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Last updated on August 19, 2025
173 in binary is written as 10101101 because the binary system uses only two digits, 0 and 1, to represent numbers. This number system is used widely in computer systems. In this topic, we are going to learn about converting the number 173 to the binary system.
The process of converting 173 from decimal to binary involves dividing the number 173 by 2. Here, it is divided by 2 because the binary number system uses only 2 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 173 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 173 by 2 until getting 0 as the quotient is 10101101. 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 10101101. 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 10101101 in binary is indeed 173 in the decimal number system.
173 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 173 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 27 = 128 Since 128 is less than 173, we start from 27 = 128.
Step 2 - Identify the largest power of 2: In the previous step, we started at 27 = 128. 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, 173. Since 27 is the number we are looking for, write 1 in the 27 place. Now the value of 27, which is 128, is subtracted from 173. 173 - 128 = 45.
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, 45. So, the next largest power of 2 is 25 = 32, which is less than or equal to 45. Now, we have to write 1 in the 25 place. And then subtract 32 from 45. 45 - 32 = 13.
Step 4 - Continue identifying the largest powers of 2: Now, we continue with 13. The largest power of 2 that fits into 13 is 2^3 = 8. Write 1 in the 2^3 place. Subtract 8 from 13. 13 - 8 = 5.
Step 5 - Continue identifying the largest powers of 2: Now, we have 5. The largest power of 2 that fits into 5 is 2^2 = 4. Write 1 in the 2^2 place. Subtract 4 from 5. 5 - 4 = 1.
Step 6 - Continue identifying the largest powers of 2: Now, we have 1. The largest power of 2 that fits into 1 is 2^0 = 1. Write 1 in the 2^0 place. Subtract 1 from 1. 1 - 1 = 0.
Step 7 - Identify the unused place values: In steps 2-6, we wrote 1 in the 2^7, 2^5, 2^3, 2^2, and 2^0 places. Now, we can just write 0s in the remaining places, which are 2^6, 2^4, and 2^1. Now, by substituting the values, we get: 0 in the 2^6 place 0 in the 2^4 place 0 in the 2^1 place
Step 8 - Write the values in reverse order: We now write the numbers upside down to represent 173 in binary. Therefore, 10101101 is 173 in binary.
Grouping Method: In this method, we divide the number 173 by 2. Let us see the step-by-step conversion.
Step 1 - Divide the given number 173 by 2. 173 / 2 = 86. Here, 86 is the quotient and 1 is the remainder.
Step 2 - Divide the previous quotient (86) by 2. 86 / 2 = 43. Here, the quotient is 43 and the remainder is 0.
Step 3 - Repeat the previous step. 43 / 2 = 21. Now, the quotient is 21, and 1 is the remainder.
Step 4 - Repeat the previous step. 21 / 2 = 10. Here, the quotient is 10 and the remainder is 1.
Step 5 - Repeat the previous step. 10 / 2 = 5. Here, 5 is the quotient and 0 is the remainder. Step 6 - Repeat the previous step. 5 / 2 = 2. Here, 2 is the quotient and 1 is the remainder.
Step 7 - Repeat the previous step. 2 / 2 = 1. Here, 1 is the quotient and 0 is the remainder.
Step 8 - Repeat the previous step. 1 / 2 = 0. Here, the remainder is 1. And we stop the division here because the quotient is 0.
Step 9 - Write down the remainders from bottom to top. Therefore, 173 (decimal) = 10101101 (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 173. Since the answer is 2^7, write 1 next to this power of 2. Subtract the value (128) from 173. So, 173 - 128 = 45. Find the largest power of 2 less than or equal to 45. The answer is 2^5. So, write 1 next to this power. Now, 45 - 32 = 13. Find the largest power of 2 less than or equal to 13. The answer is 2^3. So, write 1 next to this power. Now, 13 - 8 = 5. Find the largest power of 2 less than or equal to 5. The answer is 2^2. So, write 1 next to this power. Now, 5 - 4 = 1. Find the largest power of 2 less than or equal to 1. The answer is 2^0. So, write 1 next to this power. Now, 1 - 1 = 0. Final conversion will be 10101101.
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, 173 is divided by 2 to get 86 as the quotient and 1 as the remainder. Now, 86 is divided by 2. Here, we will get 43 as the quotient and 0 as the remainder. Dividing 43 by 2, we get 21 as the quotient and 1 as the remainder. Dividing 21 by 2, we get 10 as the quotient and 1 as the remainder. Dividing 10 by 2, we get 5 as the quotient and 0 as the remainder. Dividing 5 by 2, we get 2 as the quotient and 1 as the remainder. Dividing 2 by 2, we get 1 as the quotient and 0 as the remainder. Dividing 1 by 2, we get 0 as the quotient and 1 as the remainder. We stop the division once the quotient becomes 0. Now, we write the remainders upside down to get the binary equivalent of 173, 10101101.
