Free Online CPU Stress Tester
Put every core under steady load and see how your processor holds up.
This browser-based CPU stress test runs heavy calculations on all available threads at once. You watch how your computer responds: does it stay smooth, slow down, get loud, or crash? There is nothing to download, and closing the tab ends the test instantly.
Free Browser-Based No Installation
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Choose duration and stress level, then start a stress run — or run the full / single-core benchmark suite.
| CPU tier | Example devices | Typical score | Tier |
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How to use the CPU stress test
Four steps. The whole thing takes a few minutes.
- Open the test and prepare your system. Close extra browser tabs, chat apps and video calls. Background programs compete for processor time, and you want the test to measure your CPU, not your open apps.
- Start the CPU workload. Press Start and leave this tab visible. Browsers often slow down hidden tabs, which lowers the real load.
- Monitor your system. Open Task Manager on Windows (Ctrl + Shift + Esc) or Activity Monitor on macOS. Watch CPU usage, clock speed and how responsive the machine feels.
- Stop the test and review the results. Press Stop or close the tab. Then check what you saw against the guide below.
Run it for at least five minutes. Fifteen to thirty minutes gives a better look at sustained behavior, because many problems only appear once the heatsink and case are fully warm.
What does a CPU stress test do?
A CPU stress test keeps your processor working hard for a long stretch. It loads every core and thread with constant calculations, the kind of sustained work you get from a 4K video export, a big code compile or a long gaming session.
Normal use rarely does that. Most of the day your CPU idles or works in short bursts. A stress test removes the breaks. It holds the load steady so you can see whether your system stays stable, stays cool enough and keeps its speed.
The goal is not to break anything. The goal is to show you how your processor, cooler and power delivery behave when nothing lets up.
Why should you stress test your CPU?
Because problems hide at idle. They show up when the chip runs flat out and the cooling system has to keep pace. A stress test lets you find those weak spots on your schedule, not in the middle of a deadline.
- Check CPU stability. If a machine survives a long, steady load, you can trust it with real work. If it doesn’t, you know before it costs you a file.
- Test a newly built PC. A fresh build can hide a poorly seated cooler, a bad paste job or an unstable memory setting. A stress test exposes all three before you install your software.
- Check behavior under heavy workloads. Rendering, streaming, compiling and gaming all push a CPU for long periods. This test shows how your system copes with that kind of pressure.
- Troubleshoot crashes, freezes and unexpected restarts. If your computer fails under heavy tasks, a stress test lets you reproduce the problem on demand. That makes it far easier to trace.
- Evaluate cooling performance. After you clean a fan, replace thermal paste or install a new CPU cooler, run the test again. If throttling shrinks, the fix worked.
It also helps when you buy a used laptop or desktop. Run it before you hand over the money.
What to monitor during a CPU stress test
You will not get a single score from a stress test. Your computer’s behavior is the result. Five signals tell you most of what you need.
- CPU temperature. Heat is the main limit on sustained performance. Websites cannot read hardware sensors, so no browser-based tool can show you this number. Run a monitor such as HWiNFO, Core Temp or HWMonitor next to the test. Many Intel Core and AMD Ryzen processors can approach 95 to 100°C or more before they protect themselves, and your CPU’s spec page lists its exact limit (often called TjMax). A CPU that sits just under that limit for long stretches needs better cooling.
- CPU utilization. Task Manager or Activity Monitor should show usage climbing close to 100% across your cores. If it stays low, close other apps and make sure this tab is in the foreground.
- Clock speeds. Your CPU often starts fast, then settles lower as heat builds. A small dip is normal. A large, steady drop is a sign of thermal throttling.
- System stability. A freeze, an app crash, a blue screen or a sudden restart is the most important result a stress test can give you. Take it seriously.
