Prime numbers chart

A prime numbers chart is a hundreds chart with the primes shaded: 2, 3, 5, 7, 11 and the rest of the 25 primes below 100. A prime has exactly two factors, 1 and itself; every other number above 1 is composite.

Free printable PDF, 4th grade to 5th grade.

One page, black and white, prints the same every time.

Tap the sheet to print it. The picture follows the options you pick.

What is on the sheet

1 2 3 4 5 6 7 8 9 10
11 12 13 14 15 16 17 18 19 20
21 22 23 24 25 26 27 28 29 30
31 32 33 34 35 36 37 38 39 40
41 42 43 44 45 46 47 48 49 50
51 52 53 54 55 56 57 58 59 60
61 62 63 64 65 66 67 68 69 70
71 72 73 74 75 76 77 78 79 80
81 82 83 84 85 86 87 88 89 90
91 92 93 94 95 96 97 98 99 100

Reading the chart

The 25 shaded cells are the primes. Every unshaded number above 1 is composite, and 1 is neither: it has only one factor, so it does not fit the definition. The shading shows two things at once. After 2, no even number is prime, so the shaded cells sit in the odd columns; and after 5, nothing ending in 5 is prime either, so the 5s column is empty from 15 down.

The primes thin out as the numbers grow, from eight below 20 to only three between 80 and 100, which is a pattern children notice on their own if the chart is on the wall long enough.

The sieve, with this chart

The classic way to find the primes is to cross out the multiples of each prime in turn on a hundreds chart, which is called the sieve of Eratosthenes. Print the plain hundreds chart, cross out every multiple of 2 except 2, then of 3, 5 and 7, and what survives is exactly the shaded set on this chart. Doing it once by hand makes the shaded chart make sense; keeping the shaded chart afterwards saves redoing it every time a factor question comes up.

Fourth grade introduces prime and composite numbers alongside factors and multiples; 5th grade uses primes for factor trees and simplifying fractions.

Common questions

Is 1 a prime number?
No. A prime has exactly two factors, and 1 has only one. The chart leaves 1 unshaded.
Why is 2 prime when it is even?
Its only factors are 1 and 2, which is the definition. It is the only even prime, since every other even number has 2 as an extra factor.

More charts like this

Practice sheets that go with it