USB-C cables explained: which cable will charge a laptop (60 W vs 100 W vs 240 W)?
You have a drawer full of USB-C cables. One charges the laptop at full speed, another makes it say “slow charger”, and a third won't drive the monitor at all. The plugs are identical; the wires inside aren't.
The three things a USB-C cable can differ in
| What | Options | What it means for you |
|---|---|---|
| Power | 3 A (up to 60 W) · 5 A e-marked (up to 100 W) · 5 A EPR (up to 240 W) | Phones and tablets need far less than 60 W. Laptops rated 65–100 W need a 5 A cable to charge at full speed; 140–240 W laptops need an EPR (240 W) cable. |
| Data speed | USB 2.0 (480 Mbit/s) · USB 3.x (5, 10 or 20 Gbit/s) · USB4 / Thunderbolt 3, 4, 5 (20–80 Gbit/s) | Only matters for drives, docks and displays. Most cables sold “for charging” are USB 2.0. |
| Video | None (USB 2.0 cables) · DisplayPort over USB-C (USB 3 and up) | A monitor over USB-C needs a full-featured cable and a port that supports video. |
A small chip in the plug, the e-marker, tells the charger the cable can safely carry 5 A. Without it, chargers stop at 3 A even if the cable is thick. That's deliberate: too much current through a thin cable gets hot.
Why a laptop says “slow charger” with the wrong cable
A 100 W charger talking to a laptop through a plain 3 A cable will cap itself at 60 W. A laptop that wants 90 W then charges slowly, or only holds its level while you work, and some show a warning. Swap to a cable printed or labelled 100 W, 5 A or 240 W. Watts are volts times amps: 20 V × 3 A = 60 W, 20 V × 5 A = 100 W, 48 V × 5 A = 240 W.
It works the other way too: a 240 W cable is perfectly safe with a 20 W phone charger. The charger and the device agree on the power; the cable only sets the upper limit.
How to tell which cable you have
- Look at the plug or the packaging. Newer certified cables carry a logo with the wattage (60 W or 240 W) and sometimes the speed (for example 40 Gbps). Thunderbolt cables have a lightning-bolt symbol.
- Thin and cheap, came free with a phone: usually 3 A, USB 2.0. Fine for charging phones; no video.
- Very short and thick, with a bolt or “USB4” mark: high-speed data and video. Long full-speed cables (over about 1 m) are often “active” and pricier.
- Test it: many laptops show the charging wattage (on a Mac, hold Option and click the Apple menu, then System Information, Power; on Windows, some maker apps show the adapter wattage). A cheap inline USB-C power meter shows volts, amps and watts.
USB-A to USB-C and other adapters
A USB-A to USB-C cable can only carry what the old USB-A port gives, typically 5–18 W (higher only with proprietary fast-charge standards). It won't charge most laptops. Avoid cheap A-to-C cables without the correct resistor inside; they can ask a charger for more than it should give. Lightning-to-USB-C cables carry USB Power Delivery and fast-charge an iPhone with a 20 W or larger USB-C charger.
Quick picks
| Job | Cable |
|---|---|
| Phone, earbuds, watch, power bank | Any decent USB-C cable (3 A) |
| Laptop up to 60 W | Any USB-C to USB-C cable |
| Laptop 65–100 W | 5 A / 100 W e-marked cable |
| Laptop 140–240 W | 240 W (EPR) cable |
| Monitor, dock, fast SSD | USB 3.2, USB4 or Thunderbolt cable, and check the port supports it |
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Questions
Can any USB-C cable charge a laptop?
Any proper USB-C to USB-C cable carries up to 60 watts, which is enough for many small laptops. Laptops that need 65 to 100 watts need a 5 amp e-marked cable to charge at full speed, and 140 to 240 watt laptops need a 240 watt cable.
What is an e-marked USB-C cable?
A cable with a small chip in the plug that tells the charger how much current it can safely carry and how fast it is. Chargers only supply more than 3 amps when they see that chip.
Is it safe to use a 240 W cable with a phone charger?
Yes. The charger and the phone agree on how much power to use; the cable only sets the maximum. A higher-rated cable never forces extra power into a device.
Why won't my USB-C cable work with my monitor?
Many USB-C cables, especially ones that came with phones, only carry USB 2.0 data, which has no room for a video signal. You need a USB 3, USB4 or Thunderbolt cable, and the laptop port must support video output.
Is a Thunderbolt cable the same as USB-C?
Thunderbolt 3, 4 and 5 use the USB-C plug, and a Thunderbolt cable works as a high-quality USB-C cable for charging and data. A plain USB-C cable may not work for Thunderbolt devices.
Published · updated .