The standard US grading scale is A 90–100, B 80–89, C 70–79, D 60–69, F below 60, often split into plus/minus bands. A curve raises raw scores before applying that scale — the three common methods are a flat add (same points for everyone), a square-root curve (10 × √score, helping low scores most), and a top-score curve (scaling so the class's highest score becomes 100%).
Key takeaways
- Standard scale: A 90+, B 80+, C 70+, D 60+, F < 60.
- Plus/minus bands split each letter (A− 90–92, B+ 87–89, …).
- Flat add: +N points to every score.
- Square-root: new = 10 × √raw; biggest lift for low scores.
- Top-score: raw × (100 ÷ class high); best score becomes 100%.
- Cutoffs and curve policy vary — confirm your class's.
The standard A–F scale
Most US classes map percentages to letters with 10-point bands, and many add a plus/minus tier inside each band:
| Letter | Percentage | With plus/minus | GPA points |
|---|---|---|---|
| A | 90–100% | A− 90–92, A 93–96, A+ 97–100 | 3.7–4.0 |
| B | 80–89% | B− 80–82, B 83–86, B+ 87–89 | 2.7–3.3 |
| C | 70–79% | C− 70–72, C 73–76, C+ 77–79 | 1.7–2.3 |
| D | 60–69% | D− 60–62, D 63–66, D+ 67–69 | 0.7–1.3 |
| F | Below 60% | F | 0.0 |
Plus/minus bands and exact cutoffs vary widely between schools — these are typical, not universal. The easy grader and percentage grade calculator use the simple 10-point scale; check your syllabus for the rest.
The three curve methods
A curve adjusts raw scores before the scale is applied, usually to offset a hard exam. The grade curve calculator applies each of these:
Worked example: a 72 on a hard test
Say you scored a 72, the class high was 88, and the teacher considers a curve:
- Flat add of 8: 72 + 8 = 80 (a B). Everyone rises 8 points.
- Square-root: 10 × √72 = 10 × 8.49 = 84.9 (a B). A 50 would jump to 70.7 — low scores gain the most.
- Top-score: 72 × (100 ÷ 88) = 72 × 1.136 = 81.8 (a B). The 88 becomes a 100.
Same raw score, three different curved results — which is why it matters to know which curve your teacher uses. None of these methods can lower a score.
Frequently asked questions
What are the standard A–F grade cutoffs?
Standard: A 90–100, B 80–89, C 70–79, D 60–69, F below 60. Plus/minus scales split each band further. Confirm your class’s exact cutoffs.
How does a grade curve work?
A curve lifts raw scores by a rule: flat add (same points for all), square-root (10 × √score, helps low scores most), or top-score (scale so the class’s best becomes 100%). The curve calculator applies all three.
Does curving always raise my grade?
With these common methods a curve never lowers your score; how much it helps depends on the method and your raw mark — square-root favors low scores, top-score helps proportionally.
Sources: the 10-point A–F scale and typical plus/minus bands reflect common US grading practice; the flat-add, square-root (10·√score), and top-score scaling methods are standard curving techniques. Exact cutoffs, plus/minus values, and whether (and how) a class curves are set by each teacher and school — confirm yours.
Last reviewed 2026-06-28