Letter Grade to Percentage Converter (A–F Scale)

A letter grade names a band, not a number, so converting one back to a percentage is an inherently lossy operation. The three scales here cut the same 0 to 100 axis in different places. The standard plus and minus scale splits each ten point decade unevenly, giving A-minus 90 to 92, A 93 to 96 and A-plus 97 to 100, so the passing bands are three or four points wide. The ten point scale assigns one letter per decade with no subdivision. The seven point scale, still used in parts of the American South and in some private schools, raises every cut: B spans 85 to 92 and C spans 77 to 84. The practical consequence is that an identical 82 is reported as a B-minus, a B or a C depending only on which scale the school adopted. Because the inverse mapping returns a range, the midpoint shown here can be off by two to four points in either direction, and it is meaningless for F, which spans everything from 0 to 59. Grade point values attach to the bands rather than to the underlying percentage, which is why an A-minus at 3.7 and an A at 4.0 differ by 0.9 quality points in a three credit course despite representing scores that may be one point apart. No federal grading standard exists in the United States; scale selection sits with districts, institutions and often individual instructors, so a transcript letter should always be read against the issuing school's published key.

Letter grading is a nineteenth century American invention that replaced descriptive ranking. Yale used a four category Latin scheme under president Ezra Stiles in 1785, sorting students as optimi, second optimi, inferiores and pejores. Harvard experimented with numerical divisions through the nineteenth century and is generally credited with adopting letters in the 1880s. The version that spread nationally is usually traced to Mount Holyoke College, which in 1897 adopted an A through E scale in which E marked failure at anything below 75 percent. The letters proved portable across subjects in a way percentage marks did not, and by the 1920s they dominated American schooling. The later refinements were administrative rather than pedagogical. Plus and minus modifiers were added by institutions seeking finer discrimination for class rank and honors, which is also why the F band was left undivided; there is no purpose in ranking degrees of failure. Scale choice remains genuinely contested. North Carolina moved its public high schools from a seven point to a ten point scale beginning with the 2015-16 school year, explicitly to stop disadvantaging its graduates in scholarship and admissions comparisons against states already using the more generous decade bands, an unusually clear illustration that these cut points are policy decisions rather than measurements.