Length units as decimals

The idea

As 1 cm = 10 mm and 1 m = 100 cm, a millimetre is 0.1 cm and a centimetre is 0.01 m, so lengths in mm or cm are written as decimals of a cm or m.

Millimetres and centimetres

We know that 1 cm = 10 mm.

How much of a centimetre is 1 mm?

• 1 cm
• One-tenth of a cm
• One-hundredth of a cm

Set the bar

The bar shows whole cm (or m), cut into small units. Set it to each amount and read it as a decimal.

Smaller units as decimals

Because 1 cm = 10 mm, 1 mm is one-tenth of a cm. Because 1 m = 100 cm, 1 cm is one-hundredth of a m.

As 1 cm = 10 mm and 1 m = 100 cm, a millimetre is 0.1 cm and a centimetre is 0.01 m. Lengths in mm or cm are written as decimals of a cm or m.

• Length | As a decimal
• 1 mm | 0.1 cm
• 5 mm | 0.5 cm
• 12 mm | 1.2 cm
• 1 cm | 0.01 m
• 15 cm | 0.15 m

Notes

1 mm = 0.1 cm and 1 cm = 0.01 m. A length in mm or cm is written as a decimal of a cm or a m.

Check yourself

How many cm is 8 mm?

Answer: 0.8 cm

8 mm = 8/10 cm = 0.8 cm.

7.3 cm is how many mm?

Answer: 73 mm

7.3 cm = 7 cm + 0.3 cm = 70 mm + 3 mm = 73 mm.

35 cm is how many m?

Answer: 0.35 m

35 cm = 35/100 m = 0.35 m.

Which is the same length as 12 cm?

• 0.12 m — correct. Yes! 12 hundredths of a metre.
• 1.2 m. 1.2 m is 120 cm.
• 0.012 m. 0.012 m is only 1.2 cm.