Marking a stack of quizzes is faster when you do not have to calculate a percentage for every paper. That is the idea behind the EZ grader chart: you set the total number of questions once, then read off what each possible number of wrong answers means as a percentage and, on many scales, as a letter grade.
Teachers have used sliding versions of this chart for years. The physical chart has a scale you line up with the test length. An online version does the same job on screen. Either way, the maths underneath is simple, and understanding it helps you use the chart accurately and explain grades to students and parents.
How the sliding scale works
Start with the total number of questions on the test. That is your denominator — the score every student is measured against.
For each student, count only the number wrong (or, in some classrooms, the number correct). The chart is usually organised by questions wrong because, when marking, it is often quicker to tally errors as you go and mark them on the paper.
Then find that wrong count on the scale for your test length. The chart shows the matching percentage. If your school uses letter grades, the chart or your grading scale then converts that percentage to a letter.
The calculation behind every row is the same: correct answers divided by total questions, multiplied by 100. The chart simply pre-calculates it for every possible wrong count so you do not have to repeat the division thirty times.
For background on how different scales set their letter boundaries, see how EZ grading scales work.
A worked example with a long test
Suppose a test has 200 questions and a student gets 21 wrong.
That means the student answered 179 correctly, because 200 − 21 = 179.
The percentage is 179 ÷ 200 = 89.5%.
On a standard scale where an A starts at 90%, that is a B — just below the 90% A threshold. It is a useful example of why the chart helps. Doing that division and comparison for every student in a large class would be slow and easy to mistype, while the chart gives you the row immediately once the test length is set.
Long tests produce many possible percentages, including halves and other fractions. Short tests produce bigger jumps between rows, which the next example shows.
A worked example with a short quiz
Now take a 20-question quiz where a student gets 3 wrong.
The student has 17 correct, and 17 ÷ 20 = 85%.
On the same standard scale, that would also be a B in many schools, although exact letter boundaries vary. The important point is the step size. On a 20-question quiz, each question is worth 5 percentage points. One more wrong answer drops the score from 85% to 80%. On a 200-question test, each question is worth half a percentage point, so scores change in much smaller steps.
That is why the same chart needs a different scale position for each test length. A wrong count means nothing until you know the total.
A simple classroom workflow
Set the chart or tool to the total number of questions before you start marking. Keep an answer key beside you and decide in advance how you will handle half marks, partially correct answers and blank responses, if your test includes them.
As you mark each paper, tally the wrong answers and write the total wrong, the correct count and the percentage on the paper in the same place each time. A consistent spot makes later recording into a gradebook faster and reduces transcription mistakes.
If you teach several classes sitting the same test, keep the chart set to that test length until all of them are done. Reset it deliberately when the test length changes, and double-check the first paper of the new set by hand. Most chart errors come from using the previous test's scale, not from the chart itself.
Rounding and half points
Percentages do not always land on whole numbers, as the 89.5% example shows. Schools handle rounding in different ways. Some round .5 up, some truncate, some record the decimal as it is, and some letter scales are written to include values such as 89.5 explicitly.
There is no single rule that applies everywhere. The honest approach is to follow your school or department policy, apply it consistently to every student, and be ready to explain it. If your policy is not written down, decide before you start marking a set, note the rule you used, and use it for the whole set. Changing the rule halfway through for scores near a boundary creates unfair differences between students marked early and late.
The same applies to half marks. If a question can earn half a mark, agree how that is recorded before converting to a percentage, because a simple wrong-count chart assumes whole questions.
Frequently asked questions
Do I count wrong answers or correct answers?
Either works, as long as you use the scale correctly. Many EZ grader charts are read by questions wrong, because that is what teachers tally while marking. The percentage comes from correct divided by total.
Does the chart decide the letter grade?
The chart gives the percentage. The letter comes from the grading scale your school uses, so the same percentage could be a different letter in another school.
What if my test has 30 questions but the chart shows a different length?
Do not use the wrong length. Set the chart or tool to 30 first, because percentages depend entirely on the total number of questions.
When you want the speed of the chart without carrying a physical slider, use the online EZ Grader — enter the total questions and the number wrong or correct, and it shows the percentage and grade instantly, ready to record for each paper in your class set.