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Plus, a convenient size chart to keep on hand.

Becoming a new parent can be confusing enough; the last thing you should worry about is deciphering a diaper size chart to figure out which ones to stock up on. Babies go through thousands of diaper changes before potty training, so there's no doubt you'll be a diaper expert by the time you're through.

Until then, the parenting experts at the Good Housekeeping Institute break it down for you here. Our fiber scientists evaluate diapers in the Textiles Lab using a variety of absorbency tests, including how quickly each one can absorb fluid, how much liquid leaks off when the diaper's held at an angle, and how dry the surface stays when a weight is applied. We also send them home with parent testers to get in-depth, real-life feedback.

First things first: Diapers are sized by weight and not by age. Most babies will start in the Newborn size (which also has a cut-out in the front for the umbilical cord) then ultimately spend the majority of their diapering days in size 4, the most popular size on the market. Beyond that, there's no way to accurately predict ahead of time what size diapers your baby will be in at each age because babies grow at different rates. Still, it's safe to say babies will at least cycle through sizes 1, 2, and 3 during the first year.

Most disposable diaper brands are available in sizes Newborn through 6. On either end of the spectrum, Huggies and Pampers both offer a Preemie size for babies under six pounds, while Pampers even offers size 7 for toddlers over 41 pounds. Here is your ultimate diaper size chart based on the most popular, best performing diapers on the market:

Babies grow so quickly during the first year so they'll spend less overall time in the smaller-sized diapers, yet you'll use up more diapers when they're younger. Newborn babies can go through 12 diapers a day (that's 360 diapers in the first month!), but that drops down to 5-8 diapers per day by the end of the first year. Keep in mind: The smaller the diaper size, the more diapers you get in each box. Diaper packages may cost the same when you buy them, but you're paying slightly more per diaper as you size up.

You'll notice there's some overlap in weights between sizes. If your baby is in between and you truly can't decide, we recommend sizing down because the cost per diaper is less and a too-loose diaper can cause leaks. Still, your best bet is to pay close attention to when your baby is outgrowing their current size. Here's what to look out for:

Parents sometimes complain that Newborn diapers seem too small, yet Size 1 seems too big. If this is the case for you, try using Size 1 and folding down the waist before you put it on. You can also consider trying another brand; every baby is shaped differently and some brands may fit your little one better than others.

If you're looking for information on a specific diapers, here are the best performing and most popular options on the market, with the size charts exactly how they're shown on the brand's website:

Pampers is a Good Housekeeping Seal holder and has the most diaper sizes to choose from, with Preemie available in Pampers Swaddlers and Size 7 available in Pampers Cruisers. Though they're not as widely available, you can also get extended Preemie sizes P-2 for under 4 lbs and P-3 for under 1.8 lbs.

The brand also has the most diaper style options on the market, including Pampers Pure for a bigger focus on plant-based materials and Pampers Cruisers 360 Fit for active babies. Just note that size offerings will vary by style; for instance, Cruisers and 360 Fit start at Size 3 because they're designed for crawlers and walkers.

This is another popular choice (and one of our top-tested diaper brands) with lots of options to choose from. Diapers sizes range from Preemie to 6, but like Pampers they'll vary by style. Little Snugglers is the only diaper in Preemie and Newborn sizes, while Little Movers (for crawlers and walkers) start at Size 3.

Luvs is Pampers' more affordable sister brand. Unlike Pampers and Huggies, there's just one diaper style so you don't have to make the choice, and it's available in sizes Newborn through 6.

These diapers are popular for their fun prints and eco claims, plus they performed well in our test. There's just one style for daytime in a wide range of designs, plus an overnight option.

The brand is pricey per diaper, but it's a great choice if you prefer greener options because it has transparent claims and performed better than other "eco" brands. They're European, so make sure to check the size chart because it's entirely different from the others in this roundup.

The company has a big focus on sustainability for a variety of consumer products. The diapers are available in day or overnight, though they didn't perform quite as well as others in our test. Also note that the size chart differs slightly from some of the other popular brands, so double check before you buy.

This is a newer brand with tons of adorable prints, and it was one of the most absorbent diapers in our Lab's tests. They have two styles: A standard diaper and an overnight option. The size chart runs a little smaller than others, so this is another one where you'll want to review it carefully before you buy.

If you're confused on how to pick the size for a style of diapers that we haven't yet covered, here's the scoop: