Even if math isn’t your favorite subject, there’s a good chance you love pie for dessert or a pizza pie at a party. Pi Day, which falls on March 14th each year, is a perfect time to use tasty round foods to learn more about math. These Pi Day activities for kids can make the day fun for anyone!

### Why March 14th?

The shortest expression of Pi is the number 3.14. March is the third month of the year, so the 14th day of March became known as Pi Day, giving teachers everywhere yet another excuse to get excited about math. For mega-math-fan bonus points, kick off a Pi Day celebration at 1:59 p.m., to represent the next three digits of Pi.

### What is Pi, anyway?

Pi is an irrational number. This means it’s a decimal number that never ends or repeats. Like other irrational numbers, Pi also can’t be expressed as either a ratio or a fraction. So far, scientists have calculated Pi into ten trillion digits. What makes Pi interesting is that no matter what size circle you measure, it always appears as the same number. Try it and see for yourself!

### Calculating Pi

You need to know the parts of a circle to calculate Pi. The diameter of a circle is the length of a straight line passing through its center. The radius of a circle is a line extending from the center of a circle to the outer edge or circumference of the circle. Pi is the ratio of the circumference (outer edge) to its diameter (length across the center). To calculate Pi, divide the circumference of a circle by its diameter.

### Pi Day Vocabulary Words

**Mathematics** – The scientific study of numbers, quantities, measurements, and shapes

**Pi** – The ratio of the circumference of a circle to its diameter

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**Ratio** – The numeric relationship between two or more things

**Rational Number** – A number that can be written as a fraction of integers, which include natural numbers, negative numbers, zero, fractions, and decimals that either end or repeat

**Irrational Number** – A decimal number that can’t be written as a fraction and never ends or repeats

**Circle** – A curved line that meets, with every point on that line being the same distance from the center

**Diameter** – A straight line that passes through the center of a figure

**Radius** – A line extending from the center of a circle to the circumference

**Circumference** – The line that goes around a circle

**Measure** – To find out the size, weight, length, or amount of something

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### Math Activity: Pizza Pi

This activity teaches students some basic math facts, including measuring the diameter, radius, and circumference of a circle with the option to calculate Pi for students who can do division. Warning: May cause pizza cravings!

#### Materials you’ll need:

Cardboard circles pre-cut to 10”, 12”, and 14”

Poster board or white/ivory cardstock

Construction paper

Scissors

Glue

Crayons/markers

Yarn or string

Felt or other fabric scraps (optional)

- Using poster board or cardstock, trace a circle for pizzas using one of three pre-cut cardboard templates (small, medium, large).
- Cut out each circle to make the pizza “crust.”
- Have students make “toppings” using crayons/markers and scraps of paper and/or fabric.
- Sample toppings: Sauce, cheese, pepperoni, sausage, mushrooms, peppers, pineapple.
- When the pizzas are finished, have students measure each of their pizzas from one side to the other and write down that number. That is the diameter of their pizza.
- Ask students how they might determine where the center point is within their pizzas.
- Have students measure the radius of their pizzas (this is the distance from the center of a circle to the outer edge), and write that number down.
- Have students take their string and measure the circumference of their pizzas and write that number down.
- To calculate Pi, students can use the formula circumference divided by diameter. The number should be 3.14, or close to it.

### Math Activity: Finding Pi in Everyday Objects

Materials you’ll need:

A variety of round and/or cylindrical objects, like plates and paint cans

Yarn or string

Scissors

Tape

Paper

Pencils, Pens, or Crayons

- Take a piece of yarn or string and wrap it around the circumference of the round object.
- Cut the string to measure exactly around the circular object.
- Place the same length of string you just cut, stretch it across the diameter of the circle, and cut the string.
- Do this again until you run out of string.
- How many pieces do you have? (Students should have 3 pieces plus a smaller piece that would be around 1/7 of the diameter, or: Pi.)
- Repeat this experiment for at least one more circular object to see if the results repeat.

### Number Pie Math Game

While not a game that will explore irrational numbers, this is literally a PIE game! The rules are easy, and this math game helps students memorize single digit multiplication drills. Click on over for the full game with printable pie ‘fillings’ and instructions: