Tools
Tools for Mac monitor shoppers.
Six small instruments we built while reviewing displays. Each one answers a question that matters specifically for macOS, in the order you run into them. Not just generic monitor math.
- Tools
- 6
- Sign-ups
- 0
- Chips
- M1–M6
01 Your Mac
Mac External Display Support
Pick your exact Apple Silicon Mac (M1 to M6). See the max external display count, per-port resolution and refresh caps, valid configurations, and the gotchas — all sourced to Apple.
02 The panel
Mac PPI Calculator & Retina Checker
Calculate pixel density for any monitor and find out if it will look Retina sharp on macOS. Live pixel grid, HiDPI scaling preview, and 218 PPI comparison.
03 The cable
Mac Cable Bandwidth Calculator
Check if your USB-C, HDMI, DisplayPort, or Thunderbolt cable can actually drive 4K 120Hz, 5K 60Hz, or 6K on your Mac. Live bandwidth pipe visualization.
04 The port
Mac Port Checker
Two USB-C ports on the same Mac can behave completely differently. Pick your Mac and see every port: which side it is on, its real data speed, whether it drives a display, runs a Thunderbolt dock, or charges the Mac.
05 The dock
Thunderbolt Dock Bandwidth Calculator
One port on the Mac, split between a display, an SSD, ethernet and USB gear. Plan the whole desk: what fits, what your chip will refuse outright, and which port each thing belongs in.
06 Your desk
Full-screen Monitor Test
Once the monitor is on your desk: dead and stuck pixels, bleed, banding, gamma, Retina scaling, P3 colour and motion. Mark what you see and keep the report for a return.
In order
When to use which tool.
The six tools solve different problems, in the order you usually run into them when picking a monitor for a Mac. Use them as a sequence, not as alternatives.
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Step 1 · Your Mac
Confirm what your Mac can drive
Apple Silicon Macs vary widely in how many external displays they support and at what resolution per port. The base M1, M2, M3 and M4 chips officially support a single external monitor, while the Pro, Max and Ultra chips raise that limit and add HDMI 2.1. The External Display Support tool shows the exact display count, per-port caps and valid configurations for your model. Check this before you shortlist a monitor.
Mac External Display Support -
Step 2 · The panel
Check whether the monitor will look Retina
macOS targets roughly 218 pixels per inch for Retina-class sharpness. That is why a 4K 27 inch panel never looks as crisp as a 5K 27 inch panel on a Mac, even though both are technically high resolution. The PPI Calculator converts any resolution and screen size into pixel density and shows how macOS HiDPI scaling will render text on that panel.
Mac PPI Calculator & Retina Checker -
Step 3 · The cable
Make sure your cable can carry the signal
Most 4K 30Hz problems are caused by cables and adapters rather than by Macs or monitors. 4K 60Hz needs around 12 Gbps, 4K 120Hz roughly 32 Gbps, and 6K 60Hz about 36 Gbps before compression. The Cable Bandwidth Calculator works out the exact bandwidth a resolution, refresh rate and bit depth require, then compares it against HDMI 2.0/2.1, DisplayPort 1.4, USB-C DP Alt Mode, and Thunderbolt 3, 4 or 5.
Mac Cable Bandwidth Calculator -
Step 4 · The port
Work out which port to actually plug it into
USB-C is a connector shape, not a capability. On a lot of Macs some USB-C ports are full Thunderbolt while others are plain USB with no video output at all — the Mac Studio, the Mac mini M4, the four-port iMacs and the MacBook Neo all do this, and nothing on the chassis tells them apart. The Port Checker shows every port on your model, which side it is on, how fast it really is, and whether it will drive a display, run a Thunderbolt dock, or charge the Mac.
Mac Port Checker -
Step 5 · The dock
Work out what happens when everything shares one port
A dock takes that one port and splits it between a display, an SSD, ethernet and USB gear. Everything behind the dock shares a single link, and that link is really two separate one-way pipes, not one pool. This is why plugging in a monitor can halve your SSD write speed while read speed stays the same. The Dock Bandwidth Calculator works out the budget for each direction, applies your chip’s own display ceiling, marks the ports that cannot run a dock at all, and works out which port every device should be in.
Thunderbolt Dock Bandwidth Calculator -
Step 6 · Your desk
Test the monitor the day it arrives
Panel defects are easiest to return while the box is still in the hallway. The Full-screen Monitor Test runs dead pixel, bleed, banding, gamma, scaling, colour and motion checks in physical pixels. It classifies any pixels you mark and gives you a report you can paste into a return request.
Full-screen Monitor Test
FAQ
Frequently asked questions.
Are these Mac monitor tools free?
Yes, 100%. Every tool on RetinaDesk is free. They run entirely in your browser and do not require an account. There are no usage limits, no signups, and no data leaves your device.
Which tool should I use first when picking a monitor for my Mac?
Start with the External Display Support tool to confirm how many monitors your specific Mac can drive and at what resolution per port. Then use the PPI Calculator to check whether a candidate monitor will look Retina-sharp at your seating distance. Finally, run the Cable Bandwidth Calculator to make sure your existing cable can actually carry that resolution and refresh rate without dropping to 30Hz. Once everything is on your desk, the Port Checker tells you which physical port to plug it all into.
What is the difference between the Port Checker and External Display Support?
They answer adjacent questions and are designed to be used together. External Display Support is about display bandwidth: how many monitors your chip can drive, at what resolution, and in which combinations. The Port Checker is about the physical layer: where each port is on the chassis, how fast it runs for data, whether it charges the Mac, and whether it will run a Thunderbolt dock. Port capability tells you where to plug in; display support tells you what you get once you do.
Do these tools work for Intel Macs as well as Apple Silicon?
The PPI Calculator and Cable Bandwidth Calculator are model agnostic and work for any Mac, including Intel models. The External Display Support tool is scoped to Apple Silicon Macs (M1 through M6) because port and display behaviour changed substantially with the Apple Silicon transition and the data is curated against Apple’s current official specifications.
Why focus on macOS instead of generic monitor calculators?
macOS treats displays differently from Windows and Linux: HiDPI scaling, the 218 PPI Retina reference, DisplayPort tunnelling over Thunderbolt, and per chip display limits all matter when picking a monitor for a Mac. Generic calculators ignore these constraints. A lot of people end up with monitors that technically work but never look right on macOS.
How often is the data behind these tools updated?
The display support data is refreshed when Apple ships a new chip generation or updates the specs of an existing model. Cable and bandwidth standards are stable, but the calculator is updated when new standards such as Thunderbolt 5 or DisplayPort 2.1 UHBR 20 reach the Mac lineup.
Once you have your answer.
Tools narrow the specs. The rest of RetinaDesk picks a monitor.