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Mass and Capacity: Grams, Kilograms, Millilitres and Litres

Tell mass from capacity, choose a sensible metric unit, estimate with everyday benchmarks and convert with the same 1000 pattern. Includes 28 original Grade 3–5 questions with explanations.

Grades 3–5 · 28 practice questions · Original material
Learning objectiveDecide whether a question is about mass or capacity, choose g, kg, mL or L, check an estimate against a benchmark, and convert mixed units such as 2 kg 50 g without losing the zero.

The idea

Mass tells how heavy something is. Capacity tells how much a container can hold. A big balloon has a large capacity but very little mass; a small rock has almost no capacity but quite a lot of mass. So before you choose a unit, ask: am I weighing it, or filling it?

Mass is measured in grams (g) and kilograms (kg). Capacity is measured in millilitres (mL) and litres (L). Both pairs follow the same pattern: 1 kg = 1000 g and 1 L = 1000 mL. To change kilograms to grams or litres to millilitres, multiply by 1000. To go back, divide by 1000.

Benchmarks help you check whether an answer is reasonable. A paper clip has a mass of about 1 g. A teaspoon holds about 5 mL. A Canadian pop can holds 355 mL, and a metric measuring cup holds 250 mL. The water in a full 1 L bottle has a mass of about 1 kg. That last benchmark is for water only; other liquids can be lighter or heavier for the same capacity.

Mixed units need care with zeros. 2 kg 50 g is 2000 g + 50 g = 2050 g, not 250 g and not 2500 g. Line up the thousands, hundreds, tens and ones before you add, just as you would with any four-digit number.

Worked examples

Mass and capacity benchmarks on two thousand-part scalesTop scale: 1 kilogram equals 1000 grams, with a paper clip at about 1 gram and a 500 gram block halfway. Bottom scale: 1 litre equals 1000 millilitres, with a teaspoon at 5 millilitres, a pop can at 355 millilitres and a measuring cup at 250 millilitres. Arrows show multiply by 1000 to change kilograms to grams or litres to millilitres, and divide by 1000 to go back.Two scales, the same 1000 patternMass: how heavy. Capacity: how much a container holds. Benchmarks are approximate.MASS0 g500 g1000 g = 1 kgpaper clip ≈ 1 g1 L of water ≈ 1 kgCAPACITY0 mL1000 mL = 1 Lteaspoon ≈ 5 mLcup 250 mLpop can 355 mLkg → g, L → mL: × 1000g → kg, mL → L: ÷ 1000
The same thousand-part pattern links grams to kilograms and millilitres to litres. Benchmarks are rounded everyday estimates; the scales are drawn to the labelled values, not to real object sizes.

Example 1 · Mass or capacity?

A pitcher is full of lemonade. Which unit would you use for (a) how much lemonade it holds, and (b) how heavy the full pitcher is?

  1. (a) 'How much it holds' is a filling question, so it is capacity. A pitcher holds more than a cup but far less than a bathtub, so litres fit.
  2. (b) 'How heavy' is a weighing question, so it is mass. A full pitcher is heavier than an apple, so kilograms fit.

(a) litres (capacity); (b) kilograms (mass).

Example 2 · Keep the zero

Write 4 kg 75 g in grams.

  1. 4 kg = 4 × 1000 g = 4000 g.
  2. 75 g has 0 hundreds, 7 tens and 5 ones.
  3. 4000 + 75 = 4075. The zero holds the hundreds place.

4 kg 75 g = 4075 g.

Example 3 · Millilitres to litres and millilitres

Write 2600 mL as litres and millilitres.

  1. Each 1000 mL makes 1 L. 2600 contains two full thousands.
  2. 2600 − 2000 = 600 mL left over.

2600 mL = 2 L 600 mL.

Example 4 · Compare in the same unit

Which is heavier: 1 kg 90 g or 1200 g?

  1. Change both to grams: 1 kg 90 g = 1000 + 90 = 1090 g.
  2. Compare 1090 g with 1200 g. 1200 is greater.

1200 g is heavier. Checking 1 kg 90 g as '1 kg 900 g' would be a place-value mistake.

