A displayed percentage can round up while the unrounded score remains below a cutoff.
Your grade chart
The chart uses the question count and cutoffs above.
From wrong answers to a percentage
Subtract wrong answers from the total, then divide the correct answers by the total. Each question must be worth the same number of points.
Score % = (questions − wrong) ÷ questions × 100
Three wrong out of 25 leaves 22 correct. That is 88%. If a half-correct response earns half credit, count it as half wrong.
For questions with different point values, enter total points instead, or use the points grade calculator for several assignments.
Set the cutoffs before marking papers
The percentage is arithmetic. The letter depends on your class scale. Choose a named scale or enter your own cutoffs; use the rounding option only if it matches your policy.
The downloaded chart contains wrong answers, correct answers, percentages and letters. It contains no student names. Printing uses a plain table and keeps the selected scale with the chart.
If you need to change a whole class's scores, compare the arithmetic in the grade curve calculator. Changing cutoffs in the grading scale tool is a different policy choice.