Strategies for estimating area and perimeter with unit squares

In this lesson, we will learn:

• How to count areas with squares and/or triangles (unit squares and half unit squares)
• How to estimate areas of shapes on an area grid

Notes:

• Review: finding perimeter and area for rectangular figures

• How do you find the area of shapes that are not made of squares?
• If you cut a square diagonally, you will get a triangle (half a square is a triangle)

• If you cut 2 squares diagonally (2 cm²), you will get half the area (1 cm²)
• There are other variations of getting half of a square (1/2 cm² or 0.5 cm²)
• There will also be cases where you won't know the exact amount shaded in one square, but you can say whether it is more or less than half

• To estimate areas of a shape on a grid, we can get close to the actual area by:
• Counting all the whole unit squares (fully shaded in or covered by the shape)
• Counting all the half unit squares (most commonly the diagonal triangle)
• Rounding any squares shaded more than half up to $\approx$ 1 cm²
• Rounding any squares shaded less than half down to $\approx$ 0 cm²