Measures

Measuring Length, Weight, and Capacity

Junior Infants · Senior Infants · 1st Class · 2nd Class

✓Compare and order objects by length, weight, and capacity using non-standard units.
✓Understand the need for standard units of measurement.
✓Measure and estimate length using standard units like the metre and centimetre.
✓Measure and estimate weight using standard units like the kilogram and gram.
✓Measure and estimate capacity using standard units like the litre and millilitre.

Key concepts

Length

Length tells us how long or short something is. We can measure how far it is from one end to the other. Non-standard units: Using everyday things like paper clips, pencils, or hand spans to measure length. Standard units: Using special tools like a ruler or a metre stick. We use units like the centimetre (cm) and the metre (m).

Weight

Weight tells us how heavy or light something is. We can feel how much 'pull' gravity has on an object. Non-standard units: Using things like blocks or marbles on a balance scale to see which is heavier. Standard units: Using special scales to measure. We use units like the gram (g) and the kilogram (kg).

Capacity

Capacity tells us how much a container can hold. It's about how much liquid or sand can fit inside. Non-standard units: Using small cups or spoons to fill a bigger container and count how many it takes. Standard units: Using special measuring jugs. We use units like the millilitre (mL) and the litre (L).

Comparing

Looking at two or more things and saying which is longer/shorter, heavier/lighter, or holds more/less.

Ordering

Putting things in a line from shortest to longest, lightest to heaviest, or least capacity to most capacity.

Standard Units

Units that everyone uses, so our measurements are always the same. This helps us share information accurately and understand each other's measurements.

Key facts to remember

1Length tells us how long or short something is.
2Weight tells us how heavy or light something is.
3Capacity tells us how much a container can hold.
4We use words like 'longer', 'shorter', 'heavier', 'lighter', 'holds more', and 'holds less' to compare.
5Non-standard units (like paper clips or small cups) help us understand measurement first.
6Standard units (like centimetres, metres, grams, kilograms, millilitres, litres) help everyone measure in the same way.
7A metre (m) is much longer than a centimetre (cm).
8A litre (L) holds much more than a millilitre (mL).

Worked examples

Example 1

Compare the length of a pencil, a crayon, and a glue stick using paper clips. Then order them from shortest to longest.

ILay the pencil down. Place paper clips end-to-end beside it without gaps or overlaps. Count how many paper clips long the pencil is (e.g., 8 paper clips).

IIDo the same for the crayon (e.g., 5 paper clips).

IIIDo the same for the glue stick (e.g., 7 paper clips).

IVCompare the numbers: 5 is the smallest, 8 is the largest. This tells us the crayon is the shortest and the pencil is the longest.

Answer

The order from shortest to longest is: Crayon (5 paper clips), Glue Stick (7 paper clips), Pencil (8 paper clips).

Make sure all the paper clips you use are the same size and are placed carefully end-to-end.

Example 2

Measure the length of your maths copybook to the nearest centimetre using a ruler.

IPlace the ruler along one side of the copybook, making sure the '0' mark on the ruler is exactly at the start of the copybook.

IILook at where the end of the copybook lines up with the numbers on the ruler.

IIIRead the number of centimetres at the end of the copybook, rounding to the nearest whole centimetre if needed.

Answer

The maths copybook is approximately 20 centimetres (cm) long.

Always start measuring from the '0' mark on your ruler, not the very end of the ruler itself.

Example 3

You have a small cup, a jug, and a bucket. Which holds the most water? Which holds the least? How can we be sure?

IFirst, make a guess about which container holds the most and which holds the least water.

IIFill the small cup with water. Pour the water from the cup into the jug. Count how many small cups it takes to fill the jug (e.g., 5 cups).

IIIFill the small cup with water again. Pour the water from the cup into the bucket. Count how many small cups it takes to fill the bucket (e.g., 20 cups).

IVCompare the number of cups: The small cup holds 1 cup (itself), the jug holds 5 cups, and the bucket holds 20 cups.

VTo be even more accurate, we can use a measuring jug with standard units like litres (L) and millilitres (mL) to get an exact amount that everyone understands.

Answer

The bucket holds the most water (20 small cups). The small cup holds the least water (1 small cup). The jug holds more than the cup but less than the bucket (5 small cups). Using a measuring jug with litres and millilitres gives us an exact measurement.

Always use the same small cup for counting to make a fair comparison of capacity.

Common mistakes

✗Not starting at the '0' mark when using a ruler or measuring tape.
✗Leaving gaps or overlapping when using non-standard units (like blocks or paper clips) to measure length.
✗Confusing the units, for example, saying something is '5 kilograms long' instead of '5 kilograms heavy'.
✗Not using the same non-standard unit consistently when comparing (e.g., using different sized cups for capacity).
✗Guessing without trying to estimate first, or not checking a guess with a measurement.

Exam tips

★Always look carefully at what you are asked to measure: length, weight, or capacity.
★First, make a good guess (estimate), then try to measure to check your guess.
★When using non-standard units, make sure they are all the same size and placed carefully.
★Remember the names of the standard units: cm and m for length, g and kg for weight, mL and L for capacity.

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