Mac Cable Bandwidth Calculator — HDMI, DisplayPort & Thunderbolt

How to read a bandwidth number

A monitor needs a steady stream of data to show an image. How much data? It comes down to a few simple things. The screen’s width, height, refresh rate, and how much color detail each pixel has. Multiply those together add a bit of extra for timing. Finally you can get the total bandwidth needed.

For example, a 5K display at 60Hz with 10-bit color needs roughly 28 Gbps.

Now here’s the most important part. Every cable and port has a limit. If your setup needs more bandwidth than the cable can handle then something has to give. The display might drop to a lower refresh rate and reduce color quality or fail to connect properly.

Also, don’t be fooled by marketing numbers. There’s a difference between “raw speed” and what you actually get. HDMI 2.0 says 18 Gbps but in reality you get about 14.4 Gbps. DisplayPort 1.4 says 32.4 Gbps, but usable is about 25.9 Gbps.

Newer standards like HDMI 2.1 and DisplayPort 2.1 are more efficient. And their real world numbers are closer to what’s advertised. What actually matters is the usable bandwidth. Because that’s what your monitor is going to receive.

HDMI on Mac: FRL, TMDS, and the 2.1 gap

HDMI 2.0 uses an older system called TMDS. It tops out at 4K 60Hz with basic 8-bit color. And that limit is hard. There’s no compression support and you can’t push it further.

HDMI 2.1 is a big upgrade. It switches to a newer system called FRL and increases bandwidth significantly. More importantly, it supports DSC compression. And it makes things like 4K 240Hz or 8K 60Hz possible.

On Macs, this matters a lot. Newer MacBook Pros with M2 Pro and later have real HDMI 2.1 ports. While some older macs like M1 Pro and M1 Max are limited to HDMI 2.0.

If you’re using an older Mac and want higher performance over HDMI then your best bet is to go through USB-C or Thunderbolt with a good adapter that supports compression. Cheap adapters are often the reason a 4K display gets stuck at 30Hz.

USB-C, DisplayPort Alt Mode, and HBR3

Every Apple Silicon Mac supports DisplayPort through USB-C using something called Alt Mode.

In simple terms, this gives you enough bandwidth for 4K at 120Hz, 5K at 60Hz, and even 6K at 60Hz when compression is used.

One of the easiest and most reliable setups is a simple USB-C to DisplayPort cable. It avoids the unpredictability of HDMI adapters and technically just works.

Thunderbolt 3, 4, and 5 on Apple Silicon

Thunderbolt 3 and Thunderbolt 4 are basically the same when it comes to displays. Both carry DisplayPort 1.4 internally and the actual display performance is also identical.

Thunderbolt 4 is more about reliability and standards. And alos not about speed.

Thunderbolt 5 is where things really change. It offers much higher bandwidth. It also supports multiple high resolution displays and enables newer DisplayPort 2.1 features.

This is what makes setups like dual 6K displays or even 8K without compression possible.

Why your 4K monitor is stuck at 30Hz

In most cases, it’s not your monitor or your Mac. It’s the cable or adapter.

4K at 60Hz needs more bandwidth than older HDMI cables can handle. If you’re using an HDMI 1.4 cable or a cheap USB-C to HDMI adapter then you’ll likely be limited to 30Hz.

Your Mac will automatically choose the best option the cable can support. So if it’s stuck at 30Hz then that’s usually the bottleneck.

The fix is really simple. Just use a proper HDMI 2.0 or 2.1 cable and replace the low quality adapters. Or switch to USB-C to DisplayPort.

That last option is often the most reliable way to avoid these kinds problems completely.

DSC on Mac: the compression that makes 6K possible

Display Stream Compression (DSC) is what makes the modern high resolution displays practical. It compresses the video signal in a way that looks identical to the human eye.

This is how a single cable can drive a 6K display and how the Apple Studio Display runs at 5K 60Hz with full color.

All Apple Silicon Macs support DSC. Even the base M1 support it.

But there’s one important limitation. HDMI 2.0 doesn’t support it. That means HDMI 2.0 is truly capped at 4K 60Hz with basic color.

When your Mac, cable, and monitor supports DSC then you get higher resolutions and refresh rates without any visible loss in quality.

Frequently asked questions

Why is my 4K monitor only running at 30Hz on my Mac?

