Docker Compose Memory Limits Calculator
Docker Compose's deploy.resources block controls how much memory a service reserves and how
much it's allowed to use before it gets killed. This calculator sizes both values — plus the service-level
mem_limit / mem_reservation equivalent — from your service's observed
average and peak memory usage.
01 Usage data
Which query should I paste?
Use a range query over a representative period (a week is a good default) for one service. Every sample is averaged, and the highest becomes the peak — an instant query only gives one value per container.
container_memory_working_set_bytes{name=~"myproject-api-[0-9]+"}
Compose names containers <project>-<service>-<number>, so this matches every replica of one service.
Paste the Prometheus UI table output, the HTTP API JSON, a Grafana CSV export, or a list of values with units (412 MiB).
Enter observed usage directly, in MiB.
02 Workload profile
Advanced: margins and defaults
Values the result relies on that are our own defaults, or vendor defaults your setup may change. Each “?” says how one moves the result; the guide says where it comes from.
03 Sizing gauge
04 docker-compose.yml
—05 How this was derived
How every number is calculated, with sources and assumptions (opens in a new tab) ↗
Result looks wrong? Report it
Limits, reservations and swap in short
The limit becomes the container's hard memory limit (--memory). The reservation becomes --memory-reservation: a soft limit, lower than the limit, that Docker enforces only when it detects contention or low memory on the host. Docker docs
The calculator sizes the reservation from the average and the limit from the peak, then adds margins that are MemoryLimit's own defaults, not vendor figures; you can change them under Advanced. Docker rejects a limit below its reservation, so when the peak is close to the average the limit is raised to the reservation. Docker source
Swap. If the host has swap and memswap_limit isn't set, a container with a memory limit can use as much swap as that limit. Setting memswap_limit equal to the limit prevents any swap. The calculator leaves swap as Docker sets it. Docker docs
Common input mistakes
- Sizing from total usage instead of the working set: total usage includes reclaimable file cache, so services that read many files get larger values.
- Filtering by the wrong container name: Compose names containers
<project>-<service>-<number>, and a service with its owncontainer_nameneeds that name in the query. - A window that misses the busiest times: the limit comes out too low.
Full derivation, warnings and every assumption: how the Docker Compose calculator works. The shared formula and margin tables: the sizing model.
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