Mobile & Electronics

USB-C Power Calculator

What a USB-C link comes to in watts at a given voltage and current - without pretending to know which profile your hardware supports.

5 inputs Free, no sign-up

Your figures

The voltage the link has settled on. Common fixed values are 5, 9, 15 and 20 V.

The current at that voltage.

From the device's own charger, if you have it.

Try an example

Result

Your result

Enter your figures and the result appears here.

Estimates only. Rates, fees and specifications change. Confirm against the official source before you rely on a figure — see our disclaimer.

About this calculator

USB-C is a connector, not a power level. The same plug carries anything from a 2.5 W trickle to 240 W, and which one you get is decided by a negotiation between the charger, the cable and the device — none of which is visible from the outside.

This works out what a given voltage and current come to. It deliberately does not tell you which Power Delivery profile your hardware supports, because that is not something any calculator can know from a wattage.

How to use this calculator

  1. Enter the voltage the link is using. If you are reading a charger label, take one of the listed pairs; if you are reading a phone's charging screen, use what it reports.
  2. Enter the current at that voltage.
  3. Optionally enter what your device needs, to see the headroom.

The formula

Power = Voltage x Current       P = V x I

The fixed voltages defined for USB Power Delivery are 5 V, 9 V, 15 V, 20 V, 28 V, 36 V and 48 V, with the last three requiring cables and devices built for them. Programmable modes allow voltages in between. Which of these a link actually uses is negotiated; the calculation above applies whichever one it is.

SymbolMeaningUnit
V Negotiated voltage V
I Negotiated current A
P Power W

Worked example

A link negotiated at 20 V and 5 A:

P = 20 x 5 = 100 W

A phone charging at 9 V, 2.22 A:

P = 9 x 2.22 = 20 W

Both go through the same connector, and nothing on the outside of either cable distinguishes them.

Notes and limits

  • Above 3 A, the cable needs an identifier chip that tells the charger it can carry the current. A cable without one holds the link to 3 A however capable the charger is — which is the single commonest reason a fast charger charges slowly.
  • This page does not know which profiles your charger, cable or device support, and does not guess. Those are printed on the charger and, for the cable, frequently nowhere at all.
  • Negotiation settles on what all three ends can do. The weakest link decides.
  • USB-C also carries data and video on the same connector, and a cable adequate for one is not necessarily adequate for another.
  • Charging still slows as the battery fills, whatever the link can carry.

What this calculation assumes

  • The voltage and current are taken as entered; no Power Delivery profile is inferred.
  • What a link actually delivers is set by the charger, the cable and the device together.
  • Above 3 A, the cable must identify itself as capable or the link is held lower.

Frequently asked questions

How many watts can USB-C deliver?

Anywhere from 2.5 W to 240 W, depending on what the charger, cable and device all support. The connector itself does not determine it, which is why two identical-looking cables can behave very differently.

Why is my USB-C charger slower than its rating?

Most often the cable. Carrying more than 3 A needs a cable with an identifier chip, and one without it caps the link regardless of the charger. After that: the device not supporting the charger's profiles, a hot battery, or being above 80% charge.

What voltages does USB Power Delivery use?

The fixed ones are 5, 9, 15, 20, 28, 36 and 48 V, with the top three needing hardware built for them. Programmable modes allow values in between. Which one a link uses is negotiated between the ends.

Can I tell which profile my charger supports from its wattage?

No. Two 45 W chargers can offer different voltage and current combinations, and a device may be able to use one and not the other. The supported profiles are listed on the charger label.

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