Example 5 · Two steps with a check

A 2 L bottle of juice is shared into 250 mL cups. How many cups can be filled?

  1. Change to the same unit: 2 L = 2000 mL.
  2. 2000 ÷ 250 = 8.
  3. Check with the benchmark: four 250 mL cups make 1 L, so two litres make 8 cups.

8 cups.

Common mistakes

These are tempting because they use familiar operations. Check what the question is actually measuring.

Thinking a bigger object must be heavier.

Why this fails: Size and mass are different. A large box of tissue can have less mass than a small bag of sugar.

Writing 2 kg 50 g as 250 g or 2500 g.

Why this fails: 50 g has 0 hundreds. 2 kg 50 g = 2000 g + 50 g = 2050 g.

Multiplying when you should divide.

Why this fails: Grams are smaller units, so there are more of them. Going from kg to g, the number gets bigger (× 1000); going from g to kg, it gets smaller (÷ 1000).

Using litres for mass or grams for capacity.

Why this fails: Litres measure how much a container holds; grams measure how heavy something is.

Applying '1 L ≈ 1 kg' to every liquid.

Why this fails: The benchmark is for water. One litre of cooking oil, for example, has a mass a little less than 1 kg.

Foundation

Foundation practice

Mass or capacity? Choose the unit and use benchmarks.

Choose the unit

1. Which unit would you use for the mass of an apple?

  1. litres
  2. grams
  3. kilometres
  4. millilitres
Choose the unit

2. Which unit would you use for the amount of water a bathtub holds?

  1. grams
  2. millilitres
  3. litres
  4. kilograms
Choose the unit

3. Which unit would you use for the mass of a large bag of potatoes?

  1. kilograms
  2. grams
  3. litres
  4. centimetres
Mass or capacity

4. Is 'How much juice does this jug hold?' a mass question or a capacity question?

Benchmark

5. What is the best estimate for the mass of one paper clip?

  1. 1 kg
  2. 100 g
  3. 10 kg
  4. 1 g
Benchmark

6. What is the best estimate for the amount of medicine in one teaspoon?

  1. 5 mL
  2. 5 L
  3. 500 mL
  4. 50 L
Compare

7. Which holds more: a 355 mL can or a 1 L bottle?

Practice

Practice practice

Convert with the 1000 pattern, including mixed units.

Convert

8. 3 kg = ___ g

Convert

9. 4000 mL = ___ L

Mixed units

10. 2 kg 300 g = ___ g

Mixed units

11. 5 L 250 mL = ___ mL

Mixed units

12. 1500 g = ___ kg ___ g

Benchmark

13. How many 250 mL cups fill a 1 L jug?

Convert

14. Half a kilogram = ___ g

Think

Think practice

Spot the trap before you calculate.

Reason

15. Which has more mass: 1 kg of feathers or 1000 g of rocks?

  1. The rocks
  2. The feathers
  3. They have the same mass
  4. You cannot tell without knowing their size
Find the error

16. Sam writes: 2 kg 50 g = 250 g. What is wrong, and what is correct?

Order

17. Order from least to greatest: 1 kg 200 g, 1100 g, 1 kg 50 g.

  1. 1 kg 50 g, 1100 g, 1 kg 200 g
  2. 1100 g, 1 kg 50 g, 1 kg 200 g
  3. 1 kg 200 g, 1100 g, 1 kg 50 g
  4. 1 kg 50 g, 1 kg 200 g, 1100 g
Reason

18. Ava says, 'The big box must be heavier than the small box.' Is she right?

Choose

19. A recipe needs 750 mL of milk. Which amount is exactly enough?

  1. Half a litre
  2. One 355 mL can and one teaspoon
  3. Three 250 mL cups
  4. Seven teaspoons
Reason

20. Does 1 L of cooking oil have a mass of exactly 1 kg?

Compare

21. Which is greater: 3 L or 2900 mL?

Challenge

Challenge practice

Multi-step problems. Convert to one unit first, then check the answer is sensible.

