Thanks for reaching Q & A forum.
The size you see in Azure Portal or with az acr show-usage
is the size of all the images in a registry. We don't have support for each image size at this point.
Try with the CLI
$ az acr repository show-manifests --repository fatimage --detail --query '[].{Size: imageSize, Tags: tags}'
[
{
"Size": 4296278237,
"Tags": [
"4gb"
]
}
------
If this answers your query, do click Accept Answer
and Up-Vote for the same. And, if you have any further query do let us know.