Kid-Friendly Perimeter Reference Chart
The Perimeter Power Guide
Everything You Need to Know About Measuring Edges!
What We Know
What is Perimeter?
Imagine you are an ant walking all the way around the very edge of a shape. The total distance you walk is the Perimeter! It’s like the length of a fence around a yard.
The Golden Rule:
To find the perimeter, you have to ADD UP EVERY SINGLE SIDE! Don't leave any side out, or the "fence" will have a hole in it.
Shape Secrets:
- Rectangles: These shapes have "twins." The top side is the same length as the bottom. The left side is the same length as the right.
- Wacky Shapes: Even if a shape looks strange (irregular), the rule is the same: just add up all the straight edges!
How We Show It
Mission 1: Finding the Total Perimeter
A shape has sides that are 5 inches, 3 inches, 2 inches, and 4 inches.
- Step 1: List all the numbers: 5, 3, 2, and 4.
- Step 2: Add them up! 5 + 3 + 2 + 4.
- Step 3: Solve it. 5+3 is 8, plus 2 is 10, plus 4 is 14.
- Step 4: Don't forget the label: 14 inches.
Mission 2: Finding a Missing Side
A rectangle has a perimeter of 20 inches. The top is 6 inches. How long are the sides?
- Step 1: Find the "twin." If the top is 6, the bottom is 6 too! (6 + 6 = 12).
- Step 2: Subtract from the total. 20 - 12 = 8 inches left over.
- Step 3: Split the leftover in half for the two sides. 8 ÷ 2 = 4.
- Step 4: Check your work! 6 + 6 + 4 + 4 = 20. Your missing side is 4 inches.
Watch Out! (Don't Get Tricked!)
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The Multiplication Trick:
Sometimes you might want to multiply (Length × Width). STOP! That's for Area (the grass inside). For Perimeter (the fence), you ALWAYS ADD.
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The "Invisible" Sides:
If a rectangle only has two numbers written on it, don't just add those two! Remember the "twins" and label every side before you start adding.
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The Square Unit Trap:
Don't write "square inches" for perimeter. It’s just regular "inches." It's a straight line, not a box!
Keep practicing, Perimeter Pro! • NC.3.MD.8 • Text Only Version
