Adding docker image size to the action's summary

[y-nk]

I'd like to know if it was possible to consider adding the size (in Mb/Gb) of the image(s) built in the github action summary?

[Samielakkad]

At the moment this is not a built-in docker/build-push-action summary field. The action exposes imageid, digest, and metadata; the size shown for the downloadable .dockerbuild record is the build-record artifact size, not the published image size.

For a pushed image, you can append the compressed registry size yourself. One important detail: for a multi-platform image there is no single runtime image size, so report each platform. Also, do not sum the size fields in the top-level image index; those are manifest-document sizes, not layer bytes.

- name: Build and push
  id: build
  uses: docker/build-push-action@v7
  with:
    push: true
    platforms: linux/amd64,linux/arm64
    tags: ${{ env.IMAGE }}:${{ github.sha }}

- name: Add published image size to summary
  shell: bash
  env:
    IMAGE: ${{ env.IMAGE }}:${{ github.sha }}
    DIGEST: ${{ steps.build.outputs.digest }}
  run: |
    set -euo pipefail

    ref="${IMAGE}@${DIGEST}"
    root_manifest="$(docker buildx imagetools inspect "$ref" --raw)"

    manifest_bytes() {
      docker buildx imagetools inspect "$1" --raw \
        | jq '[(.config.size // 0), (.layers[]?.size // 0)] | add'
    }

    format_mib() {
      awk -v bytes="$1" 'BEGIN { printf "%.2f MiB", bytes / 1048576 }'
    }

    {
      echo '### Published image size'
      echo

      if jq -e '.manifests? | type == "array"' >/dev/null <<<"$root_manifest"; then
        echo '| Platform | Compressed size |'
        echo '|---|---:|'
        while IFS=$'\t' read -r platform digest; do
          bytes="$(manifest_bytes "${IMAGE}@${digest}")"
          echo "| \`${platform}\` | $(format_mib "$bytes") |"
        done < <(
          jq -r '
            .manifests[]
            | select(.platform.os? != null and .platform.os != "unknown")
            | [
                ([.platform.os, .platform.architecture, .platform.variant]
                  | map(select(. != null and . != "")) | join("/")),
                .digest
              ]
            | @tsv
          ' <<<"$root_manifest"
        )
      else
        bytes="$(jq '[(.config.size // 0), (.layers[]?.size // 0)] | add' <<<"$root_manifest")"
        echo "- \`${ref}\`: **$(format_mib "$bytes")**"
      fi

      echo
      echo '_Compressed registry bytes (config + layers), not uncompressed local disk usage._'
    } >> "$GITHUB_STEP_SUMMARY"

This measures the immutable digest and handles both a single-platform manifest and a multi-platform index. The platform.os == "unknown" filter excludes BuildKit attestation manifests.

If you use load: true, docker image inspect --format '{{.Size}}' is a different metric: the uncompressed local image size. The registry approach above is for push: true and reports the compressed bytes users download.

Sources: build-push-action outputs, current summary fields, and imagetools inspect --raw.

[y-nk]

@Samielakkad thank you for taking the time to answer. I know this already (ai helped) and rather requested that this custom script would be built-in. I think it's meaningful addition to the repo's code.