WhatCable Reports on USB-C Cable Power and Speed

[ace (Adam Engst)]

Originally published at: WhatCable Reports on USB-C Cable Power and Speed - TidBITS

Most of us probably have a collection of random USB-C cables that have arrived over the years with various devices and peripherals or were purchased quickly as needed. Apart from the difference between smooth and braided cables and the colors—most of mine are either white or black—they’re nearly impossible to tell apart. Someone who is more obsessive than I might have labeled them when they arrived, but I suspect most people just toss them in a drawer, box, or bag. I’ll show you mine if you show me yours (yes, I still keep some things in 3.5-inch floppy boxes).

But not all USB-C cables are created equal. Even beyond the difference between Thunderbolt and USB, USB-C cables can support a wide variety of power and bandwidth specs. For instance, Apple is notorious for shipping “charge-only” cables that support data only at slow USB 2.0 speeds of 480 Mbps. And there’s no way to know at a glance what the random cable that shipped alongside some device can do.

Hardware testers exist—some of my Apple Consultants Network friends carry this Treedix USB Cable Tester—but for most people, they’re overkill. Instead, download the WhatCable app, which gives you a vast amount of information about your cables for free. A paid WhatCable Pro tier ($13.99/£9.99) lets you name cables and shows what each port, cable, and device combination can do and has negotiated.

Using WhatCable is trivially easy—you just launch the app and scroll through its reports on each cable/device that’s attached via USB-C. It shows you the port in use, a headline (“Thunderbolt / USB4 • 3W charger” in this case), a brief description of what the cable can do, and boxed summaries of the cable’s capabilities for charging, throughput, and display quality. After that, it lists all the details it can discern about the cable and what it knows about the connected devices (an Apple Studio Display in this case). If you’re a glutton for technical punishment (“please sir, more specs!”), click the Show Technical Details switch at the bottom.

Those Apple “charge-only” cables? They look a lot different in WhatCable, as you can see from this one connecting my iPhone 17 to my Mac. You really don’t want to use one of these cables to connect an external SSD.

In this case, it doesn’t matter what cable I use because the iPhone 17 itself is limited to 480 Mbps. That became obvious when I switched to my go-to OWC Thunderbolt 4 cable. Even though WhatCable correctly identifies it as a Thunderbolt cable capable of 40 Gbps, the app notes that only USB 2.0 is active because of the iPhone 17’s limitations.

It was also illustrative to plug in an Anker USB-C hub with several USB-A ports and then attach an old OWC hard drive that turned out to be limited to USB 2.0’s 480 Mbps and a SanDisk flash drive that supported USB 3.0’s 5 Gbps. I wouldn’t have guessed the hard drive was that slow just from looking at it.

I could keep working my way through the rat’s nest of USB-C cables in that bag, but you get the idea. WhatCable also includes macOS widgets so you can see what’s connected at a glance and can trigger notifications when cables connect or disconnect. You can choose between a normal windowed app or a menu bar popover, and Terminal wonks can even run it at the command line.

As long as you’re running macOS 14 Sonoma or later on a Mac with Apple silicon (Intel-based Macs are out of luck), I encourage you to download WhatCable 1.4 today and take a spin through its documentation for more details. If you regularly work with many USB-C cables, consider WhatCable Pro for its additional identification and diagnostic capabilities.

[Shamino (David C.)]

@ace

I’ll show you mine if you show me yours (yes, I still keep some things in 3.5-inch floppy boxes).

Since you asked. My parts closet is pretty well organized, but there are still a ton of random cables:

[Simon]

@ace

Someone who is more obsessive than I might have labeled them when they arrived, but I suspect most people just toss them in a drawer, box, or bag.

I do indeed label my cables (and adapters) when I obtain them if they’re made for higher wattage (100W or 240W) or higher throughput (40 Gbps) to distinguish them from just any old USB-C cable. The latter I readily throw out if it doesn’t serve a specific purpose or is very well manufactured. The former I tend to keep around. I will always end up needing a good TB4 cable for something.

Instead, download the WhatCable app, which gives you a vast amount of information about your cables for free.

That is indeed a neat app. I have a cable meter, but it’s still nice to have an app that can tell you something about what’s connected right now rather than first having to plug it in, as when I use the meter.

