There are no "standard" sizing charts for baby's or children's footwear, at least in the US.
It seems that every company has their own and lengths can vary up to 1 inch per size.
You wouldn't believe how many hours I have spent researching this. I have collected about 100 charts. Some are close, but most vary quite a bit.
Out of necessity, I too have created my own size chart.
This chart will help you with my bootie patterns and for any custom baby booties you have me make for you.
Even though I included an "Approximate Age" column, you as well as I know, babies are not born the same weight and length, with the same size feet. They also grow at different rates.
The most accurate way to determine what size you need is by measuring and comparing the length of your baby's or child's feet to the finished length of the bootie and allow for wiggle room and growth.
Both of these measurements are included on this chart.
All of my bootie patterns follow this chart, except the Airplane Bootie has it's own...for now.
Clicking on the chart should take you to a larger picture. If it does not and you'd like the full page version of it, or if you have any questions, please contact me.