Two numbers, two different jobs
People often use “refresh rate” and “frame rate” as if they were the same thing. They are related, but they describe different parts of the system.
- Frame rate is how many new images the game produces each second. It is set by the computer’s hardware and by how demanding the game is. It is measured in frames per second, or FPS.
- Refresh rate is how many times each second the display redraws its picture. It is a property of the monitor or television. It is measured in hertz, or Hz.
A game produces frames, and a display shows them. The refresh rate is the most that the screen can update, and the frame rate is how much the game is giving it to update with.
What the display does
A display does not show a frame the instant it is made. It redraws its whole picture on a fixed schedule. A monitor with a refresh rate of 60 Hz redraws 60 times every second, so it begins a new refresh roughly every sixteen and a half thousandths of a second (one second divided by 60). A 120 Hz display begins a new refresh about twice as often, roughly every eight and a third thousandths of a second.
At each refresh, the display shows whatever the computer has most recently handed over. If the computer has a new frame ready, the screen shows it. If not, the screen shows the previous frame again.
What the game does
The game, meanwhile, does not run on the display’s schedule. Each frame takes however long it takes: the processor works out the game state, the graphics card draws the scene, and then the frame is ready. A simple scene may be drawn quickly, while a busy one takes longer. That is why the frame rate rises and falls during play. The wider topic of frame rate and performance is covered elsewhere, so here we focus on how it meets the display.
What happens when they do not match
Because the two run on separate clocks, they can drift in and out of step. Several things can follow.
Frame rate lower than the refresh rate
If a game makes fewer frames than the display refreshes, some refreshes have no new frame to show, so the same frame is shown more than once. On a 60 Hz screen, a game running at 30 frames per second gives each frame two refreshes. That pattern is even, so it looks steady, although less smooth. If the frame rate is not a neat fraction of the refresh rate, some frames stay on screen longer than others, which can look like judder or uneven motion.
Frame rate higher than the refresh rate
If the game makes more frames than the screen can show, the extra frames are not displayed in full. A 60 Hz screen cannot show more than 60 distinct updates each second. Extra frames can still help in some games, because the game may respond to input with less delay when it runs faster, but you cannot see more than the display can draw. Sometimes the new frame arrives while the screen is partway through a refresh, and the screen shows part of the old frame and part of the new one. This visible split is screen tearing.
Ways of managing the mismatch
Several technologies exist to deal with the timing gap.
V-sync. Vertical synchronisation tells the graphics card to hand over new frames only at the moments the display is ready for them. It removes tearing, though it can add a small delay and, when the game falls below the refresh rate, can cause uneven pacing. The details are covered in the article on screen tearing.
Variable refresh rate. Technologies sold under names such as G-Sync and FreeSync let a compatible display change its refresh timing to follow the game’s output, within a supported range. Instead of the game waiting for the display, the display waits for the game. This usually reduces tearing and stutter without needing the delay that comes with v-sync, although results depend on the monitor and the settings.
Frame rate limits. Many games let you cap the frame rate. Capping it at or slightly below the refresh rate can produce steadier pacing and may reduce heat and noise, because the graphics card does less unnecessary work.
Does a higher refresh rate help?
A higher refresh rate means the screen can update more often, which can make motion appear smoother and can reduce how long each frame stays on screen. Many players, especially in fast competitive games, find this noticeable. How noticeable it is varies from person to person and from game to game, and the evidence of benefit in competitive performance is individual, so it is not reasonable to promise any particular improvement.
A high-refresh display only pays off if the computer can supply enough frames. A 144 Hz monitor running a game at 50 frames per second still shows about 50 distinct updates a second. In that case, the limits sit in the processor and the graphics card, the kind of bottleneck covered in the discussion of hardware bottlenecks.
It also helps to remember that there are other delays between pressing a button and seeing the result, such as the controller, the game’s processing and the display’s own response time. Together these make up input latency, which refresh rate affects but does not decide alone.
Reading specifications carefully
- A refresh rate rating is a ceiling for what the screen can show, not what you will see in every game.
- Response time and refresh rate are different measurements. The first is about how quickly pixels change colour, the second about how often the picture updates.
- Connection type matters. Some cables and ports limit the highest refresh rate available at a given screen resolution, so check what your hardware supports.
- Check your operating system settings. A monitor can be left running at a lower refresh rate than it is capable of until you change it.
Summing up the relationship
The frame rate is what the game gives; the refresh rate is how often the screen can take it. Smooth play comes from the two working together, with frame output steady enough that each refresh has something good to show.