What you need to check first

Before you buy a second monitor or dig through cables, look at the back of your computer. You need at least two video ports — the places where monitor cables plug in. Most computers have them, but older machines or laptops might have only one. The ports you are looking for are HDMI (the flat rectangular one), DisplayPort (smaller and rectangular), DVI (has two rows of pins), or VGA (the one with three rows of holes). A single computer can mix different port types — you do not need two identical ones.

If your computer has only one video port and no USB-C or Thunderbolt port, you will need a USB video adapter to add a second display. These are inexpensive and plug into any USB port on your computer, then connect to your second monitor. They work, but they use more of your computer's processing power than a direct video port would.

Laptops are trickier. Many modern laptops can output video through USB-C or Thunderbolt, even if they have no traditional monitor port. Check your laptop's manual or the manufacturer's website to see what video outputs it supports.

Key Takeaways

  • Most desktop computers have at least two video ports on the back, but you should check yours before buying a second monitor.
  • HDMI and DisplayPort are the most common ports on newer computers; older machines may have DVI or VGA instead.
  • If your computer has only one video port, a USB video adapter can add a second display without opening the computer.
  • After plugging in both monitors, your operating system will detect them automatically and let you arrange them in settings.
  • You can extend your desktop across both screens or mirror the same image on both, depending on what you are doing.

Connecting the monitors to your computer

Plug the first monitor into one video port on the back of your computer using the appropriate cable. Plug the second monitor into a different video port. If you are using a USB video adapter, plug the adapter into a USB port instead, then connect the second monitor's cable to the adapter. Turn on both monitors and your computer.

Your operating system should detect both monitors within a few seconds. If it does not, restart your computer. If one monitor still does not show up after a restart, try a different video port or a different cable — the port or cable may be faulty.

Setting up your displays in Windows

Right-click on your desktop and select Display settings. You will see a diagram showing both monitors. Windows labels them 1 and 2 and shows which one is currently your main display (the one with the Windows taskbar).

Drag the monitor boxes in the diagram to match how your physical monitors are arranged. If your second monitor is to the right of your first one, drag it to the right in the diagram. If it is above, drag it up. This arrangement tells Windows how to move your cursor and windows between screens — if you do not match the diagram to your physical setup, moving your mouse to the right might make it jump to the left side of the other monitor instead.

Below the diagram, you can choose whether to extend your display (use both screens as one large workspace) or mirror it (show the same thing on both). Most people choose extend. You can also choose which monitor is your main display — the one where new windows and dialog boxes open by default.

Setting up your displays on a Mac

Click the Apple menu and go to System Settings, then Displays. Your Mac will show both monitors. Click Arrangement to see a diagram of your displays and drag them to match your physical setup, just as you would in Windows.

In the same Displays settings, you can choose your main display (the one with the menu bar) and decide whether to extend or mirror. Macs default to extending, which is what most people want. If you are using an older Mac with an external GPU or special video hardware, you may need to restart after connecting a second monitor.

Troubleshooting a monitor that will not show up

If you plugged in a second monitor and your computer does not detect it, try these steps in order. First, unplug the monitor cable from the computer and plug it back in firmly. Second, restart your computer. Third, try a different video port on your computer — one port may be disabled or broken. Fourth, try a different cable if you have one available.

If you are using a USB video adapter, make sure it is plugged into a USB 3.0 port (usually blue inside) rather than an older USB 2.0 port. USB 2.0 does not have enough bandwidth for video. If your computer still does not detect the second monitor after trying all of these, the video port, the cable, or the monitor itself may be faulty.

On Windows, you can also try right-clicking your desktop, selecting Display settings, scrolling down, and clicking Detect. This forces Windows to scan for monitors again. On a Mac, hold down the Option key, click the Apple menu, and select System Information, then Graphics/Displays to see what video outputs your Mac recognizes.

Using both screens for different tasks

Once both monitors are set up and arranged, you can drag windows between them by clicking and holding the title bar of a window and dragging it to the other screen. Most people use one monitor for their main work and the other for reference material, chat, or video calls. You can also make a window full-screen on one monitor without affecting the other.

If you want a program to always open on a specific monitor, drag its window to that monitor, then close the program. When you open it again, it will usually remember which monitor you used last. Some programs have their own settings for which display to use — check the program's preferences if you need more control.

Frequently Asked Questions

Can I use two monitors with different resolutions?

Yes. Windows and macOS handle different resolutions automatically. One monitor might be 1920 by 1080 and the other 2560 by 1440, and both will work fine. Your cursor will move smoothly between them, and windows will resize correctly when you drag them across.

Do I need special cables or adapters?

Only if your computer does not have two video ports. If it has two HDMI ports, two DisplayPort ports, or one of each, you just need the cables that came with your monitors. If your computer has only one port, a USB video adapter is the simplest solution and costs between $20 and $60.

Will connecting two monitors slow down my computer?

Not noticeably, unless you are using a USB video adapter on an older computer. Direct video ports have almost no impact on performance. USB adapters use a small amount of CPU power, but most modern computers handle it without any slowdown you would notice during everyday work.

Can I connect three or more monitors?

Yes, if your computer has enough video ports or USB ports. Many graphics cards have three or four video outputs. If your computer does not have enough ports, you can add more with additional USB video adapters, though performance may suffer if you use too many at once.

What if my monitor cable does not match my computer's port?

You need an adapter. HDMI to DisplayPort adapters, DVI to HDMI adapters, and VGA to HDMI adapters are all inexpensive and widely available. Make sure you buy an adapter that matches your specific ports — for example, HDMI female to DisplayPort male if your monitor has HDMI and your computer has DisplayPort.