In Introducing the Royal Measurements, we looked at some common imperial units for measuring capacity. Capacity is a measure of the amount something can contain, for example, how much juice will fit in a bottle. Here are a list of imperial capacity measurement units in order from smallest to largest: pints (pt), quarts (qt) and gallons (gal).

Converting units

Converting units is an application of ratios. We start by writing the conversion equation and look at how we multiply or divide to find the value of a certain quantity. Make sure your familiar with applications of ratios, then you can look through the following conversion charts, so we can start moving between imperial and metric units.

Metric units to imperial units

$1$1 litre = $2.11338$2.11338 pints

$1$1 litre = $1.05669$1.05669 quarts

$1$1 litre = $0.264172$0.264172 gallons

Imperial units to metric units

$1$1 gallon = $3.78541178$3.78541178 litres

$1$1 quart = $0.946353$0.946353 litres

$1$1 pint = $0.473176$0.473176 litres

Hint

You may have noticed that there are a lot of decimals when converting metric to imperial, or vice versa. To make these conversions easier, just round them to $1$1 decimal place e.g. $1$1 pint$\approx$≈$0.5$0.5 litres.

Worked Examples

Question 1

Using the conversion $1$1 gallon $=$=$4.5$4.5 litres, change each of these capacities from gallons to litres:

$5$5 gallons

$10$10 gallons

$40$40 gallons

$16$16 gallons

Question 2

Using the approximate conversion $1$1 gallon $=$=$4.5$4.5 litres, change each of these capacities from litres to gallons.

Give your answers correct to two decimal places where necessary.

$10$10 litres

$50$50 litres

$100$100 litres

$25$25 litres

Question 3

A van has a petrol tank that holds $11$11 gallons of petrol. How many litres of petrol is that?

Use the approximation $1$1 gallon $=$=$4.5$4.5 litres.