Fix an external monitor that's at the wrong resolution on your Mac

Why it happens

Your Mac picks a resolution it thinks suits the monitor, and it doesn't always choose the full one. Some adapters and older HDMI cables can't carry 4K or very wide pictures, so the best sizes never appear. Hubs and docks can limit what reaches the monitor too.

How to fix it

1. Look up your monitor's native resolution on its box, label or maker's website. Common ones are 2560 × 1440, 3440 × 1440 for an ultrawide, and 3840 × 2160 for 4K.

2. Open the Apple menu, choose System Settings and click Displays. If you have more than one screen, click the external monitor at the top first.

3. If you only see a row of size pictures, Control-click them and choose Show List. Then turn on Show all resolutions and pick the native resolution.

   Displays›Resolution›Show all resolutions

4. When your Mac asks you to confirm the new display setting, click Confirm. If you click Revert, or wait 15 seconds, it goes back to the old setting.

5. On a 4K monitor, your Mac often picks a scaled size with bigger text. It still uses every pixel, so it stays sharp. Choose a size with more space if you want more room on screen.

Still not fixed?

1. Native size missing? Swap the cable or adapter. Use a certified high-speed HDMI cable, a DisplayPort cable, or a USB-C or Thunderbolt cable that carries video.

2. Plug the monitor straight into your Mac instead of a hub or dock, and try another port on the Mac.

3. Picture doesn't fill the screen, or the edges are cut off? Use the monitor's own buttons to check its input and set its picture size to an option like 1:1 or Just Scan.

4. Install any waiting update in General > Software Update. Support for new monitors often improves in updates.

   General›Software Update

5. If the native resolution is still missing with a good cable and a direct connection, try the monitor with another computer. If it fails there too, contact the monitor's maker. If only your Mac can't show it, contact Apple Support.