As Piseth my friends just walk in to IT Subject, He ask me how to convert from Decimal to Binary or Binary to Decimal. I’ve left it for long time ago, So I might be forget how to do it. Hope this article will help you or me to do it again.

The decimal (base ten) numeral system has ten possible values (0,1,2,3,4,5,6,7,8, or 9) for each place-value. In contrast, the binary (base two) numeral system has two possible values, often represented as 0 or 1, for each place-value.

To avoid confusion while using different numeral systems, the base of each individual number may be specified by writing it as a subscript of the number. For example, the decimal number 156 may be written as 156₁₀ and read as “one hundred fifty-six, base ten”. The binary number 10011100 may be specified as “base two” by writing it as 10011100₂.

Since the binary system is the internal language of electronic computers, serious computer programmers should understand how to convert from decimal to binary. Although, converting in the opposite direction, from binary to decimal, is often easier to learn first.

Choose a method of conversion

• Comparison with descending powers of two and subtraction
• Short division by two with remainder

Comparison with descending powers of two and subtraction

1. List the powers of two in a “base 2 table” from right to left. Start at 2⁰, evaluating it as “1″. Increment the exponent by one for each power. The list, to ten elements, would look like this: 512, 256, 128, 64, 32, 16, 8, 4, 2, 1
2. For this example, let’s convert the decimal number 156₁₀ to binary. What is the greatest power of two that will fit into 156? Since 128 fits, write a 1 for the leftmost binary digit, and subtract 128 from your decimal number, 156. You now have 28.
3. Move to the next lower power of two. Can 64 fit into 28? No, so write a 0 for the next binary digit to the right.
4. Can 32 fit into 28? No, so write a 0.
5. Can 16 fit into 28? Yes, so write a 1, and subtract 16 from 28. You now have 12.
6. Can 8 fit into 12? Yes, so write a 1, and subtract 8 from 12. You now have 4.
7. Can 4 (power of two) fit into 4 (working decimal)? Yes, so write a 1, and subtract 4 from 4. You have 0.
8. Can 2 fit into 0? No, so write a 0.
9. Can 1 fit into 0? No, so write a 0.
10. Since there are no more powers of two in the list, you are done. You should have 10011100. This is the binary equivalent of the decimal number 156. Or, written with base subscripts: 156₁₀ = 10011100₂

Here is the example of this method written on a piece of paper. The steps are labeled “A” through “L”.

Repetition of this method will result in memorization of the powers of two, which will allow you to skip step 1.

Short division by two with remainder

This method is much easier to understand when visualized on paper. It relies only on division by two.

1. For this example, let’s convert the decimal number 156₁₀ to binary. Write the decimal number as the dividend inside an upside-down “long division” symbol. Write the base of the destination system (in our case, “2″ for binary) as the divisor outside the curve of the division symbol.2)156
2. Write the integer answer (quotient) under the long division symbol, and write the reminader (0 or 1) to the right of the dividend.2)156 0
   78
3. Continue downwards, dividing each new quotient by two and writing the remainders to the right of each dividend. Stop when the quotient is 1.2)156 0
   2)78 0
   2)39 1
   2)19 1
   2)9 1
   2)4 0
   2)2 0
   1
4. Starting with the bottom 1, read the sequence of 1’s and 0’s upwards to the top. You should have 10011100. This is the binary equivalent of the decimal number 156. Or, written with base subscripts: 156₁₀ = 10011100₂

The binary (base two) numeral system has two possible values, often represented as 0 or 1, for each place-value. In contrast, the decimal (base ten) numeral system has ten possible values (0,1,2,3,4,5,6,7,8, or 9) for each place-value.

To avoid confusion while using different numeral systems, the base of each individual number may be specified by writing it as a subscript of the number. For example, the binary number 10011100 may be specified as “base two” by writing it as 10011100₂. The decimal number 156 may be written as 156₁₀ and read as “one hundred fifty-six, base ten”.

Since the binary system is the internal language of electronic computers, serious computer programmers should understand how to convert from binary to decimal. Converting in the opposite direction, from decimal to binary, is often more difficult to learn first.

Note: This is ONLY for counting and does not talk about ASCII translations.

1. For this example, let’s convert the binary number 10011011₂ to decimal. List the powers of two from right to left. Start at 2⁰, evaluating it as “1″. Increment the exponent by one for each power. Stop when the amount of elements in the list is equal to the amount of digits in the binary number. The example number, 10011011, has eight digits, so the list, to eight elements, would look like this: 128, 64, 32, 16, 8, 4, 2, 1
2. Write the binary number below the list.
   

   Here is this step written on paper using the example binary number, 10011011.
3. Draw lines, starting from the right, connecting each consecutive digit of the binary number to the power of two that is next in the list above it. Begin by drawing a line from the first digit of the binary number to the first power of two in the list above it. Then, draw a line from the second digit of the binary number to the second power of two in the list. Continue connecting each digit with its corresponding power of two.
   

   Here is this step written on paper using the example binary number, 10011011.
4. Move through each digit of the binary number. If the digit is a 1, write its corresponding power of two below the line, under the digit. If the digit is a 0, write a 0 below the line, under the digit.
   

   Here is this step written on paper using the example binary number, 10011011.
5. Add the numbers written below the line. The sum should be 155. This is the decimal equivalent of the binary number 10011011. Or, written with base subscripts: 10011011₂ = 155₁₀
   

   Here is this step written on paper using the example binary number, 10011011. The sum of the bottom row, 155, is its decimal equivalent. Or, written with base subscripts: 10011011₂ = 155₁₀
6. Repetition of this method will result in memorization of the powers of two, which will allow you to skip step 1.

Doubling Method:

Starting from zero, and working from left to right, double your number and add the next digit of the base two representation. For example to convert 1011001, we take the following steps.

1. 1|011001 0*2+1 = 1
2. 10|11001 1*2+0 = 2
3. 101|1001 2*2+1 = 5
4. 1011|001 5*2+1 = 11
5. 10110|01 11*2+0 = 22
6. 101100|1 22*2+0 = 44
7. 1011001 44*2+1 = 89