What compression level is best for flying?

Across the reviewers we read, 15-20 mmHg is the most commonly recommended range for general travel and long flights—it's enough graduated support to reduce swelling without being hard to put on. Firmer 20-30 mmHg socks come up for people prone to significant leg swelling or with medical guidance, but several travel-community threads note they're noticeably harder to pull on. If you have a clotting risk or medical condition, the consensus is to ask a doctor before going firmer.