How to Lock the Dock Size on Mac So It Can't Be Changed

The Dock has an invisible trap built in: the divider line near the Trash is a drag handle, and one stray swipe while aiming for an icon resizes your whole Dock. If you've ever looked down to find your icons mysteriously huge — or share the Mac with kids who find the handle irresistible — macOS has a hidden setting that freezes the Dock's size completely. Works on Ventura, Sonoma, and Sequoia.

Step 1: Set the size you actually want

Locking freezes the current size, so dial it in first. Either use the slider in System Settings → Desktop & Dock → Size, or set an exact, repeatable value from Terminal:

# set an exact icon size in points (roughly 16–128)
defaults write com.apple.dock tilesize -int 48
killall Dock

48 is a sensible medium; laptop minimalists tend to like 36–44, big-display users 56–64.

Step 2: Lock it

# freeze the Dock size
defaults write com.apple.dock size-immutable -bool true
killall Dock

Test it: hover over the Dock divider — the resize cursor still appears, but dragging does nothing. The Size slider in System Settings stops having any effect as well. Your Dock is now exactly as big as you decided, permanently.

Unlock when you change your mind

# make the Dock resizable again
defaults delete com.apple.dock size-immutable
killall Dock

The slider and the divider drag come straight back. Nothing about your Dock's contents or current size changes on unlock — only the ability to change it.

Why bother locking a size?

• Accidental drags are common. The divider sits right next to the Downloads stack and the Trash — the two most-clicked targets on the right side of the Dock. A drag that misses by ten pixels resizes instead of opening.
• Magnification stays predictable. If you use hover magnification, a fixed base size keeps the zoom consistent instead of compounding a stray resize.
• Shared and family Macs stay tidy. Guests and kids can't turn your carefully sized Dock into a row of postage stamps — or a wall of billboards.
• Muscle memory holds. A Dock that never changes size keeps every icon in a stable position, which is most of what makes a Dock fast to use.

Part of a family of Dock locks

The Dock supports several -immutable switches, each freezing one property — combine them to taste:

# lock the Dock's screen position (bottom/left/right)
defaults write com.apple.dock position-immutable -bool true

# lock the auto-hide on/off state
defaults write com.apple.dock autohide-immutable -bool true

# lock the icons themselves — no adding or removing
defaults write com.apple.dock contents-immutable -bool true
killall Dock

Each is undone the same way: defaults delete com.apple.dock <key> followed by killall Dock. Size plus contents is the classic “set up the family Mac and walk away” combination.

Audit what's currently set

Six months from now, when the slider mysteriously “doesn't work,” you'll want to know whether past-you locked it. Query the keys:

# prints 1 if locked; errors if never set
defaults read com.apple.dock size-immutable

# current base icon size in points
defaults read com.apple.dock tilesize

An error reading a key just means it was never written — the default, unlocked state. And before experimenting with several Dock tweaks at once, take a snapshot you can restore: defaults export com.apple.dock ~/Desktop/dock-backup.plist saves everything, and defaults import com.apple.dock ~/Desktop/dock-backup.plist followed by killall Dock puts it all back exactly.

Going all the way?

If the goal is a Dock nobody can mess with at all, freeze the icons too — lock the Dock so apps can't be added or removed covers the contents lock and its companions.