--- title: "How much data does an idle Mac use? We measured it" url: "https://kilobat.app/idle-mac-data" description: "An idle Mac’s own background services used a median 1.5 MB an hour. iCloud sync added bursts of up to 101 MB. Measured by process with Kilobat." --- Measured · 32 idle hours · 31 October 2026 to 7 November 2026 # How much data does an idle Mac use? 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. [Download for Mac ↓](https://kilobat.app/downloads/Kilobat-1.35.1.dmg?via=site) ``` brew install seifip/kilobat/kilobat ``` 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. 1. [`cloudd`](https://kilobat.app/processes/cloudd)iCloud 11 MB 2. [`nsurlsessiond`](https://kilobat.app/processes/nsurlsessiond) 2.3 MB 3. [`syspolicyd`](https://kilobat.app/processes/syspolicyd) 672 KB 4. [`mDNSResponder`](https://kilobat.app/processes/mdnsresponder) 583 KB 5. [`networkserviceproxy`](https://kilobat.app/processes/networkserviceproxy) 195 KB 6. [`apsd`](https://kilobat.app/processes/apsd) 71 KB 7. `itunescloudd`iCloud 48 KB 8. [`trustd`](https://kilobat.app/processes/trustd) 38 KB 9. [`mobileassetd`](https://kilobat.app/processes/mobileassetd) 35 KB 10. `AMPLibraryAgent`iCloud 30 KB 11. [`softwareupdated`](https://kilobat.app/processes/softwareupdated) 21 KB 12. [`appstoreagent`](https://kilobat.app/processes/appstoreagent) 17 KB 13. `CategoriesService` 11 KB 14. [`assistantd`](https://kilobat.app/processes/assistantd) 10 KB 15. `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 MB**macOS background services, a quiet day **97 MB**macOS background services, an average day **352 MB**with 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 GB**macOS full installermacOS 27.2. Software Update usually sends a smaller package; Apple doesn’t publish its size. **9.9 GB**iPhone update, fulliOS 27.2 for iPhone 17 Pro. An iPhone 14 Pro’s is 8.7 GB. **3.4 GB**iPhone point updateiOS 27.0 to 27.2 on iPhone 17 Pro, from Apple’s update service. **up to 14 GB**Apple Intelligence modelsOf storage on newer Macs and iPhones, up to 8 GB on others. New models download with software updates. **3.1 GB**XcodeThe App Store download. Simulators and platform SDKs come separately. **256 MB**Safari updateSafari 27.2 for macOS Tahoe. **534 MB**Command Line ToolsThe developer tools many installers ask for. **23 MB**XProtect 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](https://kilobat.app/data/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](mailto: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](https://kilobat.app/processes/nsurlsessiond). **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 - [Apple software update catalog (installer, Safari, XProtect and Command Line Tools packages)](https://swscan.apple.com/content/catalogs/others/index-27-26-15-14-13-12-10.16-10.15-10.14-10.13-10.12-10.11-10.10-10.9-mountainlion-lion-snowleopard-leopard.merged-1.sucatalog.gz) - [Apple: iOS software update assets](https://mesu.apple.com/assets/com_apple_MobileAsset_SoftwareUpdate/com_apple_MobileAsset_SoftwareUpdate.xml) - [Apple: current software versions](https://gdmf.apple.com/v2/pmv) - [Apple: software update asset service (iPhone 17 Pro, queried 7 November 2026)](https://gdmf.apple.com/v2/assets) - [Apple Support: Get started with Apple Intelligence](https://support.apple.com/en-us/121115) - [Mac App Store: Xcode](https://apps.apple.com/us/app/xcode/id497799835?mt=12) - [Apple Support: Use Low Data Mode on your iPhone and iPad](https://support.apple.com/en-us/102433) - [Apple Support: If your iCloud Photos aren’t syncing](https://support.apple.com/en-us/101559) Checked on 7 November 2026. ## See what your Mac sends when you're not looking. [Download for Mac ↓](https://kilobat.app/downloads/Kilobat-1.35.1.dmg?via=site) ``` brew install seifip/kilobat/kilobat ```