GGB As a working rule, a healthy restaurant keeps prime cost somewhere in the mid-50s to low-60s as a share of revenue, and treats the mid-60s as a ceiling — but the figure varies by concept, which is the point of reading the sum rather than either line alone. The ranges are indicative; what matters is tracking your own number weekly against a deliberate target.
From Restaurant Prime Cost: The 60–65% Ceiling That Decides Survival — the full reading, with the method behind this answer.