Helpfully, if you've a printer, you can download free cut-out shoe size gauges like this one from Start-Rite (just be sure for accuracy the document's set up to print at 100% size). Alternatively, take careful foot length and width measurements (see 'how to' below), then refer to the site you’re buying from to see if it has its own size guide online. If not, convert your measurements using the standard sizing guide below.
https://www.startriteshoes.com/paper-measuring-gaugeHow to measure children's feet
1. Get them to stand up straight (assuming they can), wearing the type of socks/tights they’ll wear with their shoes. Use a tape measure or ruler to take the distance from back of heel to tip of their longest toe. Repeat for the other foot and record the longest of the two measurements - it's normal for kids, and grown-ups for that matter, to have two slightly different-sized feet.
2. Check the conversion chart below to see what shoe size your measurement relates to, rounding up if it falls between sizes. It’s wise to add about 1.5cm extra space for wriggle room and growth. If you think they're growing especially fast, consider choosing one half-size bigger than you need.
3. If your child needs a width other than the industry standard 'F' (which fits the majority of children), choose 'D-E' for narrow, 'G' for wide or 'H' for extra-wide feet. This doesn’t need measuring each time – once wide-footed you’re generally always wide-footed, so go with the width of previous shoes they've been measured for.
Source: MSE Money Tips