Almost always a cable or adapter problem. 4K 60Hz needs roughly 12 Gbps of payload bandwidth. A cheap USB-C to HDMI adapter that internally speaks HDMI 1.4 will cap you at 4K 30Hz even if the monitor and Mac can do more. Replace it with a certified HDMI 2.0 or 2.1 cable, or switch to a USB-C to DisplayPort cable, which every Apple Silicon Mac supports natively.

Can M1, M2, M3, or M4 MacBooks do 4K 120Hz over HDMI?

Yes from M2 Pro onward, using the built-in HDMI port. The January 2023 MacBook Pro with M2 Pro or M2 Max was the first Mac with HDMI 2.1, and every Pro, Max, and Ultra chip since has kept it. M1 Pro and M1 Max MacBook Pros have HDMI 2.0, which caps at 4K 60Hz. You can still reach 4K 120Hz on an M1 Pro or M1 Max by going through a Thunderbolt port with a USB-C to DisplayPort cable, because DP 1.4 with DSC has the bandwidth.

Does USB-C to DisplayPort work on MacBook Pro?

Yes. Every USB-C and Thunderbolt port on an Apple Silicon Mac supports DisplayPort Alt Mode at HBR3. That gives you about 25.92 Gbps of effective bandwidth, enough for 4K 120Hz, 5K 60Hz, and 6K 60Hz when the monitor supports DSC. A passive USB-C to DP 1.4 cable is the simplest and most reliable way to drive a high-resolution display on any Apple Silicon Mac.

What is the difference between Thunderbolt 3, 4, and 5?

Thunderbolt 3 and Thunderbolt 4 both run at 40 Gbps total. For displays, they tunnel DisplayPort 1.4, which gives about 25.92 Gbps of effective payload. Thunderbolt 5 doubles the base to 80 Gbps symmetric and can push 120 Gbps asymmetric toward a display. It tunnels DisplayPort 2.1 UHBR 20, meaning roughly 77.37 Gbps of usable display bandwidth. Practically: TB3 and TB4 reach 6K 60Hz with DSC, while TB5 handles 6K 120Hz or dual 6K without compression.

Does my Mac support HDMI 2.1?

Built-in HDMI 2.1 arrived with the M2 Pro and M2 Max MacBook Pro in January 2023. Every Pro, Max, and Ultra chip since (M2 Ultra, M3 Pro, M3 Max, M3 Ultra, M4, M4 Pro, M4 Max) has it on the chassis. M1 Pro and M1 Max MacBook Pros still have HDMI 2.0 (4K 60Hz max). M1 and M2 base MacBook Airs and MacBook Pro 13 have no built-in HDMI at all. Any Mac can still reach HDMI 2.1 speeds via a USB-C or Thunderbolt port using a quality adapter, preferably one based on the VMM7100 chipset.

Can a single cable do 5K 60Hz on a Mac?

5K 60Hz at 10-bit color needs about 28 Gbps of payload bandwidth. DisplayPort 1.4 with DSC comfortably carries that over a single cable, which is why Apple ships a single Thunderbolt cable with the Studio Display. A passive USB-C to DP 1.4 cable will also do it, as will any Thunderbolt 3, 4, or 5 cable.

Does Mac support Display Stream Compression (DSC)?

Yes, across the entire Apple Silicon lineup. Even the base M1 MacBook Air can drive a Pro Display XDR at 6K 60Hz, which only fits over one DisplayPort link with DSC in play. DSC is what lets 6K 60Hz work on Thunderbolt 3 and 4, what lets 4K 240Hz work over HDMI 2.1, and what lets 8K 60Hz fit on cables that would otherwise be too narrow. It is visually lossless in nearly all cases. DSC does not apply to HDMI 2.0 though. TMDS signalling has no DSC provision, so an HDMI 2.0 link is hard-capped at 4K 60Hz 8-bit.

Do I need a Thunderbolt 5 cable for the M4 Pro Mac mini?

Only if you want to run a display that genuinely needs more than DP 1.4 can carry. A single 4K, 5K, or 6K monitor at 60Hz is fine on a normal Thunderbolt 4 cable, because the display data tunnels over DP 1.4 with DSC. Thunderbolt 5 cables matter for 6K at high refresh, dual 6K, 8K, or when you are pairing the Mac with a TB5 dock or external GPU.