What is Subitizing?

I used perceptual subitizing to "know" that there were three green hair curlers here.

Suzanne at Guided Math Study Group emailed me about subitizing the other day.

Alas, I had never heard this term. So I did some research and thought I’d share what I’d learned.

Subitizing is a way of instantly counting. In fancy math terms it would be getting to the cardinal number of a set (how many) without without going through the ordinals (counting each one’s position).

There are two types, perceptual and conceptual. Perceptual is perceiving the number of objects immediately. Conceptual is putting a little effort into it.

For instance, I glanced at the hot rollers Daughter had scattered on my side of the bed. I perceived there were three on the nightstand. But I had to do a little conceptual subitizing to arrive at the number of curlers on the floor (see the pictures).

I had to mentally "chunk" these hair curlers into smaller perceivable bundles to conceptually subitize the number here.

Here is a list of resources I found about it:

In the next article, I’ll attempt to answer the two questions I see associated with subitizing:

  • If you do it, how did you learn to do it?
  • How do we teach children to do it?

What do you think of these questions? Do you do it? Do you teach it?

(By the way, it is pronounced with ooo – like “Ooo! Subitizing is neat!”)

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