Grade from number of errors
Three errors on a 25-question quiz leave 22 correct, which is 88% and a B. Enter the total and the number wrong, and you get the correct count, the percentage and the letter on a fixed A to F scale. Free in your browser.
- Free
- Runs in your browser
- No sign-up
- Your data stays on your device
Run — free
Worked example
- Total items
- 25
- Errors
- 3
- Decimal places
- 2
- Correct items
- 22
- Percentage
- 88
- Letter grade
- B
Turn an error count into a clear assignment result without counting correct answers by hand. Enter the total number of equally weighted items and the number answered incorrectly. The calculator subtracts errors from the total, converts the correct share to a percentage, and assigns a conventional A, B, C, D, or F letter grade. It also reports the correct-item count, making the result easy to check, copy into a gradebook, or explain to a student.
Enter the assignment total and the error count
Start with the total number of items that can earn credit on the assignment, then enter how many of those items were incorrect. Every item is treated as equally weighted, so this calculator is appropriate for quizzes, spelling tests, worksheets, multiple-choice exams, and other work where each question contributes the same amount. The total must be a positive whole number, while errors may be zero or any whole number up to that total.
For example, an assignment with 25 questions and 3 errors has 22 correct items. Do not enter points deducted, penalty percentages, or a weighted category in the errors field, because those represent different grading rules. The optional decimals setting controls how many decimal places are displayed in the percentage; it does not change the underlying performance used to choose the letter grade.
Understand the percentage and letter calculation
With 3 errors out of 25 items, the calculation is 22 divided by 25, producing 88 percent. The letter grade uses a conventional fixed scale: A begins at 90 percent, B at 80, C at 70, D at 60, and F covers results below 60. Boundaries are evaluated from the unrounded percentage, which avoids promoting a result merely because its displayed value rounds upward.
For instance, a raw score just below 90 percent remains a B even when a zero-decimal display shows 90. The percentage is rounded half up only for presentation, from zero through four decimal places as requested. This separation between classification and display makes repeated calculations predictable and prevents formatting preferences from silently changing a student’s letter grade.
Always compare the fixed scale with the grading policy that actually governs the class.
Use the result responsibly in a grading workflow
The returned result includes the original total and error count, the derived correct-item count, the displayed percentage, and the letter grade. Keeping all five values together creates a compact audit trail: a teacher or student can reconstruct the arithmetic without guessing what was entered. The calculator is deterministic and does not use a network service, stored profile, current date, or random value, so identical inputs always produce identical outputs.
However, the fixed scale does not include plus or minus grades, curves, partial credit beyond item-level points, dropped questions, weighted sections, extra credit, or a school-specific cutoff table. Apply those policies separately or choose a calculator designed for them. Before publishing a grade, confirm that the assignment total is final, that omitted or bonus questions were handled consistently, and that the institution uses the stated A–F thresholds.
What you can do with it
Mark a classroom quiz
Convert each student’s mistake count into correct items, a percentage, and a conventional letter grade.
Check a returned assignment
Verify the percentage written on a worksheet by entering its total questions and marked errors.
FAQ
Which letter-grade scale is used?
A is 90 percent or higher, B is 80–89.999…, C is 70–79.999…, D is 60–69.999…, and F is below 60 percent.
Does rounding change the letter grade?
No. The letter is selected from the unrounded percentage; decimals only control the displayed percentage.
Does this calculator support plus and minus grades?
No. It returns only A, B, C, D, or F using the fixed thresholds described above.
What grade is 3 wrong out of 25?
It is 88 percent and a B. Taking 3 errors from 25 items leaves 22 correct, and 22 divided by 25 gives 88 percent, which sits in the B band that starts at 80.
Can I use it when questions are worth different points?
Only if every point behaves like one equal item. The calculator treats each item as equally weighted, so do not enter points deducted or penalty percentages as errors; a weighted test follows a different grading rule.
Related tools
For developers — API access
Everything on this page is available programmatically. This section is for teams who want to wire it into their own systems; everyone else can just use the tool above.
API endpoint
Prefer to automate it? One authenticated POST creates the task; the result comes back by webhook or a signed link. The same capability also runs here on the web, by email and from Telegram — and soon from our app too.
Call it from your stack
curl -X POST https://api.kit.forhosting.com/edu/grade-from-errors \
-H "Authorization: Bearer $KIT_KEY" \
-H "Content-Type: application/json" \
-d '{"total_items":25,"errors":3}'const res = await fetch("https://api.kit.forhosting.com/edu/grade-from-errors", {
method: "POST",
headers: {
"Authorization": `Bearer ${process.env.KIT_KEY}`,
"Content-Type": "application/json"
},
body: JSON.stringify({
"total_items": 25,
"errors": 3
})
});
const { task_id } = await res.json();import os, requests
res = requests.post(
"https://api.kit.forhosting.com/edu/grade-from-errors",
headers={"Authorization": f"Bearer {os.environ['KIT_KEY']}"},
json={
"total_items": 25,
"errors": 3
},
)
task_id = res.json()["task_id"]<?php
$res = file_get_contents("https://api.kit.forhosting.com/edu/grade-from-errors", false, stream_context_create([
"http" => [
"method" => "POST",
"header" => "Authorization: Bearer " . getenv("KIT_KEY") . "\r\nContent-Type: application/json",
"content" => '{"total_items":25,"errors":3}',
],
]));
$task = json_decode($res, true);body := bytes.NewBufferString(`{"total_items":25,"errors":3}`)
req, _ := http.NewRequest("POST", "https://api.kit.forhosting.com/edu/grade-from-errors", body)
req.Header.Set("Authorization", "Bearer "+os.Getenv("KIT_KEY"))
req.Header.Set("Content-Type", "application/json")
res, _ := http.DefaultClient.Do(req)Example request
{
"total_items": 25,
"errors": 3
}Example response
{
"task_id": "tsk_a1b2c3d4e5f6a1b2c3d4e5f6",
"type": "edu.grade_from_errors",
"status": "queued",
"_links": {
"result": "/tasks/tsk_…/result"
}
}The API is asynchronous: the call returns a task_id immediately and the result arrives by webhook. Polling is capped at 1 req/s per task.
Pricing
Published price — no tokens, no invented credits. A failed task is never charged.
Errors
| HTTP | Code | Meaning |
|---|---|---|
401 | unauthorized | Missing or invalid API key. |
402 | insufficient_balance | Your balance doesn't cover the task price. |
404 | unknown_type | That task type doesn't exist. |
429 | rate_limited | Too many requests. Use the webhook instead of polling. |
Technical notes
Enter the assignment total and the error count
If a question is worth several points, use the total possible points as total_items and the lost points as errors only when every point behaves like one equal item.
Understand the percentage and letter calculation
The calculator first subtracts errors from total_items to obtain correct_items. It then divides correct_items by total_items and multiplies by 100.
Use the result responsibly in a grading workflow
It works well for quick checks in the browser and for automated gradebook preparation through the API from $0.002 per request.
Integration use cases
Prepare gradebook imports
Use the API to produce consistent percentage and letter fields from stored error counts.
Technical questions
What formula converts errors into a percentage?
The calculator uses ((total_items - errors) / total_items) × 100.
Can the error count be greater than the total?
No. Both values must be whole numbers, and errors cannot exceed total_items.
How much does API access cost?
API access starts from $0.002 per request, while the browser calculator is free to use.