Perimeter: grid squares and polygons

In this lesson, we will learn:

• Perimeter is the straight-line measurement of the total distance to trace around a shape
• The perimeter of a polygon can be found by adding the lengths of all sides together
• The perimeter of a figure made of grid squares is found by tracing around the outside edges only
• The formula shortcuts for the perimeter of rectangular figures made of grid squares

Notes:

• Perimeter is the measurement around the outside of a two-dimensional shape
• For a polygon (shape with straight sides only), the perimeter can be calculated by adding all the sides in the shape together

• Grid squares are building blocks of figures and measure 1cm on all sides.
• To find the perimeter of a shape made of grid squares, count each edge around the OUTSIDE of the shape only.

• If grid squares make a rectangular figure (4-sided polygon with 2 pairs of matching sides), then a short cut can be used for finding the perimeter:
• Perimeter =2 × length + (2 × width)
• OR Perimeter =2 × (length + width)