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Docker Container Density Calculator

Determine how many containers can run per host given CPU, memory and overhead.

About Docker Container Density Calculator

Container density is limited by whichever resource (CPU or memory) runs out first. Formula: maxContainers = min(availableCPU/cpuPerContainer, availableMemory/memoryPerContainer), after reserving resources for the OS and Docker daemon.

Formula

Max Containers

max = min(availableCPU / cpuPerContainer, availableMemory / memPerContainer)

availableCPU
Host CPU minus system reserve
cpuPerContainer
CPU allocated per container
availableMemory
Host memory minus reserve
memPerContainer
Memory per container

Worked example

With the default values below, Docker Container Density Calculator returns Max Containers per Host of 57. Change any input above and every figure here is recalculated in your browser.

Inputs used

Host CPU Coresaccepts 1–1,024 cores
16 cores
Host Memoryaccepts 1–16,384 GB
64 GB
CPU per Containeraccepts 0.01–128 cores
0.25 cores
Memory per Containeraccepts 1–1,048,576 MB
256 MB
System Reservedaccepts 0–50 %
10 %

Results

Max Containers per Host
57
Limiting Resource
CPU
Max by CPU
57
Max by Memory
230

Step by step

  1. 1Available CPU after system reserve= 14.4 cores
  2. 2Available memory after reserve= 57.6GB
  3. 3Max containers by CPU= 57
  4. 4Max containers by memory= 230

Assumptions and limits

  • The result is derived only from the 5 inputs listed above. Anything not among them is not part of the calculation.
  • In particular, this calculator does not take inflation, tax, fees or charges or compounding frequency into account.
  • Figures are rounded for display to whole numbers, so totals built from several rounded parts can differ slightly from the unrounded arithmetic.

How these calculators are built and tested is described on the Methodology page. If a figure looks wrong, please report it.

Frequently Asked Questions

Should I set CPU limits equal to requests?

For predictable density planning yes, but in practice many teams set limits higher than requests to allow bursting when other containers are idle, improving utilization at the cost of predictability.

What about PID limits?

Linux kernels have a default PID limit (~32768) shared across all containers. Very high container density with many threads per container can hit this before CPU/memory limits.

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