Summarize this article:
Last updated on August 22, 2025
105 in binary is written as 1101001 because the binary system uses only two digits, 0 and 1, to represent numbers. This number system is widely used in computer systems. In this topic, we are going to learn about the binary representation of 105.
The process of converting 105 from decimal to binary involves dividing the number 105 by 2. Here, it is divided by 2 because the binary number system uses only two digits (0 and 1). The quotient becomes the dividend in the next step, and the process continues until the quotient becomes 0.
This is a commonly used method to convert 105 to binary. In the last step, the remainder is noted down bottom side up, and that becomes the converted value. For example, the remainders noted down after dividing 105 by 2 until getting 0 as the quotient is 1101001. Remember, the remainders here have been written upside down.
In the table shown below, the first column shows the binary digits (1 and 0) as 1101001. The second column represents the place values of each digit, and the third column is the value calculation, where the binary digits are multiplied by their corresponding place values.
The results of the third column can be added to cross-check if 1101001 in binary is indeed 105 in the decimal number system.
105 can be converted easily from decimal to binary. The methods mentioned below will help us convert the number. Let’s see how it is done.
Expansion Method: Let us see the step-by-step process of converting 105 using the expansion method.
Step 1 - Figure out the place values: In the binary system, each place value is a power of 2. Therefore, in the first step, we will ascertain the powers of 2. 20 = 1 21 = 2 22 = 4 23 = 8 24 = 16 25 = 32 26 = 64 Since 64 is less than 105, we stop at 26 = 64.
Step 2 - Identify the largest power of 2: In the previous step, we stopped at 26 = 64. This is because, in this step, we have to identify the largest power of 2, which is less than or equal to the given number, 105. Since 26 is the number we are looking for, write 1 in the 26 place. Now the value of 26, which is 64, is subtracted from 105. 105 - 64 = 41.
Step 3 - Identify the next largest power of 2: In this step, we need to find the largest power of 2 that fits into the result of the previous step, 41. So, the next largest power of 2 is 25 = 32. Write 1 in the 25 place. Subtract 32 from 41. 41 - 32 = 9.
Step 4 - Continue with smaller powers: Next, find the largest power of 2 that fits into 9, which is 23 = 8. Write 1 in the 23 place. Subtract 8 from 9. 9 - 8 = 1.
Step 5 - Continue to the smallest power: The last remaining value is 1, which is 20. Write 1 in the 20 place. Subtract 1 from 1. 1 - 1 = 0. We need to stop the process here since the remainder is 0.
Step 6 - Identify the unused place values: In the previous steps, we wrote 1s in the 26, 25, 23, and 20 places. Now, we can just write 0s in the remaining places, which are 24 and 22. Now, by substituting the values, we get: 0 in the 24 place 0 in the 22 place
Step 7 - Write the values in reverse order: We now write the numbers upside down to represent 105 in binary. Therefore, 1101001 is 105 in binary.
Grouping Method: In this method, we divide the number 105 by 2. Let us see the step-by-step conversion.
Step 1 - Divide the given number 105 by 2. 105 / 2 = 52. Here, 52 is the quotient and 1 is the remainder.
Step 2 - Divide the previous quotient (52) by 2. 52 / 2 = 26. Here, the quotient is 26 and the remainder is 0.
Step 3 - Repeat the previous step. 26 / 2 = 13. Now, the quotient is 13, and 0 is the remainder.
Step 4 - Repeat the previous step. 13 / 2 = 6. Here, the quotient is 6, and 1 is the remainder.
Step 5 - Repeat the previous step. 6 / 2 = 3. Here, the quotient is 3, and 0 is the remainder.
Step 6 - Repeat the previous step. 3 / 2 = 1. Here, the quotient is 1, and 1 is the remainder.
Step 7 - Repeat the previous step. 1 / 2 = 0. Here, the remainder is 1. And we stop the division here because the quotient is 0.
Step 8 - Write down the remainders from bottom to top. Therefore, 105 (decimal) = 1101001 (binary).
There are certain rules to follow when converting any number to binary. Some of them are mentioned below:
This is one of the most commonly used rules to convert any number to binary. The place value method is the same as the expansion method, where we need to find the largest power of 2. Let’s see a brief step-by-step explanation to understand the first rule. Find the largest power of 2 less than or equal to 105. Since the answer is 26, write 1 next to this power of 2. Subtract the value (64) from 105. So, 105 - 64 = 41. Find the largest power of 2 less than or equal to 41. The answer is 25. So, write 1 next to this power. Now, 41 - 32 = 9. Continue with 9, the largest power of 2 is 23. Write 1 next to it. 9 - 8 = 1. The largest power of 2 for 1 is 20. Write 1 next to it. Since there is no remainder, we write 0 next to the remaining powers (24 and 22). Final conversion will be 1101001.
