How to tell if your Mac is thermal throttling

The check: thermal pressure

sudo powermetrics --samplers thermal -i 1000 -n 1

**** Thermal pressure ****
Current pressure level: Nominal

Nominal means no thermal limits. Any other level means macOS is holding the chip back, more as the level rises:

Level	What’s happening
Nominal	Full performance available
Light	Mild limits, often unnoticeable
Moderate	Noticeable slowdown under load
Heavy	Strong limits; long jobs take clearly longer
Trapping, Sleeping	Emergency levels; rare outside real faults

To watch it during a long build, sample every 2 seconds until you press Control-C:

sudo powermetrics --samplers thermal,cpu_power -i 2000

cpu_power adds the clusters’ frequency and power, so you can see clocks drop as pressure rises.

What about pmset -g therm?

You’ll see this command in older guides:

pmset -g therm

On Intel Macs it printed a CPU_Speed_Limit percentage. On Apple Silicon it usually prints only:

Note: No thermal warning level has been recorded
Note: No performance warning level has been recorded
Note: No CPU power status has been recorded

That doesn’t mean your Mac never throttles. These notes record rare warning events, not the everyday limiting Apple Silicon does. Use powermetrics for the current state.

Apps can also read macOS’s thermal state directly. It has four values: nominal, fair, serious and critical. Serious and critical mean the system is actively cutting performance to cool down.

Signs you’re throttling

• A build or export starts fast, then slows down after a few minutes.
• kernel_task shows high CPU in Activity Monitor while the Mac is hot. macOS uses it to keep CPU time away from apps. See kernel_task.
• Games or 3D apps drop frames after a while, not at the start.
• Benchmarks score lower on the third run than the first.
• On a MacBook Pro or Mac mini, fans are at or near full speed.

Why it happens

Throttling is the chip staying within its limits. The usual reasons it kicks in:

1. Sustained full load. Compiling, rendering, running a local LLM or a test suite in a loop for many minutes.
2. No fan. Every Apple Silicon MacBook Air relies on its case to shed heat and reaches its limit sooner.
3. Blocked airflow. A MacBook on a bed, couch or in a sleeve-like stand can’t breathe through its vents.
4. Hot room or direct sun. The cooler can only work against the air around it.
5. Charging while working hard. Charging adds heat to the same chassis.
6. Background work. Spotlight, Photos or a forgotten watcher adding load on top of yours.

How to avoid it

• Find extra load. Sort Activity Monitor’s CPU tab and stop what you don’t need. A stray node or Docker container steals thermal headroom from your build.
• Raise the Mac. A stand improves airflow on a MacBook Pro and lets an Air’s bottom case shed heat.
• Start fans earlier. On a Mac with fans, a fan curve that ramps up sooner than Apple’s default can keep clocks up longer during long jobs, at the cost of noise.
• Split the work. For a fanless Air, long renders or compiles finish sooner on a Mac with active cooling. If you do this every day, that’s the real fix.
• Cool the room. Even a few degrees of ambient temperature helps fanless Macs.

Temperatures themselves are a weaker signal than pressure, but it helps to know what’s normal: see normal Apple Silicon temperatures.

Seeing it live

Stat Space’s System tab shows a thermal pill (Cool, Warm, Hot · throttling) from macOS’s thermal state, without sudo, next to temperatures, power in watts and fan speeds. When the Mac runs hot, a notice in the same tab says so, and temperature alerts can notify you when it stays hot. History keeps per-minute temperatures, power, fans and clocks for 30 days, so you can see when a long build started slowing down. All free; Pro’s spike rewind also records the top three processes each time temperature crosses your threshold.