Area of a circle

The Maths Habit

The pink square is as wide as the radius. About how many pink squares would cover the circle?

radius

Just over 3. Four squares make the big square, and the circle is a bit less.

Round to 1 decimal place.

8.368.4
42.7142.7
125.68125.7

Centre
The middle point of a circle.
Radius
From the centre to the edge.
Diameter
All the way across, through the centre.
Area
The space inside a shape.

Work out the area to 1 decimal place.

5 cmradius
1Find the radius.
r=5cm
2Press the keys.
π×5×5=
78.53981634
3Round to 1 decimal place.
A=78.5cm²

Work out the area to 1 decimal place.

8 cmradius
1Find the radius.
r=8cm
2Press the keys.
π×8×8=
201.0619298
3Round to 1 decimal place.
A=201.1cm²

Work out the area to 1 decimal place.

5 cmradius
1Find the radius.
r=5cm
2Press the keys.
π×5×5=
78.53981634
3Round to 1 decimal place.
A=78.5cm²
1radius2π×radius×radius=31 decimal place

Work out the area to 1 decimal place.

20 cmradius
1Find the radius.
r=20cm
2Press the keys.
π×20×20=
1256.637061
3Round to 1 decimal place.
A=1256.6cm²

Work out the area to 1 decimal place.

5 cmradius
1Find the radius.
r=5cm
2Press the keys.
π×5×5=
78.53981634
3Round to 1 decimal place.
A=78.5cm²
1radius2π×radius×radius=31 decimal place

Work out the area to 1 decimal place.

25 mradius
1Find the radius.
r=25m
2Press the keys.
π×25×25=
1963.495408
3Round to 1 decimal place.
A=1963.5m²

Work out the area to 1 decimal place.

5 cmradius
1Find the radius.
r=5cm
2Press the keys.
π×5×5=
78.53981634
3Round to 1 decimal place.
A=78.5cm²
1radius2π×radius×radius=31 decimal place

Work out the area to 1 decimal place.

21 cmradius
1Find the radius.
r=21cm
2Press the keys.
π×21×21=
1385.44236
3Round to 1 decimal place.
A=1385.4cm²

Is the pink line a radius or a diameter?

ADiameter
BRadius
CDiameter

Work out the area to 1 decimal place.

24 cmdiameter
1Find the radius.
r=24÷ 2 =12cm
2Press the keys.
π×12×12=
452.3893421
3Round to 1 decimal place.
A=452.4cm²

Work out the area to 1 decimal place.

22 cmdiameter
1Find the radius.
r=22÷ 2 =11cm
2Press the keys.
π×11×11=
380.1327111
3Round to 1 decimal place.
A=380.1cm²

Work out the area to 1 decimal place.

24 cmdiameter
1Find the radius.
r=24÷ 2 =12cm
2Press the keys.
π×12×12=
452.3893421
3Round to 1 decimal place.
A=452.4cm²
1r =diameter÷ 22π×radius×radius=31 decimal place

Work out the area to 1 decimal place.

28 mdiameter
1Find the radius.
r=28÷ 2 =14m
2Press the keys.
π×14×14=
615.7521601
3Round to 1 decimal place.
A=615.8m²

Work out the area to 1 decimal place.

24 cmdiameter
1Find the radius.
r=24÷ 2 =12cm
2Press the keys.
π×12×12=
452.3893421
3Round to 1 decimal place.
A=452.4cm²
1r =diameter÷ 22π×radius×radius=31 decimal place

Work out the area to 1 decimal place.

26 mmdiameter
1Find the radius.
r=26÷ 2 =13mm
2Press the keys.
π×13×13=
530.9291585
3Round to 1 decimal place.
A=530.9mm²

Work out the area to 1 decimal place.

24 cmdiameter
1Find the radius.
r=24÷ 2 =12cm
2Press the keys.
π×12×12=
452.3893421
3Round to 1 decimal place.
A=452.4cm²
1r =diameter÷ 22π×radius×radius=31 decimal place

Work out the area to 1 decimal place.

32 cmdiameter
1Find the radius.
r=32÷ 2 =16cm
2Press the keys.
π×16×16=
804.2477193
3Round to 1 decimal place.
A=804.2cm²

Is it right?
Thumbs up: right. Thumbs down: wrong.

  1. Radius 4 cm. Area 50.3 cm².

    Right

  2. Diameter 10 cm. Radius 5 cm.

    Right

  3. Radius 5 cm. Area 31.4 cm².

    Wrong: 78.5 cm²

  4. Diameter 6 cm. Area 113.1 cm².

    Wrong: 28.3 cm²

Area of a circle worksheet, page 1

Area of a circle worksheet, page 2

Answer sheet

  1. A quarter of a circle has a radius of 10 cm. Work out its area to 1 decimal place.

    78.5 cm²

  2. A circle has an area of 78.5 cm². Work out its radius to the nearest whole number.

    5 cm

  3. Which is more pizza: one pizza 30 cm across, or two pizzas each 20 cm across?

    One 30 cm pizza

  1. Work out the area.

    907.9 cm2
    34 cmdiameter1Find the radius.r=34÷ 2 =17cm2Press the keys.π××=3Round to 1 decimal place.A=cm²

  2. Work out the area.

    1134.1 cm2
    19 cmradius1Find the radius.r=cm2Press the keys.π××=3Round to 1 decimal place.A=cm²

  3. A circle has a radius of 18 m. Work out its area to 1 decimal place.

    1017.9 m2
Exit tickets to print