Area is the squares inside a shape. Perimeter is the distance round its edge. Count them first, then find the quick ways.
Tap each square to count it.
Area
The space inside a shape, counted in squares (cm²).
Perimeter
The distance all the way round the edge (cm).
Area of a rectangle
Rows × squares in each row
length × width
Perimeter of a rectangle
Add all four sides
length + width + length + width
Area is the space inside a shape, counted in squares, so it is measured in square units like cm². Perimeter is the distance all the way round the edge, so it is measured in units of length like cm.
Multiply the length by the width. A rectangle 5 cm long and 3 cm wide has 3 rows of 5 squares, so its area is 5 × 3 = 15 cm². Counting the squares first shows why this works.
Cut it into two rectangles, find the area of each one, then add them. It doesn't matter which way you cut: the total is always the same.
Children count squares for area and measure round shapes at about 7 or 8. The area of rectangles by multiplying, L-shapes, and the same area with different perimeters come at about 9 to 11.