Capacity: Are There Enough?

In kindergarten, "capacity" in this lesson does not mean how much a cup or jug can hold. It means whether one group of objects has enough members to give one to each object in another group. For example, if there is a plate for every child at a table, then there are enough plates. If one child has no plate, then there are not enough.

This idea helps children build number sense before they even start counting large numbers. Instead of counting each group and comparing the totals, they simply pair items one at a time and watch what happens.

The main tool for answering "are there enough?" is one to one matching. Children draw an imaginary (or real) line from each object in the first group to exactly one object in the second group. Three things can happen:

Every object in both groups gets a partner, so there are exactly enough. Some objects in the first group are left without a partner, so there are not enough. Some objects in the second group are left without a partner, so there is more than enough.

Look at the five bunnies and the four carrots below. Match each bunny to one carrot.

Four bunnies each get a carrot, but the fifth bunny is left with no partner. Since one bunny has nothing, there are not enough carrots for all the bunnies.

Now look at four kids and four cups.

Because every kid gets a cup and every cup gets a kid, with nobody left out, this group has exactly enough. If there had been a fifth kid with no cup, it would not be enough. If there had been a fifth cup with no kid, there would be more than enough.

Matching one to one is the building block for comparing groups without needing to count large numbers right away. Once children are comfortable spotting "enough," "not enough," and "more than enough," they are ready to describe those same groups using the language of fewer or more, and eventually to line up two full sets of numbers side by side in comparing two numbers.

Always draw one line from each object to only one partner object, never two lines from the same object. Check the group with no partner left over first, since that group tells you whether there are enough or not. Remember that matching does not require counting the whole group, it only requires pairing.

Related lessons

• Kindergarten