Computer Science

Multiplying binary numbers

Long multiplication with binary numbers is very similar to the practice you will have learned for long multiplication of denary numbers.

Let's consider multiplying the number 1010 by 101.

First we multiply the top number by the first digit in the second number.

Then we put in a 0 and multiply our number by the second digit in the second number.

Then we put in two 0s and multiply our number by the third digit in the second number.

Finally we add together the three rows of binary numbers using the rules we learned about binary addition.

Checking these numbers against denary we can see that 10 x 5 is indeed 50.

Binary multiplication practice

Feedback: Answer a question and receive feedback on your answer

Generate a sum, do the multiplication and check your answer below. Use the extra row (blue) to show your carries when adding the numbers.