Lesson 4 of 8 · Grades 3 to 5
Capacity and volume
Capacity measures how much a container can hold. The metric system uses millilitres and litres, and customary units use cups, pints, quarts and gallons. This lesson shows how the units fit together.
How much a container holds
Capacity is the amount a container can hold. Volume is the amount of space the liquid or the object takes up. A jug has a capacity of 1 litre, and the juice inside it has a volume of 750 millilitres. In the kitchen and at school, the two words are used almost the same way, and both are measured with the same units.
The metric units for capacity are the millilitre (mL) and the litre (L). One litre is 1,000 millilitres. A teaspoon holds about 5 mL, a can of drink about 350 mL, a bottle about 1 L, and a bucket about 10 L. The jug below is marked every 250 mL and holds 750 mL of water, which is three quarters of a litre.
Cups, pints, quarts and gallons
Customary capacity has a chain of units. A cup is the smallest of them in everyday use, and one cup is 8 fluid ounces. Two cups make one pint, two pints make one quart, and four quarts make one gallon. That means one gallon is sixteen cups. Recipes use cups, milk comes in pints or quarts, and larger containers are sold by the gallon.
Choosing a unit
Choose the unit that keeps the number manageable. Millilitres suit small amounts such as a spoonful of medicine or a splash of milk in a cup. Litres suit bottles, jugs and buckets. Cups and pints suit recipes, and gallons suit large containers such as a fish tank or a fuel tank. A drink bottle of 500 mL and a drink bottle of 0.5 L hold exactly the same amount, so both answers are correct.
A litre is a little more than a quart. That is why a 1 L bottle and a 1 qt bottle look almost the same size, with the litre bottle holding slightly more. For everyday comparisons, treat them as close enough, but keep the exact facts for arithmetic inside each system.
Millilitres and litres together
A capacity in two units is a sum, just like length and mass. A jug holding 2 L 400 mL holds 2,000 mL + 400 mL = 2,400 mL. Going the other way, 1,500 mL is 1 L 500 mL, because 1,000 mL make one litre and 500 mL is left over. A number line in litres shows where those amounts sit between the whole litres.
Watch out for this
Do not add millilitres to litres without changing one of them first. A recipe with 1 L of water and 250 mL of juice holds 1,250 mL in total, not 251 mL and not 1,250 L. Change everything to the smaller unit, add, then write the answer in the unit the question asks for.
Worked example
A punch bowl holds 3 L 700 mL. How many millilitres is that, and how many 250 mL cups can it fill?
Step 1: change the litres to millilitres. 1 L = 1,000 mL, so 3 L = 3,000 mL.
Step 2: add the millilitres. 3,000 mL + 700 mL = 3,700 mL.
Step 3: share the punch into cups. Each cup holds 250 mL, so divide 3,700 by 250.
Step 4: 3,700 ÷ 250 = 14 with 200 left over, so the bowl fills 14 cups and has 200 mL left.
Answer: 3,700 mL, which fills 14 cups with 200 mL left over.
Remember
- One litre is 1,000 millilitres.
- Two cups make a pint, two pints make a quart, four quarts make a gallon.
- Millilitres suit small amounts and litres suit bottles and buckets.
- Write both amounts in one unit before you add or subtract.
Try it
Answer the five questions below. Work them out first, then open each answer to check.
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How many millilitres are in one litre?
Show answer
1,000 millilitres. One litre is a thousand millilitres.
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How many cups are in one pint?
Show answer
2 cups. One pint is two cups.
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A bottle holds 2 L. How many millilitres is that?
Show answer
2,000 millilitres. 2 × 1,000 = 2,000 mL.
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How many pints are in one quart?
Show answer
2 pints. One quart is two pints.
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A jug holds 1 L 250 mL. How many millilitres is that?
Show answer
1,250 millilitres. 1,000 + 250 = 1,250 mL.
Puzzle · Jug marks
Puzzle time
A jug has 800 mL of juice. Ava pours in another 350 mL. At which mark does the juice level stop?
Show a hint
Add the poured amount to the amount already in the jug: 800 + 350.
Show the answer
Answer: 1,150 mL. 800 + 350 = 1,150, so the juice level stops at the 1,150 mL mark.