GPU stress test

GPU load levels

If you have a fast desktop graphics card, pick Max. On one we tried, Max pushed it close to full use while Heavy fell well short. Each level draws a 1024 by 1024 pixel scene 8 times a frame: Light does 256 shader steps per pixel, Medium 4 times as many, Heavy 16 times and Max 256 times. No level lets a frame take longer than 50 ms, so on a slow chip Light and Max can end up at the same load.

CPU mode

CPU mode keeps your processor busy with loops on separate threads. Heavy starts one thread per logical processor your browser reports, Medium half as many and Light a quarter. MDN describes these Web Workers as real operating system threads. Max starts twice as many as Heavy, because Safari and Firefox private windows always report 4 or 8 processors, whatever your machine has, as MDN's compatibility data and Firefox's source code show. So in Safari, on a phone or a Mac, pick Max.

Signs of a failing GPU

UL, the maker of 3DMark, says crashes, freezes or visual glitches during a stress test can mean a stability problem. Here, glitches show up as specks, streaks or wrong colors in the rings. A dot that stays put after the test stops is a fault in the screen itself, which the dead pixel test checks. On Windows, a flicker and a message that the display driver stopped responding mean Windows reset a graphics chip that was stuck on one task for more than 2 seconds, Microsoft's driver documentation says.

If your frame rate drops while the load stays the same, the card has slowed down. 3DMark scores this as stability: the slowest loop divided by the fastest, with 97% or more counting as a pass. We work out the same ratio over 20 parts of the run.

What a web page can't measure

• Sensors No web page can read your graphics chip's temperature, clock speed, usage or power. MDN's reference shows WebGPU only gives the maker, architecture, device and a description.
• Speed past the refresh rate Browsers update a page once per screen refresh, MDN notes, so a card with power to spare looks the same as one barely keeping up. You only see the load once frames take longer than a refresh.
• An overclock check This test stops adding load once frames reach 50 ms. FurMark and OCCT have no such limit, and OCBASE, OCCT's maker, says OCCT can hold a set load, sweep it or spike it, shows voltages and fan speeds, and tests every VRAM chip for faults. To check an overclock, use one of those.
• The chip in use On Windows, Chrome runs WebGPU on the same graphics chip as the rest of Chrome, which on a laptop is often the built-in one, and the readout shows which. To switch to the faster one, Google's WebGPU troubleshooting guide points to chrome://flags/#force-high-performance-gpu.

How the GPU stress test works

When you press Start, we skip one second, then measure 2 seconds with no load: the same frame rate the FPS test shows. If it shows 60 on a faster screen, the refresh rate test can find what's limiting it. Then the load grows every frame, by one step or a tenth, whichever is bigger, and the results count from the moment it reaches your level.

To keep your machine safe, we never queue more than 2 frames on the chip, and we halve the work if frames keep taking longer than 200 ms. The test stops if no frame finishes within a second or you switch tabs. If your browser resets its graphics, we wait for you to press Start again, because Chromium's source code shows Chrome blocks WebGL and WebGPU on a site that loses its graphics twice within 2 minutes.