How curving works
A grade curve adjusts raw scores, usually after a test that turned out harder than planned. Different methods change the scores in different ways, so the same raw score can end up at several different grades. This calculator applies five common methods to a score out of 100.
Methods and formulas
- Add flat points:
new = score + points - Highest score becomes 100 (add points):
new = score + (100 − highest score) - Highest score becomes 100 (scale):
new = score × 100 ÷ highest score - Square root curve:
new = 10 × √score - Bell curve:
new = new mean + (score − class mean) ÷ class standard deviation × new standard deviation
Curved scores are limited to 0–100%.
One score, five curves
Take a raw score of 70, a class high of 88, a class average of 62 with a standard deviation of 12, and a target average of 75 with a spread of 10.
| Method | New score | Letter |
|---|---|---|
| Add 5 flat points | 75% | C |
| Add points (top score to 100) | 82% | B |
| Scale (top score to 100) | 79.55% | C |
| Square root curve | 83.67% | B |
| Bell curve | 81.67% | B |
Letter grades
The calculator uses the common scale A 90+, B 80–89, C 70–79, D 60–69 and F below 60. Your school may use plus/minus grades or different cut-offs. To see how a final grade combines with other work, try the high school grade calculator.
Common mistakes
- Entering the class high as a percentage of a different total than your own score.
- Expecting every instructor to use the same curve.
- Forgetting that scores are capped at 100%.
How to use this calculator
- Enter your values. See how a curve changes your score and letter grade, using the most common curving methods.
- Check units and assumptions. Make sure the inputs use the same scale and that any optional settings match your situation.
- Calculate and review. Compare the output with the formula below and note any limitations stated on the page.
Formula and calculation method
Use the conversion scale or grading method selected by your institution. There is no universally applicable CGPA-to-percentage or CGPA-to-GPA conversion across all schools, so the institution’s published policy takes precedence.
Worked example
For example, if your university publishes a specific CGPA conversion formula, enter the value using that scale rather than assuming a different university’s formula applies. Keep the original scale and the converted result together when reporting grades.
Search and practical tips
People commonly search for a grade curve calculator – curved score tool, how to calculate the result step by step, which formula to use, and how to check the answer manually. Use the formula above as a transparent starting point, and consult the relevant institution, agency, or qualified professional when an official rule or personal circumstances affect the result.
Frequently asked questions
How do you curve grades?
Instructors pick a method and apply it to every score. Common methods add flat points, shift the class so the top score is 100, scale scores up, take a square root or reshape scores to a new average.
What is a square root curve?
The curved score is 10 times the square root of the original score. A 64 becomes 80 and a 36 becomes 60, so lower scores gain the most.
What is a bell curve?
A bell curve rescales scores so the class has a chosen average and spread. Scores are compared with the class average and standard deviation, so grades can go down as well as up.
Can a curve lower my grade?
The flat, highest-score and square root methods never lower a score. A bell curve can, because it reshapes scores around a new average and spread instead of only raising them.
Will my teacher use the same method?
Not necessarily. Instructors decide whether and how to curve, so treat the result as an estimate.