CPU Stress Test

This CPU stress test runs a heavy workload on every logical processor your browser reports, so you can check that a computer stays stable and keeps its speed under full load. Each thread repeats integer, floating point or mixed calculations and checks every result against an answer that is known in advance. A wrong answer means the processor made a mistake, which is the classic sign of an unstable overclock or an overheating chip. It works in Chrome, Edge, Firefox and Safari on Windows, Mac, Linux and ChromeOS laptops and desktops, with Intel, AMD and Apple processors.

How to run a CPU stress test

1. Close games and other heavy programs, and plug a laptop into its charger.
2. Open a temperature monitor such as HWiNFO or Core Temp on Windows and keep it visible next to the browser.
3. Leave Threads on All to load the whole processor, or pick 1 thread to test the fastest single core speed.
4. Choose a workload. Mixed rotates integer, floating point and memory work and suits most checks. Floating point heats most processors the most.
5. Pick a run time and press Start stress test. Five minutes is enough for a first check.
6. Watch the graph, the Speed change readout and your temperatures. Press Stop or Esc to end the test early.
7. Press Copy results to paste the numbers into a forum post or a support ticket. Finished runs are saved under Your recent runs, so you can compare them later.

What the results mean

The thread tiles show each worker's speed. Two threads that share one physical core through Hyper-Threading or SMT each run noticeably slower than a thread with a core to itself, and on Intel processors with efficiency cores some threads run slower again. Neither is a fault.

The test finds calculation errors

Any number above zero in Errors is a failed test. Work through the causes from the most common:

• An unstable overclock or undervolt. Reset the BIOS overclocking settings to default, or undo the undervolt in Intel XTU, ThrottleStop or Ryzen Master, then run the test again. If the errors stop, the settings were too aggressive.
• Overheating. If the errors appear only after a few minutes, check your temperatures. Clean the cooler and fans, and replace dried thermal paste on a computer that is more than three or four years old.
• Intel 13th or 14th Gen desktop instability. Many Core i7 and i9 chips of these generations became unstable from excess voltage. Intel's fix comes as a motherboard BIOS update, so install the latest BIOS from your board maker. If errors continue at default settings, contact Intel, which extended the warranty on affected processors.
• Memory errors. The Mixed workload also exercises memory. If only Mixed fails, test the RAM with the ram test and then MemTest86.

Speed drops after a minute or two

A falling Speed change with no errors means the processor is throttling: it lowers its clock speed to stay within a temperature or power limit.

• Laptop power limits. Most laptops run fast for the first 30 seconds to 2 minutes, then settle to a lower sustained power. A drop of 5 to 15% at that point is normal.
• Power mode. On Windows 11, open Settings, then System, then Power & battery, and set Power mode to Best performance. On a Mac, turn off Low Power Mode in System Settings under Battery.
• Running on battery. Laptops cut processor power on battery. Plug in the charger and test again.
• Dust and old thermal paste. A drop that keeps growing through the whole run points to heat. Blow out the vents and fans, and keep a laptop on a hard, flat surface.

If the processor reaches its temperature limit within a minute, follow our laptop overheating fix guide.

The computer freezes, restarts or shuts down

A sudden shutdown under load is a hardware protection step, not a software crash.

• Thermal shutdown. The processor or the motherboard power stages got too hot. Check that the cooler is seated and its fan spins.
• Power supply. A desktop that restarts the moment all cores load may have a power supply that cannot hold its voltage. This shows up most often with an older or low cost unit.
• Unstable settings. A freeze with no heat warning usually means an overclock or memory profile that is not stable. Return the BIOS settings to default.

Fans get loud and the laptop gets hot

Loud fans and a hot keyboard deck during a CPU stress test are normal. Under full load, desktop processors usually sit between 60 and 85 °C, and thin laptops often reach 90 to 100 °C and hold there. Intel processors start throttling at their limit, between 100 and 110 °C depending on the model, and recent AMD Ryzen desktop chips are designed to run up to 95 °C. Compare your readings with our cpu temperature check guide. A laptop that is hot but keeps a steady score and no errors is working as designed.

Can a browser stress test a CPU properly?

A CPU stress test in a browser is a quick, safe first check with nothing to install, and it is enough to catch throttling and most unstable settings. It has real limits:

• It cannot read temperatures, clock speeds, voltages or power draw.
• It cannot use the widest vector instructions (AVX2 and AVX-512), so it draws less power than Prime95 or y-cruncher and heats the chip a little less.
• The browser and the system decide which core runs each thread.

For a full test, use these free tools:

On Linux, the sensors command from lm-sensors shows temperatures while stress-ng loads the processor. To check the rest of the system, run the gpu stress test for the graphics card, and the laptop battery tester to see how fast a heavy load drains the battery.

CPU stress test questions