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Year 5 Maths Mass

Measure mass & choose appropriate units

20 practice questions 0 video lessons Theory + worked examples
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Theory

Mass is how heavy something is. It is measured in milligrams (mg), grams (g), kilograms (kg) and tonnes (t). This Year 5 maths page shows how to choose a unit, read a dial scale by working out what each mark is worth, and compare and order masses.

Mass tells you how heavy an object is. Capacity units (mL, L) and length units (cm, m) do not measure mass.

Milligrams for tiny masses (a grain of rice, a tablet); grams for small things (a pencil, an apple); kilograms for heavier things (a bag of flour, a person); tonnes for very heavy things (a car, a loaded truck).

\(1\text{ g} = 1000\text{ mg}\), \(1\text{ kg} = 1000\text{ g}\) and \(1\text{ t} = 1000\text{ kg}\).

To read a scale, find what each small mark is worth: the difference between two numbered marks divided by the number of spaces between them.

Dial scale to 500 g A kitchen dial scale marked from 0 to 500 grams, numbered every 100 g with a small mark every 20 g. The pointer is halfway between 300 and 400, at 350 g. 0100200300400500 grams
Each small mark is \(20\) g. The pointer is at \(350\) g.
Dial scale to 20 kg A dial scale marked from 0 to 20 kilograms, numbered every 5 kg with a small mark every 1 kg. The pointer is three marks past 10, at 13 kg. 05101520 kilograms
Each small mark is \(1\) kg. The pointer is at \(13\) kg.

Units of mass:

\[ 1\text{ kg} = 1000\text{ g} \]
1 kg =1000 g
\[ 1\text{ t} = 1000\text{ kg} \]
1 t =1000 kg
\[ 1\text{ g} = 1000\text{ mg} \]
1 g =1000 mg
\[ \text{small mark} = \dfrac{\text{gap between numbers}}{\text{spaces}} \]
small mark = gap ÷ spaces
Read the unit on the scale. A scale marked in kilograms gives kilograms, not grams.
Compare digit by digit. Line masses up by place value, starting at the thousands.

Reading a dial scale

  1. Read the unit on the scale.
  2. Work out what each small mark is worth.
  3. Start at the numbered mark before the pointer and count on the small marks.

Ordering masses

  1. Write all the masses in the same unit.
  2. Compare the thousands, then the hundreds, tens and ones.
Example 1 — Choose a unit
Choose the best unit.
(i) A paper clip
(ii) A dog
(iii) A bus
(iv) A grain of sand
Solution

(i) Grams
(ii) Kilograms
(iii) Tonnes
(iv) Milligrams

Example 2 — Read a scale
Use the first diagram. What does the scale show?
Solution
\(100 \div 5\)\(=\)\(20\text{ g each mark}\)
100÷5=20 g

The pointer is halfway between \(300\) and \(400\), so the mass is \(350\) g.

Example 3 — Read a kilogram scale
Use the second diagram. What is the mass?
Solution
\(5 \div 5\)\(=\)\(1\text{ kg each mark}\)
5÷5=1 kg

Three marks past \(10\): \(13\) kg.

Example 4 — Convert
Write in grams.
(i) \(3\) kg
(ii) \(2.5\) kg
Solution
\(3 \times 1000\)\(=\)\(3000\text{ g}\)
\(2.5 \times 1000\)\(=\)\(2500\text{ g}\)
2.5×1000=2500 g

(i) \(3000\) g
(ii) \(2500\) g

Example 5 — Order masses
Write \(1708\) g, \(1780\) g, \(1078\) g and \(1870\) g from lightest to heaviest.
Solution

\(1078\) g, \(1708\) g, \(1780\) g, \(1870\) g.

Example 6 — Difference
How much heavier is the heaviest of those bags than the lightest?
Solution
\(1870 - 1078\)\(=\)\(792\text{ g}\)
1870−1078=792 g

\(792\) g heavier.

Example 7 — Estimate
Which is the best estimate for the mass of a laptop: \(2\) g, \(2\) kg, \(200\) kg or \(2\) t?
Solution

About \(2\) kg.

Example 8 — Table
Three sacks of animal feed have masses of \(14\) kg, \(9\) kg and \(31\) kg.
(i) What is the total mass?
(ii) How much heavier is the heaviest than the lightest?
Solution
\(14 + 9 + 31\)\(=\)\(54\text{ kg}\)
\(31 - 9\)\(=\)\(22\text{ kg}\)
14+9+31=54 kg

(i) \(54\) kg
(ii) \(22\) kg

Common pitfalls

Counting marks as 1 each. Work out the value of each small mark first.
Ignoring the unit on the scale. A pointer on 3 of a kilogram scale means 3 kg, not 3 g.
Mixing mass with capacity. mL and L measure how much a container holds, not how heavy it is.
Ordering by the last digits. \(1078\) is lighter than \(1708\): compare the hundreds first.

Frequently asked questions

What units measure mass?

Milligrams, grams, kilograms and tonnes.

How many grams are in a kilogram?

\(1000\).

How many kilograms are in a tonne?

\(1000\).

How do I read a scale with unnumbered marks?

Divide the gap between two numbers by the number of spaces. From \(300\) to \(400\) with \(5\) spaces, each mark is \(20\) g.

What unit is best for a truck?

Tonnes.

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