The idea in brief. Cut the disc into thin sectors and arrange them in a row, one pointing up, one pointing down, and they interlock into a near-rectangle. Its bottom edge is half the rolled-out rim, pi times the radius. Its height is the radius. So the area is pi times r, times r. In the lesson. Never the diameter. Halve it first.
Lesson video, with the working
Area of a circle
3 min 03 s
The film teaches 2 questions in turn. Each question shows first; its working is written as the film explains it.
How do you work out area of a circle questions in P6?
This page is about finding the area of a circle from its radius or its diameter, using whichever value of pi the question tells you to take.
What your child learns here
This page is about finding the area of a circle from its radius or its diameter, using whichever value of pi the question tells you to take. It belongs to Area and Circumference of Circle in the Primary 6 Area and Volume strand, and it also covers the area of a semicircle and a quarter circle.
Find the area of a circle as pi times the radius times the radius, taking pi as 3.14 or 22/7 as instructed.
Halve a given diameter to get the radius before the area rule is used.
Find the area of a semicircle as half of the circle, and a quarter circle as one quarter of it.
Leave an answer in terms of pi when asked: a radius of 7 cm gives 49 pi square centimetres.
Work backwards from a known area to the radius, then to the diameter if that is what is wanted.
Does the answer make sense?
When your child finds a whole circle's area, it must be more than 3 times but less than 4 times the radius times itself, and in square units. When a radius or diameter is asked for instead, it is a plain length in cm or m.
How to practise these questions
Basic questions train halving the diameter to get the radius before using the area formula. Intermediate questions add semicircles and quarter circles, answers left in terms of π, and finding the radius from an area. Challenge questions go from an area back to a diameter, or compare areas when the radius doubles. When a circle's area stalls, read the written step-by-step solution together.
Questions parents ask
Is area of a circle in the Primary 6 syllabus? Yes. The MOE Primary 6 syllabus lists area and circumference of circle under Area and Volume, together with the area and perimeter of semicircles and quarter circles.
Should my child use 3.14 or 22/7 for pi? Use whichever value the question gives. Questions state it, for example 'Take pi = 3.14', or ask for the answer in terms of pi. 22/7 is handy when the radius is a multiple of 7, because the 7 cancels.
Why does the area formula use the radius twice? Cut a circle into thin slices and lay them side by side, and they form a shape close to a rectangle. One side is half the rim, which is pi times the radius, and the other side is one radius. The lesson notes on this page show it step by step.
