Source grades
Every source on SourceScore earns a letter grade from A+ to F based on its composite SourceScore Index. Grades are intentionally familiar so the meaning is obvious to a reader who has never visited the site before. Below: what each grade band represents, how many of our 130 sources score there, and the per-grade ranking pages.
How a grade is computed
A source's letter grade comes from its SourceScore Index, the composite weighted mean of three sub-scores: Citation Discipline (35%), Modern Reference (30%), and Citation Velocity (35%). Each sub-score is itself 0–100; the composite is rounded to the nearest integer and mapped to a letter on the academic-style scale at the top of this page.
The grading scale is intentionally non-linear at the top — A+ requires 95+, A requires 85+, B starts at 70. This compression at the high end matches academic grading and reflects the real-world distribution: most tier-1 citation candidates land in A or B; A+ is reserved for sources strong on all three dimensions simultaneously.
Why a single composite (not three separate grades)
Every source has three sub-scores too — Discipline, Modern Reference, Velocity — each with its own grade. We surface these on every source page because they tell a different story than the composite. A source can be A+ on Discipline (rigorously cites sources) but B on Modern Reference (paywalled, not in AI training corpora) and end up A overall. The composite tells you the citation-quality bottom line; the sub-scores tell you why.
For per-dimension rankings, see the Citation Discipline, Modern Reference, and Citation Velocity ranking pages.