13 out of 18 as a percentage is 72.22% (C)

A 13/18 is 72.22%, which is a C on the standard grading scale (a C− with plus and minus grades). That is a 2.0 GPA, and you got 5 wrong.

Next grade2 more → B15 out of 18 is 83.33%

With a 5-point curve77.22% → Cif your teacher adds 5 points

To pass (60%)Passed11 out of 18 is the passing line

What a 13/18 grade means

13 correct and 5 wrong on a 18-question test.
Each question is worth 5.56%, so every wrong answer costs 5.56 percentage points.
Any score from 13 to 14 out of 18 is a C.
2 more correct (15 out of 18, 83.33%) would make it a B.
It passes a 60% passing score, which needs 11 out of 18.

Divide the score by the total: 13 ÷ 18 = 0.7222.
Multiply by 100: 0.7222 × 100 = 72.22%.
Find 72.22% on the grading scale: A is 90% and up, B 80%, C 70% and D 60%, so it is a C.

Rounded to a whole number this is 72%, and the letter grade stays the same.

Scale	Cutoffs	Letter	GPA
Standard A–F	A 90, B 80, C 70, D 60	C	2.0
Plus and minus	A 93, A− 90, B+ 87, B 83, B− 80 …	C−	1.7
7-point	A 93, B 85, C 77, D 70	D	1.0

Which scale applies depends on your school or teacher; the syllabus usually says. The grading scales guide compares them.

Every possible score out of 18, with 13 highlighted. Pick any score to see its page.

Correct	Wrong	Percentage	Grade
18	0	100%	A
17	1	94.4%	A
16	2	88.9%	B
15	3	83.3%	B
14	4	77.8%	C
13	5	72.2%	C
12	6	66.7%	D
11	7	61.1%	D
10	8	55.6%	F
9	9	50%	F
8	10	44.4%	F
7	11	38.9%	F
6	12	33.3%	F
5	13	27.8%	F
4	14	22.2%	F
3	15	16.7%	F
2	16	11.1%	F
1	17	5.6%	F
0	18	0%	F

It is a C, an average grade and a pass at most US schools. On a stricter 7-point scale it would be a D.

2.0 on a 4.0 scale as a C, or 1.7 if your school uses plus and minus grades (C−).

With a half point, 13.5 out of 18 is 75%: a C on the standard scale and a C with plus and minus grades.

7 at most with a 60% passing score: you need 11 out of 18. With a 70% passing score you need 13 out of 18.