The Numerical Measurement Method
Easy to perform and accurate to a T, I recommend a flexible tape measure (like those used by sewers and knitters) to measure your baby's foot. Use a colored marker to note directly on the tape measure how long your baby's foot is and just toss it in your purse. It's easy to transport, won't get mashed in your purse, and will prove incredibly accurate when you go to the store to measure crib shoes.
For me, it was always a milestone when their teeny
toes met with the tip of my finger. While it may seem a silly measuring
method, it can actually prove pretty useful when you're buying crib
shoes; if you know how long your baby's foot is (when compared to your
index finger) it makes it easier to hold up a crib shoe and compare the
two.