How to Convert Decimal to Hexadecimal by Hand
By Mickael Gomes · Last updated: 2026-06-19
To convert a decimal number to hexadecimal by hand, divide the number by sixteen, write down the remainder, then keep dividing the quotient by sixteen until it reaches zero. Reading the remainders from the last one to the first gives the hexadecimal value. Any remainder from ten to fifteen is written as a letter A through F. The method is short, mechanical, and works for any whole number.
The repeated-division method
Pick the number you want to convert and divide it by sixteen. Record the whole-number quotient and the remainder separately. Then divide that quotient by sixteen again, recording the new quotient and remainder. Repeat until the quotient is zero. Each division produces one hexadecimal digit, and the digits emerge in reverse order, so the first remainder you find is the rightmost (least significant) hex digit.
The key habit is to convert remainders of ten through fifteen into letters as you go: ten becomes A, eleven B, twelve C, thirteen D, fourteen E, and fifteen F. Forgetting this step is the most common mistake people make.
Worked example: 700 in hex
Start with 700. Dividing 700 by 16 gives a quotient of 43 with a remainder of 12, and twelve is the letter C. Now divide 43 by 16: the quotient is 2 with a remainder of 11, which is the letter B. Finally divide 2 by 16: the quotient is 0 with a remainder of 2. The quotient has reached zero, so we stop.
Collect the remainders from last to first: 2, then B, then C. The answer is 2BC. You can confirm it by expanding: 2 times 256 is 512, B (eleven) times 16 is 176, and C (twelve) times 1 is 12. Adding 512 plus 176 plus 12 gives exactly 700.
A shortcut for small numbers
For any number from 0 to 255 you can skip the long division by splitting the value into two hex digits directly. Divide the number by sixteen once: the quotient is the first hex digit and the remainder is the second. For 200, 200 divided by 16 is 12 remainder 8, so the high digit is C and the low digit is 8, giving C8. This works because two hex digits exactly cover the range of a single byte.
Checking your answer
To verify any conversion, expand the hex value back to decimal by multiplying each digit by its place value (1, 16, 256, and so on) and adding the results. If the total matches your starting number, the conversion is correct. Doing this check once or twice builds confidence, and it is exactly the arithmetic an automatic converter performs for you when you would rather not divide by hand.