Square Root Curve Calculator
The square root curve (sometimes called the Texas curve) replaces a raw percentage with 10 × its square root — a 64 becomes an 80. Enter a raw score to see the curved grade.
Example: with Raw score (points earned) 64 · Points possible 100 → Curved grade: 80% (B-).
Computed by the calculator below using its default values. Change any input to see your own numbers.
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Check it outHow the square root curve works
Take the raw percentage, square-root it, and multiply by 10 — equivalently, √(raw ÷ max) × 100. A 64% becomes √64 × 10 = 80%; a 49% becomes 70%. The curve never lowers a score (100 stays 100) and it preserves rank order, but it helps struggling students most: a 36 gains 24 points (36 → 60) while an 81 gains only 9 (81 → 90).
It’s one of several ways teachers curve grades. A flat curve adds the same points to everyone, often 100 minus the top score. Grading on a bell curve instead fits scores to a target distribution — say, centering the class average on a C+ — so each letter depends on rank in the class, not just your own percentage. The square root curve stays popular because it needs no class statistics and works for a single student.
How it’s calculated
Curved percentage = √(raw score ÷ points possible) × 100, identical to 10 × √(raw percent) on a 100-point test. The boost row shows curved minus raw percentage points. Letters use the common US scale (A+ 97–100, A 93–96, A− 90–92, B+ 87–89, B 83–86, B− 80–82, C+ 77–79, C 73–76, C− 70–72, D+ 67–69, D 63–66, D− 60–62, F below 60).
Results update as you type and are estimates, not professional advice — verify important decisions with a qualified professional.
Common mistakes
- Curving raw points on a non-100-point test without converting — the curve applies to the percentage (this tool divides by points possible first).
- Applying the curve twice — square-root-curving an already-curved 80 inflates it to about 89.
- Expecting any score to pass — you still need a raw 36% to curve up to 60%.
Frequently asked questions
What does a 64 curve to with the square root curve?
√64 = 8, times 10 is 80 — so a 64 becomes an 80, jumping from a D to a B− on the standard scale.
How do you curve a test with the square root method?
Divide the raw score by the points possible, take the square root, and multiply by 100. An 18/25 is 72% raw, and √0.72 × 100 ≈ 84.9% curved.
Is the square root curve the same as a bell curve?
No. The square root curve transforms each score with a fixed formula; a bell curve regrades the whole class against a normal distribution, so your grade depends on everyone else’s.
How do teachers curve grades by adding points?
A flat curve adds the gap between 100 and the highest score to everyone — if the top score was 92, every student gains 8 points.
Can a curved grade go over 100?
Only if the raw score does (extra credit): √1.05 × 100 ≈ 102.5%. For raw scores at or below 100, the curve tops out at 100.