Perimeter
Sum of all side lengths of a shape. Year 3/4 starts simple; Year 5/6 finds missing sides.
Perimeter is the distance around a shape. Sum the side lengths. Year 5 introduces compound shapes where some side lengths must be deduced from given dimensions.
Worked examples
Rectangle 5cm × 3cm: perimeter = 5+3+5+3 = 16cm.
Square side 4cm: perimeter = 4×4 = 16cm.
L-shape: split visible sides; for missing internal sides, deduct from the opposite outer side.
Frequently asked questions
Same units throughout?
Yes — convert mm to cm or m before summing. KS2 SATs occasionally test this conversion.
Perimeter or circumference?
Perimeter is the general term. Circumference is the specific name for the perimeter of a circle (Year 6/KS3).