Docker system prune on Mac, explained.

Where Docker stores data on a Mac

Docker Desktop runs Linux in a small virtual machine, and that machine's disk is a single file. Every image you pull, every container, every volume, and all your build cache live inside it.

Sizes are from one developer Mac in October 2026. Two commands tell you what's really there:

docker system df
du -h ~/Library/Containers/com.docker.docker/Data/vms/0/data/Docker.raw

docker system df breaks usage into images, containers, local volumes, and build cache, with a RECLAIMABLE column for what nothing is using. Add -v for a line per image and volume.

What docker system prune deletes

By default, docker system prune removes:

• Stopped containers. Anything you ran and didn't remove. Running containers stay.
• Unused networks. Networks no container is attached to.
• Dangling images. Untagged layers left behind when you rebuild or pull a newer tag. Tagged images stay.
• Unused build cache. Layers BuildKit saved to make the next build faster.

Is it safe? For the default command, yes. Everything it removes can be pulled or rebuilt; the cost is a slower next build. Two flags change that. -a removes every image no container uses, so you'll download them again. --volumes removes unused anonymous volumes, and a volume may be the only copy of a local database. Use it only when you know what's in them.

How to clear Docker cache, flag by flag

docker system prune                 # stopped containers, unused networks, dangling images, build cache
docker system prune -a              # plus every image no container uses
docker system prune --volumes       # plus unused anonymous volumes (data)
docker builder prune                # build cache only
docker builder prune -a             # all build cache, not just dangling
docker image prune -a               # unused images only
docker volume prune                 # unused anonymous volumes only

• -f skips the confirmation prompt. Leave it off when you type the command yourself.
• --filter "until=24h" keeps anything created in the last day, which is handy when you want old layers gone but today's builds kept.
• docker builder prune is the answer to “clear Docker cache” when you mean build cache. It leaves images and containers alone.

If you really want to start over, Docker Desktop's Troubleshoot screen has Clean / Purge data, which erases every image, container, and volume. That's the supported way to empty Docker.raw.

How much disk space Docker uses

It depends on what you pull. A few base images and a database take a few gigabytes; a year of rebuilding multi-stage images can take tens. On the developer Mac above, Docker held 27.4 GB of images, and 15.4 GB of that was unused by any container. Volumes were 2.8 GB, half of it unused.

The file grows up to the disk limit set in Docker Desktop's Settings › Resources. Changing that limit can make Docker Desktop recreate the disk image, which erases everything in it, so read its warning before you apply. Prune first; Docker Desktop hands the freed space back to macOS, though du can take a few minutes to show it.

Don't delete Docker.raw

Moving Docker.raw to the Trash deletes every image, container, and volume at once, and Docker Desktop makes a new empty one. If that's what you want, use Clean / Purge data instead, so Docker does it cleanly.

Docker is also one of the usual reasons System Data looks huge in Storage settings. More caches: every tool's cache, one page each.