USB-C Cable Ratings Explained: e-marker, 3A vs 5A, USB2 vs USB3.2 vs Thunderbolt
A cable's charging speed depends on its amperage rating (3A or 5A) and, above 60W, whether it has an "e-marker" chip — its data speed (USB2, USB3.2, Thunderbolt/USB4) is a completely separate spec.
What is an e-marker?
An e-marker (short for "electronically marked cable") is a small chip embedded in a USB-C cable's connector that identifies the cable's rated current and capabilities to the devices on either end. The USB-C spec requires an e-marker for any cable carrying more than 3A (i.e. more than 60W at 20V) — without it, a charger and device will refuse to negotiate above the safe 3A default, no matter how thick the cable actually is inside. Cables marketed as "100W" or "240W" are e-marked; a plain unlabeled USB-C cable almost certainly isn't.
3A vs 5A cables
Every compliant USB-C cable supports at least 3A (60W at 20V), which is enough for the large majority of phones and tablets. 5A e-marked cables unlock up to 100W (or 240W with USB PD 3.1 EPR support on both ends) and matter mainly for laptops and a handful of very fast-charging phones. Using a 3A cable with a 65W+ charger and a laptop that needs 65W+ won't damage anything — it will simply charge slower than the charger and laptop are capable of.
USB2 vs USB3.2 vs Thunderbolt/USB4 — data speed, not charging speed
This is the part that trips people up: a cable's data speed rating is unrelated to its charging wattage rating. USB 2.0 tops out at 480Mbps and is what most bundled charging cables use — perfectly fine for charging, slow for transferring files. USB 3.2 Gen 1/Gen 2 cables reach 5-10Gbps. Thunderbolt 3/4 and USB4 cables reach up to 40Gbps and also tend to support the highest charging wattages, but that's a marketing bundling choice, not a technical requirement — a cable does not need fast data lines to carry high current.
Quick reference
| Rating | Max charging wattage | Needs e-marker? | Typical data speed |
|---|---|---|---|
| Unmarked / basic | ~60W (3A) | No | USB 2.0 (480Mbps) |
| "100W" e-marked | 100W (5A) | Yes | Usually USB 2.0, sometimes USB 3.2 |
| USB4 / Thunderbolt | Up to 240W (5A, PD 3.1 EPR) | Yes | Up to 40Gbps |
| Proprietary (VOOC/Warp/HyperCharge/SuperCharge) | Brand-specific, up to 240W | No — own cable spec | Usually USB 2.0 |
How to tell what you have
Look for wattage or amperage printed directly on the cable connector or its packaging ("100W", "5A", "3A"). No markings at all is a strong hint it's a basic 3A/60W cable. If you're trying to fast-charge a laptop or a phone rated above 60W and it isn't reaching full speed, the cable is one of the first things worth checking — run your exact combination through the FastChargeCheck calculator to see the cable requirement for your specific device and charger.
Frequently asked questions
- Can I just use any USB-C cable for fast charging?
- Only up to 60W. Above that, the cable must be 5A e-marked, or it will cap charging speed regardless of what the phone and charger support.
- Does a thicker cable charge faster?
- Not by itself — thickness (gauge) affects how much current a cable can safely carry, but what actually determines the charging speed is the cable's rated amperage and, above 60W, whether it has an e-marker chip.
- Is a fast-charging cable also a fast data-transfer cable?
- Not necessarily. Charging wattage and data speed are independent specs — a cable can be rated for 100W charging and still only do USB 2.0-speed (480Mbps) data transfer.