Why CPU benchmarks differ across browser engines

You may run the same browser CPU benchmark on the same computer and get different scores in Chrome, Firefox, or Safari. That does not automatically mean your processor changed or that one browser is broken.

A browser test depends partly on the browser engine running it, as well as your computer's power and workload. Use the Processor Test to compare the single-core and all-core results, then follow the checks below to see whether the difference is meaningful.

Compare the CPU test in two browsers

1. Open the Processor Test in your first browser and run the test. Note the single-core and all-core scores.
2. Open Browser Info in that browser and note its engine and version. The engine is the part of the browser that runs website code.
3. Open the Processor Test in the second browser on the same computer. Run it under the same conditions and record both scores.
4. Repeat each test a few times. Compare the typical results, not just the highest score from one run.

Keep other conditions as similar as you can. Use the same computer, power connection, room conditions, and browser settings. A result from a laptop on battery is not a fair comparison with one taken while it is plugged in.

What the result means

One browser scores higher on both tests

The browser engines may handle the test's calculations differently. Engines such as Chromium's V8, Firefox's SpiderMonkey, and Safari's JavaScriptCore use different methods to compile and optimize website code. The operating system and browser version can also affect how that code runs. A higher score means the test completed faster in that particular setup, not that the processor itself has changed.

Single-core scores differ more than all-core scores

The single-core result depends heavily on how quickly one processor core can run the test, including how the browser schedules work and how quickly the core can boost its speed. Small differences in background activity or power settings may show up clearly here.

All-core scores change more from run to run

Using several cores at once creates more heat and uses more power. A laptop may lower its processor speed as it warms up, or change its speed to stay within its power limit. Close other demanding programs and let the computer cool before repeating a comparison.

Scores vary even in the same browser

That is common when a computer is busy, warming up, or switching between power states. Browser tabs, extensions, updates, and other apps can also compete for processor time. If repeated runs settle around a similar score, treat that as more useful than a single unusually high or low result.

The numbers look different, but both are out of 100

The Processor Test reports a score out of 100 for its own test. It is not a percentage of processor use and should not be treated as a universal score shared by every browser benchmark. Use it to compare runs of this test under controlled conditions, rather than to make a direct claim about all browser or desktop workloads.

How to make the comparison fair

1. Use the same power conditions. On a laptop, connect the charger for both tests. In Windows 11, open Settings › System › Power & battery (on some PCs, Settings › System › Power) and choose Best performance under Power mode. On a Mac, open System Settings › Battery and turn off Low Power Mode for the comparison. Keep the setting the same in both browsers.
2. Let the computer settle. Close games, video exports, and other processor-heavy tasks. Wait for downloads or software updates to finish, then give the computer a minute before starting the test. Avoid testing one browser immediately after a long, hot workload and the other while the computer is cool.
3. Keep the browser versions current. An engine can change how it compiles code between releases. Check each browser's version, and note it with the score. The Browser Info tool shows the browser engine and version, which helps you identify what you actually compared.
4. Reduce browser add-ons and background tabs. Extensions and open pages can use processor time or change how a page runs. Close extra tabs and, if the difference seems unusually large, temporarily disable extensions before repeating the test. Restore your usual settings afterward.
5. Compare repeated runs. Run the test more than once in each browser, alternating which browser you test first if possible. If one result is an outlier, repeat it. A consistent gap across several runs is more likely to reflect a real difference in that browser and setup.

Why the browser engine matters

A browser benchmark does not run directly on the processor in the same way as every installed desktop benchmark. The browser interprets or compiles the page's code, manages its work, and communicates with the operating system. Different engines can make different choices about those steps, so a test can take a different amount of time even when the computer is unchanged.

The gap may also shrink or grow after a browser update, an operating system update, or a change in power mode. That is why a score is most useful as a before-and-after check when you keep the browser and conditions consistent. It is less useful as a precise way to rank processors from results collected in different browsers.

If one browser repeatedly scores lower, but the difference does not appear in your everyday tasks, the benchmark gap alone is not a reason to replace hardware.