A 70 percent grade is a C- letter grade. A letter grade C- means satisfactory or average performance in a class or on a test. Any percentage score in the 70-72.9 range is a C- on the grade scale table.
A 70 is a C- and is one percentage point above a D+. 70 is the lowest percent grade in the "C" letter range.
Aside from 70 out of 100, there are numerous ways students can end up with 70% grades. Here are scales for common number of test questions that can lead to a 70 grade.
If you are scoring in the 70% range on tests and assignment, you really need to be studying much harder if you're thinking about going to college. Check out the discussion about grade averages in this range (1.7 GPA) to see how you're doing.
Reference table of the percentage grade scale with letter grade and unweighted GPA point equivalents. This grade scale is used my most U.S. middle schools, high schools and colleges.