USB-C Charging Wattage Guide
Charging wattage is one of the few specs where more is not automatically better, and where the number printed on the charger is often not the number you actually get. Here is what the figures mean in practice.
How many watts each device needs
| Device | Useful wattage | Above this gains you |
|---|---|---|
| Wireless earbuds | 5W | Nothing |
| Apple Watch and most smartwatches | 5W | Nothing (see the fast-charge exception below) |
| Phone, standard charging | 10–12W | Faster top-ups |
| Phone, fast charging | 20–30W | Nothing — phones cap themselves |
| Tablet (iPad, Galaxy Tab) | 20–30W | Marginal |
| 13-inch laptop (MacBook Air class) | 30–45W | Faster charging while in use |
| 15–16-inch laptop | 65–100W | Faster charging under load |
The pattern: for everything most people carry — phone, watch, earbuds, tablet — 30W is the ceiling that matters. Wattage above that is a laptop feature.
Why your fast charger feels slow
Four causes, in the order we actually see them:
- The cable is the bottleneck. USB-C cables are not interchangeable. A cable built for 15W will hold the entire connection at 15W even if the charger can supply 65W. This is by far the most common cause and the hardest to spot, because the cable looks identical.
- You are charging through a USB-A port. Laptop ports, car ports and older wall bricks with a rectangular USB-A socket rarely exceed 12W. The port shape tells you the ceiling.
- Two devices are sharing one charger. A 30W dual-port charger is 30W in total, not 30W per port.
- The battery is above 80 percent, or the phone is warm. Every phone deliberately slows charging in both cases to protect the cell. This is normal behaviour, not a fault.
What 60W, 100W and 240W actually mean on a cable
- 60W — up to 3A at 20V. No special chip required. Covers every phone, every tablet, every watch, and most 13-inch laptops.
- 100W — 5A at 20V. Requires an e-marker: a small chip inside the connector that tells the charger the cable is rated for 5A. A cable without one will not be allowed above 3A, whatever the packaging claims.
- 240W — 5A at 48V, under the Extended Power Range part of the USB-C spec. Also requires an e-marker, and requires both the charger and the device to support EPR. In practice this is for large laptops and a handful of monitors.
If you are buying a cable for a phone, the honest answer is that 60W is enough and the higher numbers change nothing about how fast your phone charges.
How to pick, in one paragraph
Buy a 30W charger and a 60W cable. That combination charges any phone at full speed, any tablet at a sensible speed, a watch and earbuds at their maximum, and a light laptop slowly but usefully. Buy above that only when you have a specific laptop that needs it.
See the wall chargers and charging cables.
Frequently asked questions
How many watts do I need to fast-charge an iPhone?
20W is the practical floor, and 30W covers every current model at full speed. Above 30W gives no further benefit on a phone, because the phone requests the power rather than the charger pushing it.
Why does my fast charger feel slow?
Most often the cable. A USB-C cable that only supports 15W will cap the whole connection at 15W regardless of the wall plug. The second most common cause is charging through a USB-A port on a laptop or in a car, which rarely exceeds 12W.
What does a 60W cable rating mean?
A 60W USB-C cable carries up to 3A at 20V. That covers every phone and tablet and most 13-inch laptops. Cables rated above 60W carry 5A and need an internal e-marker chip.
Do I need a 100W or 240W cable?
Only for charging a large laptop at full speed. For phones, tablets, watches and earbuds a 60W cable is never the bottleneck.
Can a higher-wattage charger damage my phone?
No. USB Power Delivery is a negotiation: the device requests a voltage and current and the charger supplies only what was agreed. A 100W charger connected to a phone that asks for 20W delivers 20W.