I realize that I don't do this with my kids. I use my hand and arm to measure my kids feet, chest (for shirts) and waist. So I hold the armpit area of Noah's shirt with my right hand - between my thumb and index finger. Then I pull the other armpit with my left hand and hold it against my outstretched right arm. Noah's shirt measurement is from my thumb to the line on the back of my elbow. Isabella's would be the same plus 2 inches. This works for Isabella's waist as well.
For Noah's waist - which is still too small to reach the back of my elbow, I fold his pants in the middle and measure the halfway point on my hand. His folded pants would start at my wristline to the middle of my middle finger.
Noah's shoe fits right between my wristline and the line at the back of my elbow.
Don't you think my hand measurements are just as good as those giraffe height charts at the pediatrician's office? :)
I store these measurements on my phone so I can buy the kids clothes and shoes that fit perfectly even when they're not with me (This is most useful on out-of-the-country business trips for pasalubong shopping). Of course, I have to update the measurements every couple of months. But it sure beats having to bring out a tape measure (which isn't so easy to roll back into place) or paper-feet when measuring clothes at the mall.