15 out of 21 as a percentage is 71.43% (C)

A 15/21 is 71.43%, 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 6 wrong.

Next grade2 more → B17 out of 21 is 80.95%

With a 5-point curve76.43% → Cif your teacher adds 5 points

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

What a 15/21 grade means

15 correct and 6 wrong on a 21-question test.
Each question is worth 4.76%, so every wrong answer costs 4.76 percentage points.
Any score from 15 to 16 out of 21 is a C.
2 more correct (17 out of 21, 80.95%) would make it a B.
It passes a 60% passing score, which needs 13 out of 21.

Divide the score by the total: 15 ÷ 21 = 0.7143.
Multiply by 100: 0.7143 × 100 = 71.43%.
Find 71.43% 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 71%, 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 21, with 15 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

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, 15.5 out of 21 is 73.81%: a C on the standard scale and a C 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.