Seeing though, how this app has been done, it does strike me that, in principle, this is the kind of information Apple should be supplying via System Information. That thing does a good job at displaying the high-level information everyday Joes need in a fairly succinct form at the top level, while then offering detailed drill-downs with details for the nerds. Such a TB or USB drill-down is where this kind of detail ought to be displayed for us nerds to go obsess about. But heck, if Apple doesn’t want to do it, cheers to Bitmoor for offering it up in such a simple and nice package (and with great online documentation!). And even for free!

[mschmitt (Michael Schmitt)]

@ace

Someone who is more obsessive than I might have labeled them when they arrived, but I suspect most people just toss them in a drawer, box, or bag.

What’s annoying is having to re-label old cables every time a new USB version is released.

---

If you don’t get the joke, it is because starting in 2015, the USB Implementers Forum retroactively renames old standards when a new standard is released. For example:

• 2015: USB 3.1 is released. USB 3.0 is now “USB 3.1 Gen 1”, the actual USB 3.1 is “USB 3.1 Gen 2”.
• 2019: USB 3.2 is released as “USB 3.2 Gen 2x2”. USB 3.0 (aka USB 3.1 Gen 1) is now USB 3.2 Gen 1, USB 3.1 (USB 3.1 Gen 2) is now “USB 3.2 Gen 2”.
• They retroactively changed USB twice more after this

[Shamino (David C.)]

@mschmitt

They retroactively changed USB twice more after this

All of those terms are completely deprecated. The USB forum actively discourages all use of the standard’s version numbers for product labeling, precisely because of all the confusion.

Like most industry standards, new revisions include all content from the old revisions, but they do not mandate support for the latest and greatest features.

So a basic 480 Mbps cable can be advertised as “USB3” or “USB3.2” or “USB4” or in the future “USB289123”, because all those newer standards include the old specs.

The USB Implementer’s Forum want product manufacturers to advertise the data-rates and other capabilities (e.g., power-delivery capacity), without regard to any specific version of the standard.

And data-rates should be marketed as the actual bit-rates, although the marketing buzzwords used in the past are still considered applicable. The data rates are:

• low speed. The original 1.5 Mbit/s data rate
• full speed. The 12 Mbit/s data rate, also from the original standard
• high speed. 480 Mbit/s. Introduced in USB 2.0.
• super speed. 5 Gbit/s. Incorrectly called USB 3.0 by many
  • I say “incorrectly”, not only because of the USB Implementers Forum request, but because I’ve seen plenty of 480 Mbit/s cables advertised as “USB 3.0”. technically correct, but massively misleading.
• Faster cables and interfaces don’t have standard buzzwords, but should be marketed as 10Mbps, 20Mbps, 40Mbps, etc.

[schwartz (Dana Schwartz)]

Come on, today is not April 1st!

[AlanRalph]

I installed WhatCable the other day, and was relieved to see that my current cabling and hub are delivering maximum throughput to those devices that need it. One oddity was that my large vertical mouse is apparently ‘high-speed’, not sure if that’s to support faster response rate, I don’t recall it being advertised as such.

I have just the one box of spare USB cables now, as I’ve gone through and disposed of ones that no longer fit or work with anything I own. Unfortunately, I needed to invest in several extra cables and adapters when I got my 2024 M3 MacBook Air so I could connect stuff to its two USB-C / Thunderbolt ports. I did make a point of double-checking the USB ratings for each item!

I have two charging-only ports on the hub I’m using, those are reserved for charging my iPhone and an old Kindle I keep around.

[josehill]

@AlanRalph

One oddity was that my large vertical mouse is apparently ‘high-speed’, not sure if that’s to support faster response rate, I don’t recall it being advertised as such.

My guess is manufacturers have reached the point where the price and availability differences between “high speed” and lower speed interfaces has become negligible.

[leipziger1492]

Just reading the newsletter today and realized that I’d installed WhatCable about a month ago after John Gruber (I think it was John, or else Michael Tsai) mentioned on their blog. These are the kind of utilities we need to have.

Fortunately, I do NOT still have any SCSI cables

[jdowns (John Downs)]

iPhone data transfer is limited to 480 Mbps? What-the-what? Why?

[Simon]

@jdowns

iPhone data transfer is limited to 480 Mbps? What-the-what? Why?

