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Grade 3 (age 8-9)

grade 3 Capacity and Weight

Capacity is how much a container can hold, and mass is how heavy something is. The capacity of a milk carton or a water bottle is measured in liters (L) and milliliters (mL), and the mass of an apple or a watermelon in kilograms (kg) and grams (g). 1 L is 1000 mL and 1 kg is 1000 g, so in both cases one big unit equals 1000 small units. Change the mL to raise or lower the water in the beaker, and change the g to move the needle on the scale; beside each picture, the same amount is written in both the big and the small unit.

What Is Capacity?

🥛 How Much a Container Holds
①A milk carton holds 1000 mL, which is 1 L
②A paper cup holds about 200 mL
③Containers of different shapes are hard to compare just by looking, so we compare capacity in L and mL

Units of Capacity

1200 mL
💡 1 L = 1000 mL
①Split 1 L into 1000 equal parts and each part is 1 mL
②The beaker starts at 1200 mL, which is 1000 mL and 200 mL, so it can also be written 1 L 200 mL
③To change mL to L, group the mL in sets of 1000

Units of Mass

2500 g
⚖️ 1 kg = 1000 g
①1 kg is 1000 g
②The scale starts at 2500 g, which is 2000 g and 500 g, so it is 2 kg 500 g
③Light things like an apple are easy to describe in g, and heavy things like a watermelon in kg

Summary

Units of Capacity
1 L = 1000 mL
1 L is 1000 times 1 mL
Units of Mass
1 kg = 1000 g
1 kg is 1000 times 1 g
Changing Units
Big unit → small unit: × 1000
Small unit → big unit is ÷ 1000; thinking in groups of 1000 makes it easy
🎯 Summary
①Capacity is how much a container holds, measured in L and mL
②Mass is how heavy something is, measured in kg and g
③1 L = 1000 mL and 1 kg = 1000 g
④To change a big unit to a small one multiply by 1000; to go back, divide by 1000
⑤Pick the unit that fits the size of what you are measuring

Examples and Unit Test

Example 1
How many milliliters are in 2 L?
1
1 L = 1000 mL.
2
2 L is 2 groups of 1000 mL, so 2 × 1000 = 2000 mL.
▸ 2000 mL
To change L to mL, multiply by 1000.
Example 2
How many kilograms and grams is 2500 g?
1
1000 g make 1 kg, so see how many groups of 1000 g fit in 2500 g.
2
2500 g = 2000 g + 500 g, and 2000 g is 2 kg, so it is 2 kg 500 g.
▸ 2 kg 500 g
The number of 1000 g groups gives the kilograms, and what is left over gives the grams.
Unit Test
How many grams are in 1 kg?
①10 g
②100 g
③1000 g
④500 g
▸ ③ 1000 g
1
Split 1 kg into 1 g pieces and you get 1000 pieces.
2
So 1 kg = 1000 g, and the answer is ③.
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