This rule also involves breaking the number into powers of 2. Identify the powers of 2 and write it down in decreasing order i.e., 2^7, 2^6, 2^5, 2^4, 2^3, 2^2, 2^1, and 2^0. Find the largest power that fits into 173. 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 173, we use 0s for 2^6, 2^4, and 2^1, and 1s for 2^7, 2^5, 2^3, 2^2, and 2^0.
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 173.
Memorize to speed up conversions: We can memorize the binary forms for numbers 1 to 173. Recognize the patterns: There is a peculiar pattern when converting numbers from decimal to binary. 1 → 1 1 + 1 = 2 → 10 2 + 2 = 4 → 100 4 + 4 = 8 → 1000 8 + 8 = 16 → 10000 16 + 16 = 32 → 100000 32 + 32 = 64 → 1000000 64 + 64 = 128 → 10000000...and so on. This is also called the double and add rule.
Even and odd rule: Whenever a number is even, its binary form will end in 0. For example, 8 is even and its binary form is 1000. Here, the binary of 8 ends in 0. If the number is odd, then its binary equivalent will end in 1. For example, the binary of 17 (an odd number) is 10001. As you can see, the last digit here is 1.
Cross-verify the answers: Once the conversion is done, we can cross-verify the answers by converting the number back to the decimal form. This will eliminate any unforeseen errors in conversion.
Practice by using tables: Writing the decimal numbers and their binary equivalents on a table will help us remember the conversions.
Here, let us take a look at some of the most commonly made mistakes while converting numbers to binary.
Convert 173 from decimal to binary using the place value method.
10101101
2^7 is the largest power of 2, which is less than or equal to 173. So place 1 next to 27. Subtracting 128 from 173, we get 45. The next largest power would be 25. So place another 1 next to 25. Now, subtracting 32 from 45, we get 13. The next largest power is 23. Place 1 next to 23. Subtracting 8 from 13 gives us 5. The next largest power is 22. Place 1 next to 22. Subtracting 4 from 5 gives us 1. The next largest power is 2^0. Place 1 next to 20. Now, subtracting 1 from 1 gives us 0. Now, we just place 0s in the remaining powers of 2, which are 26, 24, and 21. By using this method, we can find the binary form of 173.
Convert 173 from decimal to binary using the division by 2 method.
10101101
Divide 173 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 173 to binary using the representation method.
10101101
Break the number 173 into powers of 2 and find the largest powers of 2. We get 2^7. So 1 is placed next to 2^7. Next, 173 - 128 = 45. Now, the largest power of 2 is 2^5. Once again, 1 is placed next to 2^5. Now, 45 - 32 = 13. The largest power is 2^3. Place 1 next to 2^3. 13 - 8 = 5. The largest power now is 2^2. Place 1 next to 2^2. Subtract 4 from 5 to get 1. The largest power is now 2^0. Place 1 next to 2^0. Subtracting 1 from 1 gives us 0. After getting 0, fill in with zeros for unused powers of 2. By following this method, we get the binary value of 173 as 10101101.
How is 173 written in decimal, octal, and binary form?
Decimal form - 173 Octal - 255 Binary - 10101101
The decimal system is also called the base 10 system. In this system, 173 is written as 173 only. We have already seen how 173 is written as 10101101 in binary. So, let us focus on the octal system, which is base 8. To convert 173 to octal, we need to divide 173 by 8. So 173 / 8 = 21 with 5 as the remainder. In the next step, divide the quotient from the previous step (21) by 8. So 21 / 8 = 2 with 5 as the remainder. In the next step, divide the quotient from the previous step (2) by 8. So 2 / 8 = 0 with 2 as the remainder. The division process stops here because the quotient is now 0. Here, 5, 5, and 2 are the remainders, and they have to be written in reverse order. So, 255 is the octal equivalent of 173.
Express 173 - 68 in binary.
110101
173 - 68 = 105 So, we need to write 105 in binary. Start by dividing 105 by 2. We get 52 as the quotient and 1 as the remainder. Next, divide 52 by 2. Now we get 26 as the quotient and 0 as the remainder. Divide 26 by 2 to 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 0 as the quotient and 1 as the remainder. Now write the remainders from bottom to top to get 110101 (binary of 105).
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.