I have a math-teacher confession. (Again.) It's not something I'm proud of. Not something I like to admit.
I'm not very good at estimating measurements.
Oh, I'm okay at the small stuff, particularly with length. I can say, "This is about two inches," or even, "That's about fifteen centimeters." But if you go much beyond something I can hold in my hands, I'm pretty hopeless.
This drove me nuts in driver's ed. Rules like, "When parking on the street, you must be X feet from the corner," were useless for me. Thirty feet, fifty feet, doesn't matter. I have no mental gauge for a distance like that.
Weights are even worse. Give me something and ask me if it's closer to five pounds or ten, and I'll be straight-up guessing. I know the fifty-pound bags of salt are pretty close to the limit of what I can comfortably lug around, so if something else is close to that, my guesstimate will be okay.
You know what this all has in common? Experience.
I can estimate lengths of things smaller than a breadbox because I've done a lot of measuring with a 12-inch ruler. I can tell when things are close to that fifty-pound mark because lugging those salt bags down to the basement is a memorable experience. I don't have a lot of experience measuring and knowing larger distances.
I bet if I played football, I'd have a pretty good feel for five yards vs. ten yards vs. twenty.
Except ... I have students who play football and don't know what a yard is.
As much as I'm not great with measurement, it's a much weaker area for many of my students. (Oh, if I could tell you how many times I've asked, "How many inches are in a foot?" or even, "How many months in a year?" and gotten blank stares!) Some of it's a language issue, and some is that it hasn't been prioritized in their previous years of math education. Mostly, it's a combination of both.
So, students in some of my math classes will be attacking objects with rulers and yardsticks and tape measures and scales. I will throw lots of questions at them like, "If you were measuring the water to fill up a bathtub, would you use gallons or cups?" And I will hope some of it sinks in.
What mad measurement skills do you have? What areas trip you up? Any tips or tricks? I'd love to hear 'em.