Speedo is a swimwear brand and it's also the name synonymous with brief-style swimwear worn by men or boys. Competitive swimmers prefer Speedo-style swimwear because it is designed to adhere to the body and allows for movement. Yet Speedo swimwear is suitable for everyday pool play as well. When fitting a boy for Speedo swimwear, you'll want to consider the size of his everyday clothing and use Speedo's fit guide.
Check the label on a pair of the boy's trousers to see what size they are. You're looking for a number between 6 and 20. This will give you an idea of what size Speedo he will wear.
Measure the boy's waist in inches.
Measure the boy's chest in inches.
Consult the Speedo size chart to select the size that best corresponds to the boy's measurements. Look under each even-numbered clothing size for the measurements that would fit the boy comfortably. For example, if he wears a size 10 in clothing, but has a 27-inch waist, choose the Large size Speedo instead of the Medium just in case.