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102 LearnersLast updated on December 11, 2025

100111 in binary represents the number 39 in the decimal system. The binary system, using only two digits, 0 and 1, is fundamental to computer systems. In this topic, we explore the conversion and representation of 100111 in binary.
Converting 39 from decimal to binary involves dividing the number by 2.
Since binary uses only the digits 0 and 1, each division's quotient becomes the next dividend until the quotient is 0.
The remainders, noted from bottom to top, form the binary equivalent.
For 39, this process results in 100111.
The chart below shows the binary digits (1 and 0) for 100111.
The first column lists the binary digits, the second their place values, and the third the value calculation, where binary digits are multiplied by their corresponding place values.
Adding the results verifies 100111 in binary as 39 in decimal.
The conversion of 39 to binary can be achieved using several methods. Here are the steps for two common methods:
Expansion Method:
Step 1 - Determine the place values: In binary, each place value is a power of 2. Calculate these powers:
20 = 1
21 = 2
22 = 4
23 = 8
24 = 16
25 = 32
Since 32 is less than 39, we include it.
Step 2 - Identify the largest power of 2 less than or equal to 39: Start with 25 = 32, write 1 in the 25 place. Subtract 32 from 39: 39 - 32 = 7
Step 3 - Next largest power for the remainder 7 is 22 = 4: Write 1 in the 22 place, subtract 4: 7 - 4 = 3
Step 4 - The next largest power for 3 is 21 = 2: Write 1 in the 21 place, subtract 2: 3 - 2 = 1
Step 5 - Finally, 20 = 1 fits the remainder 1: Write 1 in the 20 place. The remainder is now 0.
Step 6 - Write 0 in unused places (24 and 23): Resulting binary is 100111.
Grouping Method:
Step 1 - Divide 39 by 2: 39 / 2 = 19, remainder 1
Step 2 - Divide 19 by 2: 19 / 2 = 9, remainder 1
Step 3 - Divide 9 by 2: 9 / 2 = 4, remainder 1
Step 4 - Divide 4 by 2: 4 / 2 = 2, remainder 0
Step 5 - Divide 2 by 2: 2 / 2 = 1, remainder 0
Step 6 - Divide 1 by 2: 1 / 2 = 0, remainder 1
Step 7 - Read remainders bottom to top: Binary is 100111.


To convert any number to binary, follow these rules:
Rule 1: Place Value Method Identify the largest power of 2 less than or equal to the number. Subtract the value and find the next power of 2 for the remainder. Continue until the remainder is 0, placing 0 in unused positions.
Rule 2: Division by 2 Method Divide the number by 2, recording the remainder. The quotient becomes the new dividend. Continue until the quotient is 0, writing remainders in reverse order.
Rule 3: Representation Method Break the number into powers of 2. Allocate 1s and 0s to appropriate powers of 2. Combine the digits to form the binary result.
Rule 4: Limitation Rule Only 0s and 1s represent numbers in binary. Each binary place represents a power of 2.
Some tips and tricks for understanding binary numbers:
Memorize binary forms for numbers 1 to 39 to speed up conversions.
Recognize patterns: 1 → 1, 1 + 1 = 2 → 10, 2 + 2 = 4 → 100, 4 + 4 = 8 → 1000, 8 + 8 = 16 → 10000, 16 + 16 = 32 → 100000
Even and odd rule: Even numbers in binary end in 0, odd numbers in 1.
Cross-verify conversions by converting back to decimal.
Practice with tables to remember conversions.
Common mistakes in converting numbers to binary:
Convert 39 from decimal to binary using the place value method.
100111
25 is the largest power of 2 less than 39.
Place 1 next to 25.
Subtract 32 from 39 to get 7.
The next largest is 22.
Place 1 next to 22.
Subtract 4 to get 3.
The next is 21.
Place 1 next to 21.
Subtract 2 to get 1.
Place 1 next to 20.
Unused powers (24, 23) get 0.
Resulting binary is 100111.
Convert 39 from decimal to binary using the division by 2 method.
100111
Divide 39 by 2.
Quotient is new dividend until it is 0.
Write remainders upside down to get 100111.
Convert 39 to binary using the representation method.
100111
Break 39 into powers of 2: 25, 22, 21, and 20.
Allocate 1s and 0s accordingly.
Combine to form binary 100111.
How is 39 written in decimal, octal, and binary form?
Decimal form - 39
Octal - 47
Binary - 100111
Decimal 39 is 47 in octal.
Divide 39 by 8: 39 / 8 = 4, remainder 7.
Next step: 4 / 8 = 0, remainder 4.
Write remainders reverse order: 47 is octal of 39.
Express 39 - 4 in binary.
10011
39 - 4 = 35. Convert 35 to binary.
Divide 35 by 2, recording remainders and reversing order to get 10011.

Hiralee Lalitkumar Makwana has almost two years of teaching experience. She is a number ninja as she loves numbers. Her interest in numbers can be seen in the way she cracks math puzzles and hidden patterns.
: She loves to read number jokes and games.






