How Homeschoolers Do It (Archives Series): A Measuring Lesson

First posted 2010.

The book: Math Mammoth Light Blue Grade 3B, unit on measurement, lesson on "Milliliters and Liters."

The props: 250 ml measuring cup, 1 liter measuring cup, 1.2 ml measure (also known as a quarter teaspoon), several bottles and packages from the cupboard, several cups and mugs, water, towel.

Purpose of the lesson: to introduce the idea of volume, using the metric system. We have done linear measurement, first in imperial and then in metric units; we've weighed things, first in imperial and then in metric units; and now we're onto volume. I'm deliberately switching the order this time, since although we use lots of teaspoons and cups in cooking here (I cannot wrap my brain around cooking without my teaspoons and tablespoons), we don't hear as much about pints, quarts and gallons. So today's lesson focused on metric volume.

What we did: I put several bottles, jars and packages from the cupboard and fridge on the table, and asked Crayons to sort them into the ones that were marked g or kg (labelled by weight) and the ones that were marked ml or L (labelled by volume). The cereal and baking soda went to one side; the vanilla extract and juice went to the other. What was the difference? Crayons figured out quickly that the dry foods were mostly sold by weight, and the liquids were sold by volume. (Honey is an exception--I still don't know why it's sold by weight instead of volume.)

I showed Crayons how much a liter is (as big as our big measuring cup), and how much a milliliter is (about as small as the quarter-teaspoon measure which also shows 1.2 ml).

Then I had her do an activity from the worksheet: measuring the volume of cups, glasses, jars, or other small containers. We poured water into the cups and then poured it back into measuring containers. The Apprentice's giant tea cup holds 500 ml (2 cups for you Americans); an average coffee mug holds 300 ml; a small drinking glass holds 200 ml; and a tiny doll cup holds 5 ml. (We had to measure that one with a spoon.)

We skipped several of the calculating activities on the sheet--I'll probably have her go back over some of them tomorrow. Instead, we skipped to the end of the lesson, where there were three word problems. "One shampoo bottle contains 1 liter of shampoo. Another one contains 478 ml. How much more does the bigger one contain?" The other two problems were about drink bottles and juice in a pitcher.

And after all that we were very thirsty.

I told Crayons that if she wants a homework assignment, she should go ask The Apprentice if she can examine her stash of cosmetics, lotions, potions etc. and see which ones are packaged by weight and which are packaged by volume. I just thought of another fun homework assignment: figuring out how much toothpaste and shampoo you can fit in a zipper bag to get through airport security without going over the milliliter limit. See, grownups have to know about this stuff too.