Stress / 07

Thermal reveal.

Runs the CPU benchmark twice back-to-back. A drop greater than 15% between cold and hot scores means the chip is throttling under sustained load.

Notes

No temperature sensor — this is a behavioural proxy. To see absolute temps, use HWiNFO64 (Windows) or iStat Menus (macOS) alongside this test.

How it works

We run the same multi-threaded SHA-style hash workload twice in immediate succession — 6 seconds each, full thread count both times. The first ('cold') run sets the ceiling; the second ('hot') reveals how much performance the cooling system is conceding to heat.

The headline metric is the hot run; the metric tile labelled 'Performance held' is the ratio. Anything under 85% across two short back-to-back runs almost always means sustained temperatures above 90°C — which corresponds to OS-level CPU throttling.

Related
CPU benchmark
Single-run scaling test — establishes the cold ceiling.
Wizard: laptop overheating
Auto-flow that runs this and generates a verdict + checklist.
Frame-time stress
Detects thermal throttling indirectly via animation jitter.
Frequently asked

Why two CPU runs instead of measuring temperature?

Browsers cannot read CPU temperature directly — there's no Web API for thermal sensors (rightly, that would be a fingerprinting attack vector). Back-to-back benchmarks are the next-best proxy: a healthy laptop holds its score across consecutive runs; a throttling one drops measurably.

What's a normal hot/cold ratio?

Above 90% (≤10% drop) is healthy — cooling is keeping up. 80-90% is mild throttling, common on thin laptops under sustained load. Below 80% is significant — usually a dusty heat-sink, dried thermal paste, or blocked airflow. Below 70% is severe and worth servicing.

Does this work on a phone or tablet?

Yes, especially well. Phones throttle aggressively under sustained load — most phones hold under 70% by the end of a 30-second benchmark. This test surfaces it directly: if your phone scores 5000 ops cold and 3200 ops hot, you know it's CPU-thermal-limited rather than under-spec.

Why is my desktop showing throttling?

Three usual suspects: stock thermal paste has dried (4+ year-old build), case airflow is poor (front intake fans missing or blocked), or CPU cooler isn't large enough for the chip (small air cooler on a 65W+ chip). The CPU might also be running stock voltage when it could undervolt to drop temps 10°C.

Can I trust the number if other apps are running?

Background load adds noise. Close heavy tabs and apps before running, and don't move your mouse during the test. The second run still surfaces throttling even with some background noise — the relative drop matters more than absolute scores.

Related tools in Stress
CPU benchmark
Multi-thread hash workload.
WebGL benchmark
Triangle throughput, shader complexity.
WebGPU compute
Compute-shader throughput in GOps/s.
Hash benchmark
SHA-256 throughput in MB/s.
Memory pressure
Allocation ceiling probe.