Computers seem clever, but underneath they are built from billions of tiny switches that can only be on or off. That is why computers use binary: a counting system with just two digits, 0 and 1. Understanding it, even a little, helps children see that computers are not magic. They are fast and patient, and they follow simple rules.
Counting with two digits
We normally use ten digits (0 to 9), probably because we have ten fingers. When we run out of digits, we add a new column. After 9 comes 10: one "ten" and zero "ones."
Binary works the same way, but we run out of digits much sooner. The columns are worth 1, 2, 4, 8, 16 and so on, each double the last.
1is 110is one 2 and no 1, so 211is 2 + 1, so 3100is one 4, so 4101is 4 + 1, so 5
Each column is either on (1) or off (0). To read a binary number, add up the values of the columns that are on.
The finger trick
Hold up your right hand. Let each finger stand for a value, from the thumb: 1, 2, 4, 8, 16. A finger that is up counts; a finger that is down does not.
- Thumb up only: 1
- Index finger up only: 2
- Thumb and index up: 1 + 2 = 3
- Middle finger up only: 4
- Thumb, index and middle up: 1 + 2 + 4 = 7
With five fingers, you can count from 0 up to 31. Challenge your child to show their age, or the date of their birthday, using only their fingers.
Converting a number
To turn 13 into binary, ask which column values add up to 13:
- 8 fits, leaving 5.
- 4 fits, leaving 1.
- 2 does not fit.
- 1 fits.
So the columns 8, 4 and 1 are on, which gives 1101.
A secret code activity
Letters can be turned into numbers (A = 1, B = 2, and so on) and then into binary. For example, the letter C is 3, which is 00011 in five columns.
- Pick a short word like
CAB. - Convert each letter to its number: 3, 1, 2.
- Write each in five-column binary:
00011 00001 00010. - Hand it to a friend with the key and let them decode it.
(Real computers use a longer standard code for letters, but the principle is the same.)
Why it matters
Everything on a computer, whether a picture, a song or a video, is stored as long runs of 0s and 1s. A pixel's colour is a number. A letter is a number. That helps children grasp that data is just information in a form a machine can handle. It also connects to how the web works, where all that data travels as numbers.
Keep it playful
You do not need to be a maths expert, and mastery of binary is not necessary for learning to code. Treat it as a fun puzzle and a peek behind the curtain. If your child enjoys it, the Thinking course has more activities that explore how computers work.