How to benchmark a PC in your browser

Can you benchmark a PC without installing anything?

Yes. The CPU benchmark runs a fixed workload in your browser, first on one thread and then on every logical core, and scores how much work the processor gets through per second. The GPU benchmark does the same for graphics with a WebGL load. Neither needs an install, an account or admin rights, so they work on a shop's display model or a seller's laptop.

Per run: 5 s on one thread, then 5 s on every logical core

~11 s

Single-thread and multi-thread, in units per second

2 scores

Per machine before you compare typical results

3 runs

The trade-off is that browser scores measure the browser too. They're good for comparing machines and spotting problems, but they won't match native benchmark apps, and you should only compare scores taken in the same browser.

How to run the CPU benchmark

1. Plug in the laptop and close heavy apps and other browser tabs.
2. Open the CPU benchmark and press Start benchmark.
3. Leave the page alone for about 11 seconds: five seconds on one thread, then five seconds on every logical core.
4. Read the Single-thread score, the Multi-thread score, the Scaling factor and the Logical cores count.
5. Press Run again two more times. Each run is added to the Runs this session table so you can compare them.
6. Use the best or typical result, not the first one.

The workload is a prime sieve plus integer hashing and floating-point maths, run in JavaScript inside Web Workers. Every result is checked, so a broken run is never scored.

Your numbers will differ. The pattern is what to look for: the first run is often lowest, and scaling sits well below the core count.

Single-core vs multi-core: why both matter

The single-thread score is how fast one core runs. It drives how responsive a computer feels: opening apps, browsing, spreadsheets and most games lean heavily on one or a few fast cores.

The multi-thread score is the total across all cores working at once. It matters for work that splits into parallel pieces, such as video export, compiling code, 3D rendering and compressing files.

The scaling factor is the multi-thread score divided by the single-thread score. It's almost always lower than the core count, and that's normal. Hyper-threads share a physical core, efficiency cores are slower than performance cores, caches are shared, and processors run at lower clock speeds when every core is busy. A laptop with 16 logical cores might scale by well under 16.

A machine with a high single-thread score and a modest multi-thread score feels quick for everyday use. A low single-thread score with many cores can feel slow day to day, even if it renders video well.

Here's what this browser reports about the machine you're on now. The logical cores number is how many workers the benchmark's multi-thread phase starts.

What affects the score

When a processor gets hot, it slows down to protect itself, so a score that falls on every run points to cooling, while one that's low every time points to a setting. The score measures how fast the browser's JavaScript engine runs the workload, so Chrome, Edge, Firefox and Safari give different numbers on the same machine.

How to compare two computers fairly

1. Use the same browser on both, ideally the same version.
2. Plug both in and set the same power mode.
3. Close everything else, and wait a minute after start-up for background tasks to settle.
4. Run the CPU benchmark three times on each and compare typical results, not a single run.
5. Note the Logical cores count, and check the processor name in system specs so you know what you're comparing.

Expect some spread between runs. Differences of a few percent are noise. A big gap between two machines with the same processor usually means one is throttling, set to a power-saving mode, or busy in the background.

CPU benchmark vs GPU benchmark

The CPU benchmark tests the processor: general computing, app speed and the work that runs on the main chip. The GPU benchmark tests the graphics chip, which draws games, video effects and anything 3D.

The GPU benchmark renders a WebGL particle vortex at several load presets and tracks frame rate, 1% lows and frame time. Start with a light preset and check the FPS matches your refresh rate, then step up until it drops. A big gap between average FPS and 1% lows means stutter. It also shows the graphics chip the browser reports, which is a quick way to see whether a laptop is using its dedicated graphics or the processor's built-in graphics.

Run both. A fast processor with weak graphics is fine for office work but poor for games, and the reverse is rare but happens on older desktops with a newer graphics card.

Benchmarking a used PC before you buy

On a second-hand laptop or desktop, benchmarks show whether the machine performs like its spec says and whether it's overheating.

• Open system specs and check the processor, graphics, memory and operating system match the listing.
• Run the CPU benchmark three times in a row. Scores that fall noticeably each run point to throttling, which often means a cooling problem.
• Run the GPU benchmark on a medium preset for a minute and watch whether the frame rate holds steady.
• Finish with the full diagnostic, which runs ten automated checks across the display, graphics, audio, battery, processor, memory, storage, network and input, and gives you a report to save.

To compare with a listing or another machine, use the same browser you'll use for the benchmark at home. Our checklist for checking a used laptop before buying covers the screen, keyboard, battery and ports too.

Next, check the rest of the system

Run the GPU benchmark if you haven't yet, then the full diagnostic for a one-minute health check of the whole machine. If games feel choppy on a high refresh monitor, our guide to a 144Hz monitor showing 60Hz checks the display side.