Glossary
Energy impact
A relative measure of how much energy an app is using right now. Lower is better.
What it is
Energy Impact in Activity Monitor is a relative, unitless score of how much energy an app is using right now, where lower is better. It combines CPU time with how often the app wakes the processor, GPU use, and disk and network activity. Use it to compare apps on your Mac, not as a wattage.
It's in the Energy tab, next to 12 hr Power on a MacBook. If the battery drains while the lid is closed, Energy Impact won't show it: look at sleep assertions and dark wakes instead.
Why it matters
On a laptop, energy impact tells you which app is costing you battery. An app with modest CPU can still have high energy impact if it wakes the Mac constantly.
In Activity Monitor
The Energy tab: Energy Impact now, and 12 hr Power, the average over the last 12 hours or since the Mac started.
In iKnowMyMac
The Battery tab lists apps sorted by energy, the Overview shows power by app, and Sleep & Battery shows overnight drain by app.
top -l 2 -o power -n 10 -stats pid,command,cpu,powerThe ten processes with the highest power figure. Like Energy Impact, it's a relative score.
A relative score, not a measurement
Apple describes Energy Impact as a relative measure of an app's current energy consumption, where lower is better. It's built from several different measurements, such as CPU, storage and network use, and an Apple engineer explains that this is why it's documented as an abstract value rather than a unit. So it isn't a wattage, it doesn't convert into battery percentage or hours of battery life, and no figure is “too high” on its own.
- Compare apps with each other, not with numbers you read online. A score means something next to the other apps in the list, on your Mac.
- Don't compare with other Macs. The score is built from different measurements on different hardware, so a figure from someone else's Mac tells you little about yours.
- Look at duration. A spike while a page loads is normal. An app that stays near the top for minutes is the one worth a look.
Energy Impact now versus 12 hr Power
The Energy tab shows two different views of the same idea. On a MacBook it also has a 12 hr Power column; Apple describes it as the app's average energy impact over the last 12 hours, or since the Mac started.
| Energy Impact now | 12 hr Power | What it usually means |
|---|---|---|
| High | Low | A burst happening right now: a page loading, an export, an update. Wait a minute and look again. |
| Low | High | The app was busy earlier, possibly while you weren't looking or while the Mac was meant to be asleep. |
| High | High | Sustained use. This is the app to investigate. |
| Low | Low | Not your battery problem, whatever else it is doing. |
High
- 12 hr Power
- Low
- What it usually means
- A burst happening right now: a page loading, an export, an update. Wait a minute and look again.
Low
- 12 hr Power
- High
- What it usually means
- The app was busy earlier, possibly while you weren't looking or while the Mac was meant to be asleep.
High
- 12 hr Power
- High
- What it usually means
- Sustained use. This is the app to investigate.
Low
- 12 hr Power
- Low
- What it usually means
- Not your battery problem, whatever else it is doing.
The Energy tab has two more columns worth reading: App Nap, which shows whether macOS has put an app's background work on hold, and Preventing Sleep, which shows whether the app is keeping the Mac awake.
How to investigate an app that stays high
- Confirm it's sustained. Sort the Energy tab by Energy Impact and watch for a few minutes. If the app falls back, there's nothing to fix.
- Check the CPU tab. Sort by % CPU, and add the Idle Wake Ups column (View → Columns) if it isn't shown. An app with modest CPU but thousands of wake-ups keeps the processor from resting, which costs energy too.
- Check the GPU. Choose Window → GPU History. Video, animation, games and machine learning show up here rather than in % CPU.
- Check disk and network. Sort the Disk and Network tabs by the same app. Sync clients, backups and downloads score high because of input and output, not computation.
- For a browser, find the tab. The browser's own task manager names the tab or extension. See Google Chrome Helper using too much memory or CPU.
- Then act on the cause. Quit or restart the app, pause the sync or job, close the tab, or update the app. If an app you aren't using stays high every day, check for an update or contact its developer.
When the battery drains while the Mac is asleep
Energy Impact describes the Mac while it is awake. If you lose charge with the lid closed, the cause is usually a Mac that didn't stay asleep or kept waking, which the overnight battery drain guide shows how to find.
FAQ
Questions
Something else? support@iknowmymac.com
What is Energy Impact in Activity Monitor?
A relative score of how much energy an app is using right now, shown in Activity Monitor's Energy tab. Lower is better. It has no unit, so compare apps with each other on your Mac rather than reading it as watts.
What does a high Energy Impact number mean?
That the app is using more energy than the others in the list right now. A spike while a page loads is normal. An app that stays near the top for minutes, or also tops the 12 hr Power column, is the one costing you battery.
Why is Energy Impact high when % CPU is low?
Energy Impact also counts how often an app wakes the processor, GPU use, and disk and network activity. An app that wakes the Mac thousands of times a minute, or plays video, can score high with modest CPU.
Does Energy Impact show battery drain while the Mac is asleep?
No. It describes the Mac while it's awake. For drain with the lid closed, check what's keeping the Mac awake and the dark wakes in the power log; the overnight battery drain guide walks through both.
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