The division by 2 method is the same as the grouping method. A brief step-by-step explanation is given below for better understanding. First, 105 is divided by 2 to get 52 as the quotient and 1 as the remainder. Now, 52 is divided by 2. Here, we will get 26 as the quotient and 0 as the remainder. Dividing 26 by 2, we get 13 as the quotient and 0 as the remainder. Divide 13 by 2 to get 6 as the quotient and 1 as the remainder. Divide 6 by 2 to get 3 as the quotient and 0 as the remainder. Divide 3 by 2 to get 1 as the quotient and 1 as the remainder. Divide 1 by 2 to get 1 as the remainder and 0 as the quotient. We stop the division once the quotient becomes 0. Now, we write the remainders upside down to get the binary equivalent of 105, 1101001.
This rule also involves breaking the number into powers of 2. Identify the powers of 2 and write them down in decreasing order i.e., 26, 25 ,24, 23, 22, 21, and 20. Find the largest power that fits into 105. Repeat the process and allocate 1s and 0s to the suitable powers of 2. Combine the digits (0 and 1) to get the binary result.
The limitation of the binary system is that only 0s and 1s can be used to represent numbers. The system doesn’t use any other digits other than 0 and 1. This is a base 2 number system, where the binary places represent powers of 2. So, every digit is either a 0 or a 1. To convert 105, we use 0s for 24 and 22, and 1s for 26, 25, 23, and 20
Learning a few tips and tricks is a great way to solve any mathematical problems easily. Let us take a look at some tips and tricks for binary numbers up to 105.
Here, let us take a look at some of the most commonly made mistakes while converting numbers to binary.
Convert 105 from decimal to binary using the place value method.
1101001
26 is the largest power of 2, which is less than or equal to 105.
So place 1 next to 26.
Subtracting 64 from 105, we get 41.
So the next largest power would be 25.
So place another 1 next to 25.
Now, subtracting 32 from 41, we get 9.
The largest power of 2 for 9 is 23.
Place 1 next to 23.
Subtract 8 from 9, leaving 1.
The largest power of 2 for 1 is 20.
Place 1 next to 20.
Now, we just place 0s in the remaining powers of 2, which are 24 and 22.
By using this method, we can find the binary form of 105.
Convert 105 from decimal to binary using the division by 2 method.
1101001
Divide 105 by 2. In the next step, the quotient becomes the new dividend.
Continue the process until the quotient becomes 0.
Now, write the remainders upside down to get the final result.
Convert 105 to binary using the representation method.
1101001
Break the number 105 into powers of 2 and find the largest powers of 2.
We get 26.
So 1 is placed next to 26.
Next, 105 - 64 = 41.
Now, the largest power of 2 is 25.
Once again, 1 is placed next to 25. 41 - 32 = 9.
The largest power of 2 for 9 is 23.
Place 1 next to 23. 9 - 8 = 1.
The largest power of 2 for 1 is 20.
Place 1 next to 20.
After getting 0, fill in with zeros for unused powers of 2.
By following this method, we get the binary value of 105 as 1101001.
How is 105 written in decimal, octal, and binary form?
Decimal form - 105 Octal - 151 Binary - 1101001
The decimal system is also called the base 10 system.
In this system, 105 is written as 105 only.
We have already seen how 105 is written as 1101001 in binary.
So, let us focus on the octal system, which is base 8.
To convert 105 to octal, we need to divide 105 by 8.
So 105 / 8 = 13 with 1 as the remainder. In the next step, divide the quotient from the previous step (13) by 8.
So 13 / 8 = 1 with 5 as the remainder.
The division process stops here because the quotient is now 0.
Here, 1, 5, and 1 are the remainders, and they have to be written in reverse order.
So, 151 is the octal equivalent of 105.
Express 105 - 5 in binary.
1000000
105 - 5 = 100 So, we need to write 100 in binary.
Start by dividing 100 by 2.
We get 50 as the quotient and 0 as the remainder.
Next, divide 50 by 2.
Now we get 25 as the quotient and 0 as the remainder.
Divide 25 by 2 to get 12 as the quotient and 1 as the remainder.
Divide 12 by 2 to get 6 as the quotient and 0 as the remainder.
Divide 6 by 2 to get 3 as the quotient and 0 as the remainder.
Divide 3 by 2 to get 1 as the quotient and 1 as the remainder.
Divide 1 by 2 to get 0 as the quotient and 1 as the remainder.
Now write the remainders from bottom to top to get 1100100 (binary of 100).
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.