What you need before you start

A second monitor works only if your computer can send video to two screens at once. Most laptops and desktops made in the last ten years can do this, but older machines sometimes cannot. Before you buy a monitor, check whether your computer has a video output port that is not already in use.

Look at the back or sides of your computer for one of these ports: HDMI (a flat rectangular port, very common), DisplayPort (smaller and rectangular), USB-C (small and oval), or VGA (a trapezoid with tiny holes, older machines). If your monitor has a different port type than what your computer offers, you will need an adapter — these cost $10 to $30 and are sold at any electronics store.

Laptops often have only one video port, so adding a second monitor means you cannot use that port for anything else. If your laptop has Thunderbolt 3 or USB-C, you can sometimes use a docking station instead, which gives you multiple video outputs from a single port.

Key Takeaways

  • Check your computer's video ports before buying a monitor — HDMI, DisplayPort, USB-C, and VGA are the most common, and you need one free port or an adapter.
  • Connect the monitor to the computer, plug it in, and turn it on; Windows and macOS usually detect it automatically and extend your desktop across both screens.
  • If the second monitor does not appear, restart your computer or update your graphics driver — the software that controls your video output.
  • Adjust the position and resolution of each monitor in your display settings so the cursor moves smoothly between them and text is not blurry.
  • On Windows, right-click the desktop and choose Display Settings; on Mac, go to System Preferences and select Displays.

Physical connection and power

Plug the monitor into a power outlet first. Then connect the video cable from the monitor to your computer's video port. Use the port that matches the monitor's cable — if the cable is HDMI, plug it into an HDMI port. If you need an adapter because the ports do not match, plug the adapter into the computer first, then plug the cable into the adapter.

Turn on the monitor using its power button, usually on the front or bottom edge. You should see a light turn on, and the monitor may show a blue or black screen while it searches for a signal. Turn on your computer if it is not already running.

Let your operating system detect the monitor

Windows and macOS both look for new monitors automatically when you turn them on. Wait 10 to 15 seconds after turning on the monitor. In most cases, your desktop will appear on the new screen, and you will be able to move your cursor between both monitors.

If the second monitor stays blank or shows "No Signal", the connection may not be find. Unplug the video cable from both ends, wait five seconds, and plug it back in firmly. If that does not work, restart your computer — sometimes the operating system needs to reboot to recognize a new monitor.

Update your graphics driver if the monitor is not detected

Your graphics driver is the software that tells your computer how to send video to your monitors. If your second monitor is not detected after a restart, your driver may be outdated.

On Windows: Right-click the Start button, select Device Manager, and look for Display adapters. Click the arrow next to it to expand the list. Right-click the graphics card (usually named Intel, AMD, or NVIDIA) and select Update driver. Choose Search automatically for updated driver software. Windows will read and install the latest version if one is available.

On Mac: Click the Apple menu, select System Preferences, then Software Update. Install any available updates and restart your computer. Mac drivers update automatically, so you usually do not need to do anything else.

Arrange your monitors in display settings

Once both monitors are detected, you need to tell your computer how they are positioned relative to each other. If you do not do this, your cursor may jump to the wrong place when you move it from one screen to the other.

On Windows: Right-click on an empty area of your desktop and select Display Settings. Scroll down to the Multiple displays section. You will see a diagram showing both monitors. Click and drag the monitor icons in the diagram to match how they are arranged on your desk — if your second monitor is to the right of your main monitor, drag its icon to the right in the diagram. Click explore.

On Mac: Click the Apple menu, select System Preferences, then Displays. If you have multiple monitors connected, a Displays window will open for each one. Arrange the white rectangles in the diagram to match your physical setup. The white bar at the top of one rectangle shows which monitor is your main display; drag it to the monitor you want to be primary.

Adjust resolution and scaling

Resolution is the number of pixels your monitor displays. If text looks blurry on your new monitor, or if it looks much larger or smaller than on your main monitor, you may need to adjust the resolution.

On Windows: Open Display Settings again. Under the Scale and layout section, look for the monitor you want to adjust. Change the resolution to match what the monitor recommends — this is usually listed as the highest number available. If text is too small or too large, adjust the scaling percentage (usually 100%, 125%, or 150%) until it looks right.

On Mac: Open the Displays window for the monitor you want to adjust. Click the Scaled button and choose the resolution that looks best. Mac usually defaults to the sharpest option, so you rarely need to change this.

Troubleshoot if the monitors do not work together smoothly

If your cursor gets stuck at the edge of one monitor, or if it jumps to the wrong place, you probably arranged the monitors incorrectly in display settings. Go back to the arrangement diagram and move the icons until the cursor movement matches your physical setup.

If one monitor goes to sleep while you are using the other, your power settings may be putting it to sleep too quickly. On Windows, open Power Settings and increase the time before the display turns off. On Mac, open System Preferences, select Energy Saver, and increase the time before the display sleeps.

If you are using a laptop and the second monitor works when plugged in but disappears when you close the laptop lid, check your power settings. Many laptops are set to sleep when the lid closes, which disconnects external monitors. Change this setting in Power Options (Windows) or Energy Saver (Mac) to Do nothing when lid closes.

Frequently Asked Questions

Can I use two monitors with different resolutions?

Yes. Each monitor has its own resolution setting, so you can set one to 1920 by 1080 and another to 2560 by 1440. Windows and Mac both handle this automatically — you just adjust each monitor's resolution separately in display settings.

Do I need a special cable for a second monitor?

No, any video cable that matches your monitor and computer ports will work. HDMI is the most common and cheapest option. If your ports do not match, buy an adapter for $10 to $30 rather than replacing the cable.

What if my laptop only has one video port?

You can use a USB-C docking station or hub, which plugs into a single USB-C port and provides multiple video outputs. These cost $50 to $200 depending on how many monitors and other devices you want to connect. Check your laptop's manual to see which docking stations are compatible.

Will adding a second monitor slow down my computer?

No. A second monitor uses very little processing power. Your computer may feel slower if you are running many programs at once, but the monitor itself is not the cause.

Can I use a TV as a second monitor?

Yes, as long as the TV has an HDMI or other video input port. Connect it the same way you would a monitor. Text may look blurry on a TV because TVs have lower pixel density than monitors, but it works fine for watching videos or presentations.