A swim diaper should fit snugly at the legs and waist with no gaps, because its job is to contain solids in the water, not to absorb. Check your child's current weight against the maker's size chart, then check the fit on your child. If you are between sizes, let the leg seal decide rather than the number on the label.
Why fit matters more than absorbency
An everyday diaper is built to absorb. A swim diaper is not, so it relies on a close seal at the leg openings and waistband. A gap at the leg is where a leak starts, and a band that digs in is uncomfortable for your child. That is why size matters so much here.
Reading a swim diaper size chart
Charts list a weight range for each size and sometimes an age. Weight is the more useful number, because children of the same age vary a lot. Use a recent weight from a check-up or a home scale, and read the chart for the exact product you are buying.
Labels differ between brands. A Small from one maker may not match a Small from another, and the names themselves vary:
- Some show a weight range, such as the Charlie Banana Reusable Swim Diaper with Snaps, Seally, Large (22-34 lb).
- Some use age, such as the Splash About Happy Nappy Reusable Swim Diaper, Strawberry Field, 12-24 Months.
- Some show only a letter or name, so open the product page for the weight range.
Our diaper sizing guide covers everyday sizes, but swim sizes have their own ranges, so use the swim chart on the product page.
Checking the legs and waist
Dress your child in the swim diaper and look at three places:
- Legs. The leg openings should sit snugly against the thighs with no gaps you can see.
- Waist. The band should be snug at the belly, and you should be able to slip a finger under it without a struggle.
- Rise. The front and back should cover properly and not ride low as your child moves.
If your child is walking, ask them to stand, sit and squat, then look again. For a baby, look again while you hold them upright. Check once more after the swim by looking for deep marks or red lines where the elastic sits. If your child's skin looks sore or irritated, ask your doctor, nurse or pharmacist.
Between sizes: which way to go
When your child's weight sits on the boundary of two sizes, work through these questions:
- Does the smaller size close easily and leave no marks? Then stay with it.
- Does the smaller size leave marks, or is it hard to pull over the thighs? Go up.
- Does the larger size gap at the legs even when it is on its snuggest setting? Stay in the smaller size, or wait until your child grows.
Do not size up just to get more wear out of a diaper. A gap at the leg defeats the purpose, however many months the diaper lasts. If your child is growing quickly, an adjustable style may give you a little more room.
Adjustable snaps vs pull-on styles
Some swim diapers fasten at the sides with snaps, tabs or a drawstring waist, and some pull on like underwear.
- Snaps, tabs or drawstrings can be adjusted for fit and opened for changing. That helps with a baby who is lying down or a child who is not yet standing steady.
- Pull-on styles slide on quickly for a child who stands, but a soiled one must be slid down the legs, so keep wipes and a spare change of clothes close.
The product page shows how each one fastens, and our swim diapers collection lists the options.
Signs it is time to size up
- Leaks at the legs even when the diaper is freshly on
- Marks or red lines at the waist or legs after a swim
- Snaps or tabs on their last position, or a diaper that no longer closes
- The diaper is hard to pull on, or it rides low
- Your child's weight is at or above the top of the chart
Before you size up, rule out other causes. A diaper that went on twisted, or with a leg edge tucked under, can gap as well, so straighten it and look again. Then recheck the weight and the chart.
Shop this guide
- Reusable Swim Diaper with Drawstring, Gone Safari, Size L (22-34 lbs) (ships via Amazon)
- Charlie Banana Reusable Swim Diaper with Drawstring, The Whale on White, Medium (ships via Amazon)
- Reusable Swim Diaper with Snaps, Hello Sunshine, Size L (22-34 lbs) (ships via Amazon)
- ALVABABY Cloth Diaper Cover, 3-Pack, Swim Diaper (ships via Amazon)
- See all: Swim Diapers
Prices are on each product page. Free shipping on orders of $100 or more within Canada.
Sizing for older and bigger children
Some swim diapers come in larger sizes. Open the product page and check the full range of sizes, because the top end varies by brand. One product in a size labelled Large is the Babygoal Reusable Swim Diapers, Large, Shark & Tortoise, 3 Pack. Check its page for the weight range, and confirm that it reaches your child's weight before you order. If a chart lists waist or thigh measurements as well as weight, measure with a soft tape, because measurements can tell you more than weight alone for an older child.
For an older child, let them help choose the style, and pack a change of clothes so they can change in private. If your child needs leak protection for swimming for a medical reason, ask their doctor or nurse what is suitable, and check the facility's rules before you go.
Common questions
Is a swim diaper the same size as my child's regular diaper?
Not always. Swim diapers have their own weight ranges, so use the swim chart for the product you are buying.
How often should I recheck the size?
At the start of each swim season and again every few weeks if your child is growing quickly.
Do disposable and reusable swim diapers use the same sizes?
Not necessarily. Each product has its own chart, so check both if you plan to use both types.
Not sure which size to order? Use our contact page with your child's weight and the product you are looking at, and we will help you choose. We reply within one business day.