Measured · 32 idle hours · 31 October 2026 to 7 November 2026

How much data does an idle Mac use?

Name: Idle Mac data use by process
Creator: Kilobat
License: https://creativecommons.org/licenses/by/4.0/

We left a MacBook Air (M4), macOS 27.2 awake with the display off and let Kilobat count every byte, process by process. macOS’s own background services used a median 1.5 MB an hour. iCloud sync comes on top, and depends on what you keep in iCloud.

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One idle hour · MacBook Air (M4), macOS 27.2

macOS, median: 1.5 MB
macOS, average: 4.0 MB
iCloud sync, average: +11 MB
Apps left open: +99 MB

iCloud synced in 11 of 32 hours, up to 101 MB in one

By process

Which parts of macOS used it.

Average data per idle hour, sent and received, for each Apple process Kilobat saw. Sync processes move your own iCloud content, so they’re marked apart. Each one links to what it is and why it connects.

clouddiCloud 11 MB
nsurlsessiond 2.3 MB
syspolicyd 672 KB
mDNSResponder 583 KB
networkserviceproxy 195 KB
apsd 71 KB
itunesclouddiCloud 48 KB
trustd 38 KB
mobileassetd 35 KB
AMPLibraryAgentiCloud 30 KB
softwareupdated 21 KB
appstoreagent 17 KB
CategoriesService 11 KB
assistantd 10 KB
newsd 9 KB

cloudd is iCloud’s sync daemon. It does nothing for most hours, then moves tens of megabytes when something you keep in iCloud changes, here or on another device. How much depends entirely on what you store.

Per day

What a day of idling costs on a hotspot.

36 MBmacOS background services, a quiet day

97 MBmacOS background services, an average day

352 MBwith this Mac’s iCloud sync

On a 1 GB travel eSIM, a day of macOS’s background services is about 10% of the plan. iCloud sync and apps left open are what usually empty it, along with the occasional big download below.

The big ones

The occasional downloads that empty a plan.

Idle hours cost megabytes. These cost gigabytes, and they come when Apple ships an update. Sizes are Apple’s own, from its update catalogs and pages.

17.8 GBmacOS full installermacOS 27.2. Software Update usually sends a smaller package; Apple doesn’t publish its size.

9.9 GBiPhone update, fulliOS 27.2 for iPhone 17 Pro. An iPhone 14 Pro’s is 8.7 GB.

3.4 GBiPhone point updateiOS 27.0 to 27.2 on iPhone 17 Pro, from Apple’s update service.

up to 14 GBApple Intelligence modelsOf storage on newer Macs and iPhones, up to 8 GB on others. New models download with software updates.

3.1 GBXcodeThe App Store download. Simulators and platform SDKs come separately.

256 MBSafari updateSafari 27.2 for macOS Tahoe.

534 MBCommand Line ToolsThe developer tools many installers ask for.

23 MBXProtect updateApple’s malware definitions, updated in the background.

On an iPhone, Low Data Mode turns off automatic updates and pauses iCloud Photos and backups. On a Mac, mark the hotspot as Low Data Mode in its Wi-Fi details and hold updates until you’re on Wi-Fi you don’t pay for. Kilobat holds updaters back on metered networks and shows what’s using data, live.

Method

How it was measured.

Kilobat records how much each app and process sends and receives, in hourly buckets, on the Mac itself.
macOS’s power log (pmset -g log) records when the display turned off and on and when the Mac slept and woke.
An hour counts as idle when the Mac was awake with the display off for at least 50 minutes of it, and the display was on for no more than 10. Other hours are left out.
“macOS background services” is Apple’s own processes, minus the ones that sync your content (cloudd, iCloud Drive, Photos and the Music library), which are counted as “iCloud sync”. Every other app is one figure, “apps left open”, so nothing about what the owner runs is published.
Kilobat doesn’t run while the Mac sleeps, so Power Nap traffic isn’t in these numbers.
The figures are from one Mac. iCloud, Photos and app settings change them a lot, so treat them as an example, not a law.

The data is free to use with a link: idle-mac.json (CC BY 4.0).

Your Mac

Measure your own Mac.

Kilobat is free to download. It shows live which apps and system processes are using the network, and keeps the history by the hour.

Terminal

# Data by day, and the apps that used it
kilobat report --summary --days 7
# One app or process, by hour
kilobat bandwidth cloudd day

Got a week of idle numbers from a different Mac? Send them to ping@kilobat.app and they’ll join the table.

Questions

How much data does a Mac use when idle?

On the Mac we measured, left awake with its display off, macOS’s own background services used a median 1.5 MB an hour and 4.0 MB on average. iCloud sync comes on top and depends on what you store: here it ran in 11 of 32 hours, up to 101 MB in one. Apps left open added 99 MB an hour.

Which process uses the most data on an idle Mac?

Usually iCloud’s sync daemon, cloudd, when something changed in your iCloud Drive, Photos or other synced data. Of the background services, nsurlsessiond used the most, 2.3 MB an hour on average. What nsurlsessiond is and why it connects.

Does a Mac use data while asleep?

A little: Power Nap and maintenance wake-ups let macOS check mail, iCloud and updates in the dark. Kilobat doesn’t run while the Mac sleeps, so this page measures the awake-but-idle state only.

How do I stop an idle Mac using hotspot data?

Mark the hotspot as Low Data Mode in Wi-Fi settings, pause iCloud Photos and app updates while you're on it, and quit apps you aren't using. Kilobat shows which apps and system processes are using data, live and by the hour.

How big is a macOS update?

The full macOS 27.2 installer is 17.8 GB in Apple’s software update catalog. Software Update usually sends a smaller package, and Apple doesn’t publish its size. An iPhone point update from iOS 27.0 to 27.2 was 3.4 GB on an iPhone 17 Pro.

Can I measure my own Mac?

Yes. Kilobat is free to download and records data use by app and process. kilobat report --summary shows totals by day; Pro, $29 once, adds budgets and alerts.

Sources

Checked on 7 November 2026.

See what your Mac sends when you're not looking.

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$ brew install seifip/kilobat/kilobat