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Repeated division

Also called: division-remainder method, repeated division by 2, successive division

A method for converting a decimal number to another base: divide by the base again and again, and read the remainders from last to first.

Repeated division converts a decimal number into any base b. It's the standard method for decimal → binary, octal or hex.

  1. Divide the number by b. Write down the remainder (0 to b − 1).
  2. Replace the number with the quotient.
  3. Repeat until the quotient is 0.
  4. Read the remainders from last to first. The first remainder is the rightmost digit.

Why it works: dividing by 2 is like pairing things up. Whatever is left over after pairing is the 1s bit. Pair up the pairs, and the leftover is the 2s bit, and so on. The smallest bundle is found first, which is why the first remainder is the LSB.

For hex, divide by 16 and write remainders of 10–15 as the letters A–F. Each remainder is one digit, even if it's 12. For octal, divide by 8.

1
16
1
8
0
4
0
2
1
1

Worked examples

Example

25₁₀ to binary

Divide by 2 until the quotient is 0.

  1. 1.

    25 ÷ 2 = 12 remainder 1 (LSB)

  2. 2.

    12 ÷ 2 = 6 remainder 0

  3. 3.

    6 ÷ 2 = 3 remainder 0

  4. 4.

    3 ÷ 2 = 1 remainder 1

  5. 5.

    1 ÷ 2 = 0 remainder 1 (MSB)

  6. 6.

    Read last to first: 11001₂. Check: 16 + 8 + 1 = 25.

Example

300₁₀ to hex

The same method with 16 as the divisor.

  1. 1.

    300 ÷ 16 = 18 remainder 12, written C (rightmost digit).

  2. 2.

    18 ÷ 16 = 1 remainder 2.

  3. 3.

    1 ÷ 16 = 0 remainder 1.

  4. 4.

    Read last to first: 12C₁₆. Check: 256 + 32 + 12 = 300.

Common mistakes

  • Reading the remainders top-down.

  • Writing a hex remainder of 10–15 as two digits instead of one letter.

  • Stopping when the quotient reaches 1 instead of 0.

Practice Repeated division

Interactive questions with instant feedback and a worked solution for every wrong answer.

Learn it step by step

Repeated division is taught in Number Systems.