googleさんがAIで教えてくれた

The Su-57 fighter jet's radar cross section (RCS) is estimated to be between 0.1 and 1 square meters.
This is about 30 times smaller than the RCS of the Su-27, which is around 10 to 15 square meters.

すごい！フランカーの30分の1ぐらいのRCSだって。ユーロファイターと変わらんがな