18 out of 21 as a percentage is 85.71% (B)

An 18/21 is 85.71%, which is a B on the standard grading scale. That is a 3.0 GPA, and you got 3 wrong.

Next grade1 more → A19 out of 21 is 90.48%

With a 5-point curve90.71% → Aif your teacher adds 5 points

To pass (60%)Passed13 out of 21 is the passing line

What an 18/21 grade means

18 correct and 3 wrong on a 21-question test.
Each question is worth 4.76%, so every wrong answer costs 4.76 percentage points.
Any score from 17 to 18 out of 21 is a B.
1 more correct (19 out of 21, 90.48%) would make it an A.
It passes a 60% passing score, which needs 13 out of 21.

Divide the score by the total: 18 ÷ 21 = 0.8571.
Multiply by 100: 0.8571 × 100 = 85.71%.
Find 85.71% on the grading scale: A is 90% and up, B 80%, C 70% and D 60%, so it is a B.

Rounded to a whole number this is 86%, and the letter grade stays the same.

Scale	Cutoffs	Letter	GPA
Standard A–F	A 90, B 80, C 70, D 60	B	3.0
Plus and minus	A 93, A− 90, B+ 87, B 83, B− 80 …	B	3.0
7-point	A 93, B 85, C 77, D 70	B	3.0

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

Every possible score out of 21, with 18 highlighted. Pick any score to see its page.

Correct	Wrong	Percentage	Grade
21	0	100%	A
20	1	95.2%	A
19	2	90.5%	A
18	3	85.7%	B
17	4	81%	B
16	5	76.2%	C
15	6	71.4%	C
14	7	66.7%	D
13	8	61.9%	D
12	9	57.1%	F
11	10	52.4%	F
10	11	47.6%	F
9	12	42.9%	F
8	13	38.1%	F
7	14	33.3%	F
6	15	28.6%	F
5	16	23.8%	F
4	17	19%	F
3	18	14.3%	F
2	19	9.5%	F
1	20	4.8%	F
0	21	0%	F

Yes. It is a B, a solid grade above the C average.

3.0 on a 4.0 scale, as a B.

With a half point, 18.5 out of 21 is 88.1%: a B on the standard scale and a B+ with plus and minus grades.

8 at most with a 60% passing score: you need 13 out of 21. With a 70% passing score you need 15 out of 21.