Octal — base 8 — is the veteran number system of early computing, and it still surfaces every time a Unix user types chmod 755 and wonders what those digits mean. The conversion mirrors the binary method with an 8-flavored twist: divide by 8 repeatedly, keep each remainder (0–7), and read them bottom-to-top. For 64: 64 ÷ 8 is 8 remainder 0, then 8 ÷ 8 is 1 remainder 0, giving 100₈. This calculator lays out the gears: the Decimal Number box takes your input, the ÷ 8 (quotient) and mod 8 (last octal digit) boxes show each division step, and the 8¹ place value box tracks the positional math. Each octal digit maps to exactly three bits, which is why file permissions group bits in threes — 7 is rwx, 5 is r-x, and suddenly chmod makes sense. Old-school programmers, embedded engineers, and Linux admins still read octal fluently; this page is the fastest way to join them.

With the pre-filled defaults — Decimal Number 64 — the Decimal to Octal returns ÷ 8 (quotient) 8, mod 8 (last octal digit) 0, 8¹ place value 64. Change any input and those results update instantly, so you can see exactly how each number you enter moves the answer.