Answers above are great, but there is a low-tech solution for most cases – ncdu. This utility will show pretty and interactive tree structure with sizes. It has an option that will take patterns from a file and exclude them from scan. So you can just do ncdu -X .dockerignore. You will get something like this:
This is pretty close to what you will get in your docker image. One caveat is thou if you add a dot directory (like .yarn) into an image, it will not show in ncdu output.