- Thermal throttling. This is your CPU lowering its own speed and voltage to avoid overheating. It protects the chip, but it costs you performance. Common causes include dust in the heatsink, blocked vents, dried thermal paste and a failing fan.
| What you notice | What it usually means | What to do |
|---|---|---|
| Other apps feel slightly slower | Normal. All cores are busy. | Nothing |
| Fans spin up and get louder | Normal. Cooling is reacting. | Nothing |
| Clock speed drops after a few minutes | Thermal throttling or a power limit | Clean vents, improve airflow, retest |
| Cursor stutters, windows lag badly | System overloaded, or a cooling problem | Close apps and retest, then try a native tool |
| Freeze, crash or restart | Instability, overheating or a power issue | Check cooling first |
If your computer shuts down during the test, its thermal protection has probably done its job. A shutdown that comes within seconds, or at a load your hardware should handle easily, usually points to dust, poor airflow or worn thermal paste.
CPU stress test vs. CPU benchmark
The two get mixed up, but they answer different questions.
A stress test checks stability under sustained load. It asks whether your system stays responsive, cool and crash-free while working hard for a long time.
A benchmark measures speed. It asks how fast your CPU finishes a fixed task, then gives you a score you can compare with other processors.
| CPU stress test | CPU benchmark | |
|---|---|---|
| Question | Can my system stay stable under constant load? | How fast is my CPU compared with others? |
| Duration | Minutes to hours | Usually short |
| Result | How your system behaves | A comparable score |
| Examples | This page, Prime95, OCCT | Cinebench, Geekbench, PassMark |
Terms like CPU load test, CPU burn test and CPU torture test all describe the stress side. If you want to rank a Core i7 against a Ryzen 7, run a benchmark. If you want to know whether your machine survives a long workload, run this test.
Supported Platforms & Browsers
Browser compatibility and requirements
This test runs inside your browser, so it works with a modern, up-to-date browser such as Chrome, Edge, Firefox or Safari. You need a computer with a multi-core processor. Phones and tablets can run it, but they throttle quickly and give less useful results, so a laptop or desktop is the better choice.
A few limits shape the result:
- Background tabs. Many browsers slow down tabs you can’t see. Keep this one open and in front, or the load will drop.
- Browser overhead. JavaScript pauses for memory cleanup, and the page itself uses some CPU. That makes the test a little gentler than a native tool like Prime95 or OCCT.
- System and browser differences. Your result depends on your CPU, cooling, power settings, operating system and browser. The same machine can score differently in two browsers, so compare runs under the same conditions.
- Laptops. A laptop has less room for cooling than a desktop, so it throttles sooner and more often. Many laptops also limit CPU power on battery. For an honest cooling check, plug in the charger. To see what battery mode costs you, test both ways.
Treat this as a fast first check. If it finds a problem, you have your answer. If it finds nothing and you still suspect trouble, move to a native stress tool for a deeper pass.
Frequently asked questions
Is this CPU stress test free?
Yes. It costs nothing, needs no account and needs no installation.
Can I stress test my CPU online?
Yes. Open this page, press Start and let the test run in your browser. It loads your available CPU cores, and closing the tab stops it immediately.
How long should I run a CPU stress test?
Five minutes catches obvious problems. Fifteen to thirty minutes shows how your cooling behaves once everything is hot. Longer runs make sense after a new build or a hardware change.
Is it safe to stress test my processor?
On nearly every modern computer, yes. Intel, AMD and Apple chips include thermal protection built for heavy sustained load. The test creates real heat, like a long video render, so keep your vents clear and your laptop on a hard, flat surface. Stop the test if the fan sounds wrong or the machine gets uncomfortably hot.
How do I know if my CPU is stable?
Your system stays responsive, nothing freezes or crashes, and clock speeds hold fairly steady for the whole run. A small speed dip is normal. Crashes, blue screens, restarts or a sharp, lasting drop in speed point to a problem.
Can a CPU stress test damage my processor?
It is very unlikely. Your CPU slows itself or shuts the system down before heat can harm it. A browser test is no more dangerous than any other heavy workload. If your hardware is already faulty or badly overheating, a stress test can reveal that, but the test does not cause it.
Does this tool work on laptops?
Yes. Laptops throttle sooner than desktops because they have less cooling space, so a speed drop is normal. Test with the charger connected for the most accurate view.
Can this test show my CPU temperature?
No. Browsers can’t read hardware temperature sensors. Use HWiNFO or Core Temp alongside the test.
Why did my computer shut down during the test?
Most often, thermal protection stepped in. If it happened quickly, check your fans and vents for dust and blocked airflow.