USB-C chargers do not have a single output voltage. They offer a list of levels, and the laptop picks one through the Power Delivery negotiation. Which levels a charger offers depends on its rated power, and the cable can limit the current. This calculator lists the standard fixed levels for a given charger and cable, and checks whether the result is enough for a laptop.
How to use it
- Enter the charger's rated power from its label.
- Choose the cable: a standard cable carries up to 3 A; a 5 A e-marked cable is needed above 60 W at 20 V; an EPR cable is needed for the 28, 36 and 48 V levels above 100 W.
- Optionally enter what the laptop needs (from its original charger).
- Read the table of available levels and the verdict.
How the levels are set
Under the Power Delivery rules for fixed supplies, a charger offers:
| Rated power | Levels offered |
|---|---|
| Up to 15 W | 5 V |
| Above 15 W | 5 V and 9 V |
| Above 27 W | 5 V, 9 V and 15 V |
| Above 45 W | 5 V, 9 V, 15 V and 20 V |
| Above 100 W (EPR) | adds 28 V, then 36 V and 48 V at higher ratings |
Up to 20 V, current is limited to 3 A on standard cables, which caps 20 V at 60 W. Above that, the charger and cable must both support 5 A. Most laptops charge only from 20 V; some also accept 15 V at reduced power.
Some chargers also offer programmable (PPS) ranges; those are not shown here because laptops rarely use them.
Worked example
A 65 W charger with a standard 3 A cable gives 20 V at 3 A — 60 W, not 65 W. With a 5 A cable it can deliver the full 65 W (20 V, 3.25 A). For a laptop that needs 65 W, the difference is small; for a 100 W laptop on a 65 W charger, expect slow charging or charging only while idle. Diagnosing laptops that will not charge from USB-C is covered in USB-C Laptop Not Charging: PD Controller Diagnosis, and the standard under usb power delivery.
FAQ
Why does my 65 W charger show 60 W on a USB meter?
The cable is probably limited to 3 A, which caps 20 V at 60 W.
Can a phone charger charge a laptop?
Some laptops accept low power slowly; many refuse anything below a minimum such as 30–45 W.
Do I need a special cable for 100 W?
Yes: a 5 A e-marked cable. For above 100 W, an EPR-rated cable.