Circumference of a circle

The Maths Habit

Which is longer: the way around the tin, or how tall it is?

aroundaround,unrolled

The way around. It is just over 3 times the width.

Round to 1 decimal place.

4.374.4
15.7215.7
31.8631.9

Centre
The middle point of a circle.
Radius
From the centre to the edge.
Diameter
All the way across, through the centre.
Circumference
The distance around the outside.

dcircumference, unrolled:ddda bit
The circumference is just over 3 diameters.
The exact number is π = 3.14159…
d=10cm
π×10=31.41592654
C=31.4cm
  1. 1Find the diameter.The dashed line, all the way across.
  2. 2Press the keys.π, then ×, then the diameter, then =.
  3. 3Round to 1 decimal place.Keep one digit after the point.

Work out the circumference to 1 decimal place.

5 cmdiameter
1Find the diameter.
d=5cm
2Press the keys.
π×5=
15.70796327
3Round to 1 decimal place.
C=15.7cm

Work out the circumference to 1 decimal place.

3 cmdiameter
1Find the diameter.
d=3cm
2Press the keys.
π×3=
9.424777961
3Round to 1 decimal place.
C=9.4cm

Work out the circumference to 1 decimal place.

5 cmdiameter
1Find the diameter.
d=5cm
2Press the keys.
π×5=
15.70796327
3Round to 1 decimal place.
C=15.7cm
1diameter2π×diameter=31 decimal place

Work out the circumference to 1 decimal place.

9 cmdiameter
1Find the diameter.
d=9cm
2Press the keys.
π×9=
28.27433388
3Round to 1 decimal place.
C=28.3cm

Work out the circumference to 1 decimal place.

5 cmdiameter
1Find the diameter.
d=5cm
2Press the keys.
π×5=
15.70796327
3Round to 1 decimal place.
C=15.7cm
1diameter2π×diameter=31 decimal place

Work out the circumference to 1 decimal place.

15 mdiameter
1Find the diameter.
d=15m
2Press the keys.
π×15=
47.1238898
3Round to 1 decimal place.
C=47.1m

Work out the circumference to 1 decimal place.

5 cmdiameter
1Find the diameter.
d=5cm
2Press the keys.
π×5=
15.70796327
3Round to 1 decimal place.
C=15.7cm
1diameter2π×diameter=31 decimal place

Work out the circumference to 1 decimal place.

13 cmdiameter
1Find the diameter.
d=13cm
2Press the keys.
π×13=
40.8407045
3Round to 1 decimal place.
C=40.8cm

1diameter2π×diameter=31 decimal place

Work out each circumference to 1 decimal place.

1
2 cmdiameter
d=2cm
π×2=
6.283185307
C=6.3cm
2
25 mmdiameter
d=25mm
π×25=
78.53981634
C=78.5mm
3
17 mdiameter
d=17m
π×17=
53.40707511
C=53.4m

Is the pink line a radius or a diameter?

ARadius
BDiameter
CRadius

5 cmradius5 cmradius
Two radii make a diameter.
d=5× 2 =10cm
π×10=31.41592654
C=31.4cm
  1. 1Find the diameter.Given the radius? Double it.
  2. 2Press the keys.π, then ×, then the diameter, then =.
  3. 3Round to 1 decimal place.Keep one digit after the point.

Work out the circumference to 1 decimal place.

3 cmradius
1Find the diameter.
d=3× 2 =6cm
2Press the keys.
π×6=
18.84955592
3Round to 1 decimal place.
C=18.8cm

Work out the circumference to 1 decimal place.

11 cmradius
1Find the diameter.
d=11× 2 =22cm
2Press the keys.
π×22=
69.11503838
3Round to 1 decimal place.
C=69.1cm

Work out the circumference to 1 decimal place.

3 cmradius
1Find the diameter.
d=3× 2 =6cm
2Press the keys.
π×6=
18.84955592
3Round to 1 decimal place.
C=18.8cm
1d =radius× 22π×diameter=31 decimal place

Work out the circumference to 1 decimal place.

8 cmradius
1Find the diameter.
d=8× 2 =16cm
2Press the keys.
π×16=
50.26548246
3Round to 1 decimal place.
C=50.3cm

Work out the circumference to 1 decimal place.

3 cmradius
1Find the diameter.
d=3× 2 =6cm
2Press the keys.
π×6=
18.84955592
3Round to 1 decimal place.
C=18.8cm
1d =radius× 22π×diameter=31 decimal place

Work out the circumference to 1 decimal place.

20 mradius
1Find the diameter.
d=20× 2 =40m
2Press the keys.
π×40=
125.6637061
3Round to 1 decimal place.
C=125.7m

Work out the circumference to 1 decimal place.

3 cmradius
1Find the diameter.
d=3× 2 =6cm
2Press the keys.
π×6=
18.84955592
3Round to 1 decimal place.
C=18.8cm
1d =radius× 22π×diameter=31 decimal place

Work out the circumference to 1 decimal place.

23 cmradius
1Find the diameter.
d=23× 2 =46cm
2Press the keys.
π×46=
144.5132621
3Round to 1 decimal place.
C=144.5cm

1d =radius× 22π×diameter=31 decimal place

Work out each circumference to 1 decimal place.

1
21 mradius
d=21× 2 =42m
π×42=
131.9468915
C=131.9m
2
22 mmradius
d=22× 2 =44mm
π×44=
138.2300768
C=138.2mm
3
16 cmradius
d=16× 2 =32cm
π×32=
100.5309649
C=100.5cm

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

  1. Diameter 8 cm. Circumference 25.1 cm.

    Right

  2. Radius 3 cm. Diameter 6 cm.

    Right

  3. Radius 5 cm. Circumference 15.7 cm.

    Wrong: 31.4 cm

  4. Diameter 6 cm. Circumference 18.9 cm.

    Wrong: 18.8 cm

Circumference of a circle worksheet, page 1

Circumference of a circle worksheet, page 2

Answer sheet

  1. A bike wheel has a diameter of 60 cm. How far does the bike go in 10 turns? Give your answer in metres to 1 decimal place.

    18.8 m

  2. A circle has a circumference of 31.4 cm. Work out its diameter to the nearest whole number.

    10 cm

  3. Without a calculator, estimate the circumference of a circle with a diameter of 20 cm.

    About 60 cm

  1. Work out the circumference.

    106.8 cm
    17 cmradius1Find the diameter.d=17× 2 =34cm2Press the keys.π×=3Round to 1 decimal place.C=cm

  2. Work out the circumference.

    97.4 cm
    31 cmdiameter1Find the diameter.d=cm2Press the keys.π×=3Round to 1 decimal place.C=cm

  3. A circle has a radius of 24 m. Work out its circumference to 1 decimal place.

    150.8 m
Exit tickets to print