Docker Image Size Estimator

What is Docker Image Size Estimator?

Docker images are built from stacked layers — each FROM, RUN, COPY, and ADD instruction adds a layer. The total image size directly affects pull times, registry storage costs, deployment speed, and attack surface. This tool lets you estimate your final image size before building by combining a known base image with your own application layers, without needing Docker or a registry connection.

How to use this tool

1. 1 Select a base image from the dropdown — popular options like node:alpine, python:slim, and golang:alpine are pre-loaded with real size data.
2. 2 Or enter a custom base size if you know your exact base image's compressed and uncompressed sizes from Docker Hub.
3. 3 Click 'Add Layer' to model your application layers — source code copies, dependency installs, config files, and compiled binaries.
4. 4 For each layer enter the estimated compressed size (what gets transferred over the network) and uncompressed size (disk usage at runtime). If you only know one value, enter it and leave the other blank — the estimator will approximate.
5. 5 Read the total compressed and uncompressed sizes. The size banner benchmarks your image against best-practice thresholds and suggests optimisations.

When would you use this?

• Before writing a Dockerfile — choose the smallest viable base image by comparing sizes in the reference table.
• Evaluating whether to add a dependency — estimate how much a new apt-get install or npm install adds to your final image.
• Optimising CI/CD pipelines — large images slow every deployment. Use this tool to set a size budget before running the actual build.

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