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