CC.4 Convert and compare metric units of volume
What is volume?
Volume is the amount of space that a solid figure takes up. We measure volume in cubic units. When we measure the volume of a liquid, we often use metric units such as liters and milliliters.
- A small juice box holds about 200 milliliters of juice.
- A large water bottle holds 1 liter of water.
- A bathtub can hold about 150 liters of water.
Volume is different from length or weight. It tells us how much space something fills or how much liquid it can hold.
Metric units of volume
The metric system uses liters (L) and milliliters (mL) to measure volume. A liter is the base unit. A milliliter is a very small unit. The prefix milli- means one thousandth, so 1 liter equals 1,000 milliliters.
- 1 liter = 1,000 milliliters
- 1 milliliter = 0.001 liter
- A teaspoon holds about 5 milliliters.
- A soda can holds about 355 milliliters.
Always check the unit label. Writing “5” without “mL” or “L” does not tell you the volume.
Converting liters to milliliters
To convert from a larger unit to a smaller unit, you multiply. Since 1 liter equals 1,000 milliliters, multiply the number of liters by 1,000 to find the number of milliliters.
- 2 L = 2 × 1,000 = 2,000 mL
- 5 L = 5 × 1,000 = 5,000 mL
- 0.5 L = 0.5 × 1,000 = 500 mL
- 3.2 L = 3.2 × 1,000 = 3,200 mL
When you multiply by 1,000, the number becomes larger. This makes sense because milliliters are smaller than liters, so you need more of them.
Converting milliliters to liters
To convert from a smaller unit to a larger unit, you divide. Since 1,000 milliliters equals 1 liter, divide the number of milliliters by 1,000 to find the number of liters.
- 3,000 mL = 3,000 ÷ 1,000 = 3 L
- 7,500 mL = 7,500 ÷ 1,000 = 7.5 L
- 250 mL = 250 ÷ 1,000 = 0.25 L
- 12,000 mL = 12,000 ÷ 1,000 = 12 L
Dividing by 1,000 moves the decimal point three places to the left. For example, 7,500 ÷ 1,000 = 7.5.
Using multiplication and division to convert
You can use a simple rule to remember how to convert between liters and milliliters. Large to small: multiply. Small to large: divide. Always multiply or divide by 1,000.
- 4 L to mL: 4 × 1,000 = 4,000 mL
- 9,000 mL to L: 9,000 ÷ 1,000 = 9 L
- 1.5 L to mL: 1.5 × 1,000 = 1,500 mL
- 600 mL to L: 600 ÷ 1,000 = 0.6 L
When you convert, the amount of liquid does not change. Only the unit changes. For example, 2 liters and 2,000 milliliters are the same amount.
Comparing metric units of volume
To compare two volumes, they must be in the same unit. If they are in different units, convert one or both amounts first. Then compare the numbers using the symbols > (greater than), < (less than), or = (equal to).
- 2 L ? 1,500 mL → 2,000 mL > 1,500 mL, so 2 L > 1,500 mL
- 3,000 mL ? 3 L → 3,000 mL = 3 L, so 3,000 mL = 3 L
- 500 mL ? 1 L → 500 mL < 1,000 mL, so 500 mL < 1 L
- 4.5 L ? 4,200 mL → 4,500 mL > 4,200 mL, so 4.5 L > 4,200 mL
Never compare a number in liters with a number in milliliters without converting. For example, 1 L is not less than 900 mL; 1 L equals 1,000 mL, which is greater than 900 mL.
Solving word problems with metric volume
When you solve a word problem, first find the volumes and their units. Then convert if needed. Finally, compare, add, or subtract to answer the question.
- Maya has a 2-liter bottle of water. She pours out 750 milliliters. How much water is left? 2 L = 2,000 mL. 2,000 − 750 = 1,250 mL, or 1.25 L.
- A recipe needs 1.5 liters of milk. Ben has 1,200 milliliters. Does he have enough? 1.5 L = 1,500 mL. 1,200 mL < 1,500 mL, so he does not have enough.
- Three bottles hold 500 mL, 750 mL, and 1 L. What is the total volume? 500 + 750 + 1,000 = 2,250 mL, or 2.25 L.
Always write the unit in your answer. If the problem uses liters, you may give the answer in liters. If it uses milliliters, you may give the answer in milliliters.
Estimating reasonable volumes
Estimating helps you check if an answer makes sense. Use everyday objects to help you estimate. A small spoon holds about 5 milliliters. A large pitcher holds about 2 liters.
- A medicine dropper holds about 1 milliliter.
- A small milk carton holds about 250 milliliters.
- A kitchen sink holds about 20 liters.
- A swimming pool holds thousands of liters.
If an answer seems too large or too small, check your conversion. For example, 5 liters is about 5,000 milliliters, not 500 milliliters.
Using decimal numbers with metric volume
Metric units work well with decimals. You can write 1.5 liters or 1,500 milliliters. Both mean the same amount. When you convert, keep the decimal point in the correct place.
- 0.75 L = 750 mL
- 2.25 L = 2,250 mL
- 0.2 L = 200 mL
- 3.6 L = 3,600 mL
When you multiply a decimal by 1,000, move the decimal point three places to the right. For example, 0.75 × 1,000 = 750.
Metric volume and place value
The metric system is based on powers of ten. This connects to place value. Moving from liters to milliliters is like moving three places to the right on a place value chart. Moving from milliliters to liters is like moving three places to the left.
- 1 L = 1,000 mL (three places right)
- 1,000 mL = 1 L (three places left)
- 4 L = 4,000 mL
- 4,000 mL = 4 L
Understanding place value helps you convert quickly. The digits stay the same; only the decimal point moves.
Checking your work
After you convert or compare, check your answer. Ask yourself: Does the unit match the question? Is the number reasonable? You can also convert back to the original unit to see if you get the same amount.
- Convert 3 L to mL: 3 × 1,000 = 3,000 mL. Check: 3,000 ÷ 1,000 = 3 L.
- Compare 2,500 mL and 2.5 L: 2,500 mL = 2.5 L. They are equal.
- Convert 800 mL to L: 800 ÷ 1,000 = 0.8 L. Check: 0.8 × 1,000 = 800 mL.
Checking your work helps you catch mistakes. It also builds confidence in your math skills.
Why metric volume matters
Metric units of volume are used all over the world. They are used in science, cooking, medicine, and everyday life. Knowing how to convert and compare them helps you understand information and solve real problems.
- A doctor may measure medicine in milliliters.
- A scientist may measure liquid in liters.
- A cook may follow a recipe that uses milliliters or liters.
- A store may sell drinks in 1-liter or 2-liter bottles.
The more you practice converting and comparing metric volumes, the easier it becomes. Use the rules and examples in this study section to help you.
Common Core alignment: CCSS.MATH.CONTENT.4.MD.A.1 – Know relative sizes of measurement units within one system of units including km, m, cm; kg, g; lb, oz; L, mL. Within a single system of measurement, express measurements in a larger unit in terms of a smaller unit. Record measurement equivalents in a two-column table.
Notes for teachers
This resource is designed to provide clear explanations, examples, and practice for learners of different needs and levels of support. It may be used for whole-class instruction, guided practice, independent learning, review, homework, or additional reinforcement at home.