How do you know if your child is obese? What’s baby fat, and what’s a spare tire? Kids aren’t just little adults in the Body Mass Index (BMI) department–they get their own, CDC-approved scale. Learn how to use it.

For many things, kids have no business being compared against other kids–it starts all sorts of other comparisons that can be cruel and unusual punishment. But for BMI–weight divided by height squared, in kilograms and meters–it’s the way to know if your kid is overweight, obese, or underweight.

The CDC has a terrific page about this, including growth charts. Check it out. Is your kid is too high?