// Docker Resource Constraints

Docker Memory Limit —
Calculator & Command Generator

Generate docker run -m and docker-compose memory flags instantly. Covers --memory, --memory-swap, --memory-reservation, and OOM kill settings.

--memory --memory-swap --memory-reservation docker-compose

Container name

Docker image

Memory limit

Memory swap (total mem+swap)

Set equal to --memory to disable swap. -1 = unlimited swap.

Memory reservation (soft limit)

Optional. Should be lower than --memory.

OOM kill

Docker memory limit guide

--memory vs --memory-reservation — what is the difference?
--memory (or -m) is a hard limit — the container cannot use more than this amount. If it tries to allocate more, the OOM killer terminates it. --memory-reservation is a soft limit — Docker will try to reclaim memory from the container when the host is under memory pressure, but the container can still exceed this value up to the hard limit. Use reservation for workloads that can tolerate some memory being reclaimed, and hard limit to absolutely cap a container's footprint.

--memory-swap explained
--memory-swap is the total memory + swap available to the container, not just the swap amount. If --memory=512m and --memory-swap=1g, the container can use 512MB RAM + 512MB swap. Set --memory-swap equal to --memory to disable swap entirely. Set to -1 for unlimited swap. If you set --memory without --memory-swap, Docker defaults to 2x memory for swap. On hosts without a swap partition, this flag has no effect.

What happens when a container exceeds its memory limit?
When a container's memory usage exceeds the hard limit, the Linux OOM (Out of Memory) killer terminates a process inside the container. This usually kills the main process, causing the container to exit. Docker will restart it if you have a restart policy (--restart always or --restart on-failure). You can disable OOM killing with --oom-kill-disable — but this can cause the host to hang if the container grows unbounded. Always combine --oom-kill-disable with a hard memory limit.

FAQ — Docker memory limits

Use the -m or --memory flag with docker run: docker run -m 512m nginx. For docker-compose, set memory under deploy.resources.limits.memory: 512m (Compose v3) or under mem_limit: 512m (Compose v2). Use the calculator above to generate the exact command for your configuration.

It depends on your workload. General guidance: run the container without a limit first and observe peak memory with docker stats CONTAINER_NAME. Add 20-30% overhead to the observed peak and set that as your limit. Common values: Node.js API: 256m-512m. Java/Spring Boot: 512m-1g (tune JVM heap with -Xmx to stay below the Docker limit). Nginx: 64m-128m. PostgreSQL: 256m-1g. Redis: 128m-256m. Always test under load before setting final limits.

In Compose v3 (deploy section, requires Swarm mode or docker compose): set deploy.resources.limits.memory and deploy.resources.reservations.memory. In Compose v2 (older): use mem_limit and memswap_limit directly under the service. Use the calculator above to get the exact YAML snippet for your values. Note: in standalone docker compose (not Swarm), the deploy section is honored since Compose v2.x.

Use docker stats to see live memory usage: docker stats CONTAINER_NAME or docker stats --no-stream for a one-time snapshot. The MEM USAGE / LIMIT column shows current usage vs the configured limit. For detailed memory breakdown: docker inspect CONTAINER_NAME | grep -i memory shows all memory settings. In Kubernetes, use kubectl top pod for equivalent metrics.

Docker Memory Limit —Calculator & Command Generator

Docker Memory Limit —
Calculator & Command Generator