure they do not pull too much power — even if a charger can deliver it. Which is why it’s perfectly safe to charge your iPhone with a 60W MacBook adapter.

Avoid wireless charging?

If you really want the fastest possible charger for your iPhone, another tip is to avoid wireless charging altogether. Wireless charging pads are substantially slower than cables, including Apple’s pricey MagSafe puck, which maxes out at 15W with iPhone 12, or 12W with iPhone 12 mini.

Most wireless charges, even the pricier MagSafe Duo, are even less powerful than this, typically offering between 5W and 12W. You may find dual or even triple charging pads that advertise a higher wattage than this, but that’s usually because that is shared among multiple devices.