Yes. Unless you have an iPhone 15 Pro or newer Pro/Max model, your iPhone is stuck at old USB2, i.e. 480 Mbps max throughput (what they call Hi-Speed right now — until they for the 38th time rename the standard again, probably in 3-4 weeks from now).

Yes, you read that right. In 2026, an $800 boutique smartphone from the world’s biggest computer company is stuck doing all its wired transfers at speeds dictated by a standard that was released way back in April of 2000, note, that was a time before Putin took office. That’s how long ago that was.

It’s an utter embarrassment.

But there is light at the end of the tunnel!

Apple recently introduced ads in Maps and they offer no opt-out anywhere. Not even for those who pay them twice via iCloud+. Initially, you might have thought this was because they were going to give us all a big fat juicy discount on new iPhones. But turns out, that was instead intended to collect the pennies it takes to upgrade the regular iPhone from a 480-Mbps standard from 26 years ago to a 5-Gbps standard from 18 years ago (well, not for this year’s 18 [rumored to be a more expensive rehash of last year’s 17], but next year’s 19 perhaps). Now cowardly cynics may ridicule them for that, but heck, it sure beats passing a hat around. People finally need to show some love for this struggling beleaguered company. Those dividend checks don’t write themselves. Compassion!

[jdowns (John Downs)]

That’s absurd. What’s the max data transfer rate on the Pro/Max models?

[Simon]

@jdowns

That’s absurd. What’s the max data transfer rate on the Pro/Max models?

10 Gbps USB3 (what they now recently called “SuperSpeed”)

[Shamino (David C.)]

The “SuperSpeed” buzzword was introduced for 5 Gbps.

There was, briefly, a “SuperSpeed+” buzzword for the 10 and 20 Gbps speeds. These logos included the speed as a part of the image.

But both are deprecated. Current branding should simply say “5 Gbps”, “10 Gbps” and “20 Gbps” and not use any buzzword.

[khoi (Khoi Vinh)]

WhatCable looks very handy. Thank you for spotlighting it! I’ve actually been considering a hardware cable tester recently because I never know when a cable has gone bad or there’s some other issue happening. This is a recurring situation in my car, where we seem to have to switch out USB cables for CarPlay every six months or so. Does WhatCable help diagnose broken cables?

[Shamino (David C.)]

@khoi

This is a recurring situation in my car, where we seem to have to switch out USB cables for CarPlay every six months or so.

Have the car’s USB port checked. On my wife’s car (2018 Kia Sedona), the USB port got massively flaky over the years. It initially manifested as intermittent CarPlay failures, but now it simply doesn’t work at all.

Unfortunately, the dealer was no help trying to fix this.

I’d probably open up the panel, remove the cable, and solder a new/better socket to the pins. But my wife doesn’t want me to do it, so CarPlay is pretty much dead on that car. (We stream audio from her phone via BlueTooth, or from my iPod via the AUX line-in jack.)

[AlanRalph]

@leipziger1492

Fortunately, I do NOT still have any SCSI cables

Yikes, I remember that PITA from the 1990s and 2000s! Back then, SCSI was still very much a thing, particularly for tape drives but also for some CD-ROM and CD-R(W) drives as well. Having to use jumpers to set device number and/or termination on each drive is something I have no desire to every return to.

Our occasional USB transfer speed mysteries pale by comparison, IMHO.

[josehill]

@AlanRalph

I remember that PITA from the 1990s and 2000s! Back then, SCSI was still very much a thing

That triggered my memory of two custom-manufactured 50-foot differential SCSI cables that I commissioned back in 1996. For data center space reasons, it was impractical to place a large RAID unit next to the intended server, but the differential SCSI specification allowed cables up to 25 meters long. Those probably were the best constructed cables I’ve ever seen, and they weighed…a lot! I wish I could remember how much they cost.

[nello]

@leipziger1492

Just reading the newsletter today and realized that I’d installed WhatCable about a month ago after John Gruber (I think it was John, or else Michael Tsai) mentioned on their blog.

Perhaps you installed WhatCable after reading my July post:

Cable Testing

Does anyone recommend software that tests USB and Thunderbolt cables? Is any software a good substitute for a hardware cable tester? Has anyone used WhatCable? @glennf UPDATE Tuesday, August 25, 2026 2:18 AM (UTC) For a review of WhatCable, see: