Capacity

We can learn how much a container can hold by using the concept of capacity. Everything from the cups we use to drink from to the bathtubs we play in contains it. We shall explore the concept of capacity in this chapter, find out why it is important and see how it is measured.

What is Capacity?

Capacity is physical quantity to measure how much liquid or substance a container can hold. It quantifies the volume or space available within a container to store a particular substance, typically measured in units such as litres, gallons or millilitres. Think of it as the "amount of water" a glass can keep inside.

Look at these four glasses:

1. The first glass has less than half the water it can hold. The capacity of water is ¼ of the glass.
2. The second glass is about halfway full. The capacity of water is ½ of the glass.
3. The third glass is more halfway and less than full glass. The capacity of water is ¾ of the glass.
4. The last glass is filled to capacity with water. The capacity of water is equal to that of the glass.
5. We can also say that capacity is the maximum amount of liquid a container can hold without spilling out.

Another word we use for capacity is "volume". Volume means how much space is inside a closed container.

We measure capacity in litres, millilitres, centilitres and other metric units. So, when you see a number with "L" or "mL", it tells you how much the container can hold without overflowing. The non-metric units of capacity are gallons, quarts, pints, etc.

Capacity Measurement Units

The standard units to measure capacity are litres (L) and millilitres (mL). The relationship between litres and millilitres is given by:

1 litre = 1000 millilitres

Metric Units of capacity

Metric conversion of capacity typically involves converting between litres (L) and millilitres (mL) since these are commonly used units for measuring capacity or volume.

Conversion of Metric Units

When you want to change from a smaller unit to a bigger unit, you multiply the number associated with the smaller unit of capacity by 10.

When you want to change from a bigger unit to a smaller unit, you divide the number associated with the bigger unit of capacity by 10.

The conversion of one unit to another is shown as:

Here are the basic metric conversions for capacity:

Litres (L) to millilitres (mL):

→ 1 litre (L) = 1,000 millilitres (mL)

This means that if you have a volume or capacity measurement in litres and you want to convert it to millilitres, you can multiply the number of litres by 1000.

→ For example: 5 litres (L) = 5 × 1000 mL = 5,000 millilitres (mL).

Millilitres (mL) to Litres (L):

→ 1 millilitre (mL) = 1/1000 litres (L)

If you have a volume or capacity measurement in millilitres and you want to convert it to litres, you can divide the number of millilitres by 1000.

→ For example: 15000 millilitres (mL) = 15000/1000 L = 15 litres (L).

Non-Metric Units

The non-metric units of capacity are gallons, quarts, pints, etc.

Conversion of Non-Metric Units

Conversion of non-metric units used to measure capacity are:

→ 1 Gallon = 4 Quarts
→ 1 Gallon = 8 Pints which means 1 Quart = 2 Pints

Example 1: Fill in the blank:

5 × 4.2 gallons = __________ pints

a) 148 
b) 158
c) 168
d) 188

Answer: c) 168

Explanation: 5 × 4.2 gallons = 21 gallons 
                                            = (21 × 8) pints
                                             = 168 pints

Example 2: The 950 centilitres of juice in a jar is poured into a glass. What is the amount in decalitres of juice left in the jar if the juice in the jar is 550 decilitres?

a) 4.55 dL
b) 45.5 dL
c) 4.55 daL
d) 45.5 daL

Answer: d) 45.5 daL

Explanation: Total capacity of juice in the jar = 550 dL

Capacity of juice in the glass = 950 dL
                                           = 950/10
                                            = 95 dL

Amount of juice left in the jar = (550 − 95) dL 
                                            = 455 dL

Amount of juice left in the jar in decalitres = 455/100 daL
                                                              = 45.5 daL