Liquid Volume and Mass

Grade 3 · Math · Study Guide

Learn how to measure liquid volume in liters and mass in grams and kilograms.

Two important kinds of measurement in Grade 3 are liquid volume (how much liquid something holds) and mass (how heavy something is). Both use the metric system.

Liquid volume is measured in liters (L) and milliliters (mL). A liter is about the size of a large water bottle. 1 liter = 1,000 milliliters. A teaspoon holds about 5 mL, while a bathtub holds about 300 liters! When you add or subtract volumes, you work with these units just like regular numbers.

Mass is how much matter is in an object — not quite the same as weight, but close enough for our purposes. Mass is measured in grams (g) and kilograms (kg). A paperclip is about 1 gram. A textbook is about 1 kilogram. 1 kilogram = 1,000 grams. Estimating mass is a useful skill: a feather is about 1 g, a shoe is about 500 g, and you might weigh about 30 kg!

In word problems, you often need to add masses or volumes together, or compare them. Watch the units — always make sure you are adding grams to grams or liters to liters, not mixing them up.

Estimating Measurements
Object	Measurement	Unit
Teaspoon of water	5 mL	milliliters
Juice box	250 mL	milliliters
Large water bottle	1 L	liters
Paperclip	1 g	grams
Apple	200 g	grams
Your backpack	2-4 kg	kilograms

Key terms

Liter (L): The standard metric unit for measuring liquid volume.
Milliliter (mL): A smaller unit of liquid volume. 1,000 mL = 1 L.
Gram (g): The standard metric unit for measuring mass. A paperclip is about 1 gram.
Kilogram (kg): A larger unit of mass. 1 kg = 1,000 grams. A textbook is about 1 kg.
Mass: The amount of matter in an object, measured in grams or kilograms.

Flashcards

Liter (L): Metric unit of liquid volume. A big water bottle holds about 1 liter.
Milliliter (mL): Tiny liquid unit. 1,000 mL = 1 L.
Gram (g): Small mass unit. A paperclip is about 1 gram.
Kilogram (kg): Larger mass unit. 1 kg = 1,000 g. A textbook weighs about 1 kg.
Add volumes: Add liter values just like regular numbers. 5 L + 3 L = 8 L.
Add masses: Add gram or kilogram values. 500 g + 300 g = 800 g.

Practice questions

A fish tank holds 25 liters of water. Another holds 18 liters. How many liters total?
1. 33
2. 43
3. 47
4. 45
Show answer
Answer: 43
25 + 18 = 43 liters total.
A bag of rice has a mass of 3 kg. A bag of flour has a mass of 2 kg. What is the total mass?
1. 1 kg
2. 5 kg
3. 6 kg
4. 4 kg
Show answer
Answer: 5 kg
3 kg + 2 kg = 5 kg total mass.
1 kilogram is equal to 1,000 grams.
Show answer
Answer: True
The metric conversion: 1 kilogram = 1,000 grams.
A large water bottle holds about 1 ___.
Show answer
Answer: liter
Standard large water bottles hold about 1 liter (1,000 mL).
A puppy has a mass of 4 kg. A cat has a mass of 5 kg. How much more mass does the cat have?
1. 1 kg
2. 2 kg
3. 9 kg
4. 3 kg
Show answer
Answer: 1 kg
5 kg − 4 kg = 1 kg more mass for the cat.

Fun facts

The word "liter" comes from an old French unit called the "litron." France helped create the metric system in the 1790s to make measurement fair and consistent worldwide.
Your brain weighs about 1.4 kilograms — that's heavier than a can of soup but lighter than a bag of flour!

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