Open Activity Monitor on a Mac running Slack and you'll find it sitting quietly at the top of the memory list, sometimes ahead of Chrome, often ahead of everything else. Two gigabytes is a common figure. After a long week of continuous use, three is not unusual. For a messaging app, those numbers feel hard to justify.
They make more sense once you understand what Slack actually is under the hood. It's not a lightweight native app built by Apple engineers for macOS. It's a web application running inside a bundled browser. And that distinction explains almost everything.
Why does Slack use so much memory?
Slack is built on a framework called Electron. Electron lets developers build desktop apps using web technologies like HTML, CSS, and JavaScript, which is the same stack used to build websites. The trade-off is that every Electron app ships with a complete copy of Chromium - Google's open-source browser engine - bundled inside it. When you launch Slack, you are, in effect, launching a browser.
RAM (the temporary workspace your Mac uses to hold whatever's currently running) gets allocated heavily from the start because Slack needs to spin up that browser engine before it can do anything else. This baseline cost exists even before a single message has loaded.
It doesn't stop there. Each Slack workspace you're signed into runs as its own renderer process, roughly equivalent to an additional browser tab. If you're in three workspaces, Slack is running three separate processes, each holding its own copy of that workspace's data, interface, and state in memory. Two workspaces is common for people who work with external partners or use a community workspace alongside their company one. Three or four isn't unusual for freelancers or contractors.
What is Electron, and why does it matter?
Electron lets developers build desktop apps using web technologies, so a company can take its existing web app and wrap it inside a Chromium shell rather than rewriting everything for each platform. The result looks like a native desktop app but runs web code underneath. One codebase works on Mac, Windows, and Linux, which is why Slack, VS Code, Discord, and many other widely-used tools chose it.
The downside for users is memory. A native macOS app shares system frameworks with the operating system and other apps, keeping its footprint small. An Electron app brings its own full browser engine, which adds hundreds of megabytes before the app's own code has run. Slack Engineering has documented efforts to reduce the app's memory footprint, and it is more efficient than earlier versions, but the Electron architecture sets a floor that native apps don't have.
How much Slack memory is normal?
Here's a realistic breakdown of what to expect:
- One workspace, freshly launched: typically 400-700 MB. Slack needs its Chromium core plus the workspace's interface and initial data.
- Two or three workspaces: 1-2 GB is normal. Each additional workspace adds its own renderer process and memory allocation.
- After a full day of use: memory tends to grow. The same session that started at 1 GB may be sitting at 1.5 GB or 2 GB by late afternoon as Slack caches more data and its processes accumulate state.
- After several days without restarting: 3 GB or more is possible. Slack's memory usage grows over extended sessions. Quitting and relaunching resets it.
None of these figures mean Slack is broken. They're the predictable result of the architecture. Whether they cause a problem depends on your Mac's total RAM and what else is running alongside Slack.
The best place to check is Activity Monitor (press Command-Space, type "Activity Monitor", press Return). Click the Memory tab. Look at the Memory Pressure graph at the bottom. If it's green, Slack is heavy but your Mac is managing. If it's regularly yellow or red, the total memory demand from all your apps is pushing the limits of your system. For a full explanation of what that graph means, see what memory pressure means on Mac.
How to reduce Slack memory use
A few things genuinely help:
Quit Slack at the end of the day. Not close the window - actually quit. Press Command-Q or right-click Slack in the Dock and choose Quit. This is the single most effective thing you can do. Quitting clears Slack's accumulated memory entirely. Relaunching it fresh the next morning resets usage back to its starting point. If you've never done this and Slack has been running for days or weeks, you may be surprised by how much memory this frees up.
Sign out of workspaces you don't need active. Each open workspace is its own renderer process. If you're signed into a community workspace you haven't checked in a week, or a former employer's workspace, signing out reduces Slack's memory proportionally. You can always sign back in when you need it.
Disable rich link previews and animations. In Slack preferences, under Accessibility, you can turn off animated images and GIF autoplay. Under Messages and Media, you can disable inline media previews. These don't save enormous amounts of memory, but they reduce the amount of content Slack keeps loaded and can make a modest difference over a long session.
Consider using Slack in a browser tab. Opening app.slack.com in Safari or Chrome instead of using the desktop app typically uses roughly half the memory, because the browser tab shares your existing browser's infrastructure rather than running a separate Chromium instance. The trade-offs are real: you lose native notifications that work when the browser is in the background, global keyboard shortcuts like the one that jumps straight to Slack from any app, and the separate Dock icon. If you're on an 8 GB Mac and memory is consistently tight, it's worth trying for a day and seeing whether you miss what you lose.
For general guidance on freeing up RAM across your whole Mac, not just from Slack, the companion post how to free up RAM on Mac covers all the main approaches.
Should I use Slack in a browser instead?
It depends on how central Slack is to your day. If Slack is something you glance at occasionally, the web version is an easy win: half the memory, nothing to install, and you lose very little. Going to app.slack.com in Safari and bookmarking it takes thirty seconds.
If Slack is where much of your work happens, the native app is harder to replace. The global shortcut that switches you to Slack from anywhere, background notifications that arrive whether the browser is in focus or not, and the Dock badge for unread messages all matter more the more heavily you use the app.
There's a middle ground worth considering. If you run Chrome alongside Slack, your Mac is running two Chromium instances simultaneously. Switching to Slack in a Chrome tab eliminates one of those entirely. The impact is larger than you'd expect. For more on Chrome's memory behaviour, see Chrome on Mac: why it eats RAM.
When is Slack's memory use actually a problem?
The same principle applies here as with any heavy app: it's only a problem if your Mac shows signs of struggling.
Slack using 2 GB on a 16 GB Mac is not a problem. There's enough headroom and you won't feel it. Slack using 2 GB on an 8 GB Mac, while Chrome, Mail, and a couple of other apps are also running, is a different situation. Your Mac starts running short of workspace and compensates by using the SSD as temporary memory - a process called memory swapping. The SSD is much slower than RAM, and this is when you'll notice apps taking longer to respond, the feeling that switching between things is slightly sticky, or the fan running more than usual.
Signs Slack's memory use is actually causing trouble:
- The Memory Pressure graph in Activity Monitor is regularly yellow or red.
- Other apps slow down noticeably when Slack is open.
- Slack itself becomes sluggish toward the end of a long session, with messages taking a moment to render or search feeling slow.
- Quitting Slack makes everything else feel faster almost immediately.
If none of those apply, Slack's memory use is high but not harmful. If they do, quitting Slack daily and reducing open workspaces are the highest-impact steps. And if the problem persists across multiple apps, the underlying issue may simply be that 8 GB of RAM is a tight budget for modern work software. That's not Slack being broken; it's worth knowing about. For a broader look at diagnosing a slow Mac, see how to free up RAM on Mac.