base 9 is a positional numeral system with nine as its base. It uses 9 different digits for representing numbers. The digits for base 9 could be 0, 1, 2, 3, 4, 5, 6, 7, and 8.

conversion table

base 9	base 5	base 9	base 5
1	≈ 1	12	≈ 21
2	≈ 2	13	≈ 22
3	≈ 3	14	≈ 23
4	≈ 4	15	≈ 24
5	≈ 10	16	≈ 30
6	≈ 11	17	≈ 31
7	≈ 12	18	≈ 32
8	≈ 13	20	≈ 33
10	≈ 14	21	≈ 34
11	≈ 20	22	≈ 40