The posted arrangement is the tightest known packing of 17 squares. The outer square has a side length of 4.6756 times a small sqare’s. So unless you’ve just found one no mathematician has thought of since 1998 yours is slightly larger.

Edit:
I found this tool to play around and your packing is 4.7 https://markorastas.github.io/PackingProblem/

Edit edit:
I’m a dummy you just need pythagoras, yours is 4+√0.5≈4.7071