Real-world

22. In Ontario, a 4 L bag of milk holds three smaller bags of equal size. About how many millilitres are in each small bag?

Two steps

23. Mia's backpack holds books (1 kg 750 g), lunch (600 g) and a full water bottle (500 g). What is the total mass in kilograms and grams?

Remainder

24. A 2 L jug of lemonade is poured into 300 mL cups. How many cups can be filled completely, and how much lemonade is left?

Two steps

25. A bag holds 2 kg of flour. One batch of muffins uses 350 g. After 4 batches, how much flour is left?

Benchmark

26. The water in a full 1 L bottle has a mass of about 1 kg. About how much mass does 355 mL of water have?

Estimate

27. Which is the most reasonable estimate for the mass of the milk in a full 4 L bag?

  1. About 4 g
  2. About 400 g
  3. About 40 kg
  4. About 4 kg
Share equally

28. A 5 kg bag of rice is shared equally into 4 containers. How much rice goes in each, in kilograms and grams?

Answer key

  1. 1. grams
    An apple is light enough that grams give a sensible number (a few hundred grams). Litres and millilitres measure capacity, not mass.
  2. 2. litres
    This is capacity, and a bathtub holds a lot. Millilitres would also be correct but would give a very large number.
  3. 3. kilograms
    A big bag of potatoes weighs several kilograms. Grams would give a number in the thousands.
  4. 4. Capacity
    'How much it holds' is about filling a container, so it is capacity.
  5. 5. 1 g
    A paper clip is the classic benchmark for about 1 gram.
  6. 6. 5 mL
    A teaspoon holds about 5 mL. 500 mL is two cups.
  7. 7. The 1 L bottle
    1 L = 1000 mL, and 1000 mL is more than 355 mL.
  8. 8. 3000 g
    3 × 1000 = 3000.
  9. 9. 4 L
    4000 ÷ 1000 = 4.
  10. 10. 2300 g
    2000 g + 300 g = 2300 g.
  11. 11. 5250 mL
    5000 mL + 250 mL = 5250 mL.
  12. 12. 1 kg 500 g
    1500 contains one full thousand (1 kg) with 500 g left.
  13. 13. 4
    1000 ÷ 250 = 4.
  14. 14. 500 g
    Half of 1000 g is 500 g.
  15. 15. They have the same mass
    1 kg and 1000 g are the same amount. The feathers take up much more space, but space is not mass.
  16. 16. 2 kg is 2000 g, so the answer is 2050 g.
    Sam treated the 2 as if it were 200. Keep the 0 in the hundreds place: 2000 + 50 = 2050.
  17. 17. 1 kg 50 g, 1100 g, 1 kg 200 g
    In grams: 1050, 1100, 1200.
  18. 18. Not necessarily.
    Size tells how much space a box takes, not its mass. A big box of foam packing can be lighter than a small box of books.
  19. 19. Three 250 mL cups
    3 × 250 = 750 mL. Half a litre is only 500 mL.
  20. 20. No. It is a little less than 1 kg.
    The '1 L of water is about 1 kg' benchmark is for water. Different liquids can have different masses for the same capacity.
  21. 21. 3 L
    3 L = 3000 mL, and 3000 > 2900.
  22. 22. About 1333 mL
    4000 ÷ 3 = 1333 with 1 left over, so each bag is about 1333 mL. That is why the small bags are labelled 1.33 L.
  23. 23. 2 kg 850 g
    1750 + 600 + 500 = 2850 g = 2 kg 850 g.
  24. 24. 6 cups, with 200 mL left
    2000 ÷ 300 = 6 remainder 200. A seventh cup cannot be filled.
  25. 25. 600 g
    4 × 350 = 1400 g used. 2000 − 1400 = 600 g left.
  26. 26. About 355 g
    1000 mL of water ≈ 1000 g, so each millilitre of water is about 1 g.
  27. 27. About 4 kg
    Milk is mostly water, and 4 L of water is about 4 kg. 40 kg would be heavier than many children.
  28. 28. 1 kg 250 g
    5000 ÷ 4 = 1250 g = 1 kg 250 g.

Related practice

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