No! Fitted diapers are a TYPE of diaper. See the FAQs in the tabs above for a low-down on the different types of diapers. One-size diapers are a SIZE of diaper.
Diapers generally come in two types of sizes: sized and one-size. Sized diapers fit a very specific, limited weight range. For instance, they might be available in x-small/newborn (fits 6 to 12 pounds), small (fits 8 to 16 pounds), medium (fits 15 to 22 lbs) and large (fits 22 to 30 pounds). All sized diapers have adjustable waist options to fit both skinny and chubby babies (either using a hook and loop closure or snaps); however, the rise is set. Because your child is constantly growing out of one size and into another, going the sized diaper route can be pricey. Because they don't have any extra fabric to deal with, they are usually quite trim.
One-size diapers (often abbreviated as OS) are designed to take a child through multiple weight ranges and stages and often claim to work from birth to potty training. One-size diapers have adjustable rises that allow the diaper to fit multiple weight ranges and child sizes.
They can go from very small to quite large:
A Rumparooz diaper on the smallest setting
A Rumparooz diaper on the largest setting
A Rumparooz snap diaper on the smallest setting (left) and largest setting (right).
The rise usually adjusts in one of three ways:
Snap-down rises are the most popular. They have multiple rows of snaps on the front of the diaper that allow you to snap down the front of the diaper to different size settings. To make the diaper the smallest, you would snap the top snaps to the very bottom snaps, causing the diaper to fold onto itself and become much smaller. To use it on the largest size, you just leave the rise snaps fully unsnapped. Here's an example on a BestBottoms diaper, showing the rise snaps fully unsnapped all the way to fully snapped down:
Some fold-down rises are snapless and must use a Snappi or diaper pins to close, as the SBish fitted below shows.
Toggle/button rises are the least common, used by only a couple brands. It's the hardest to explain! These don't have rise snaps, but rather allow you to adjust how tight the elastic is at the leg of the diaper, which also adjusts the rise by scrunching the diaper together and making it longer or shorter. In the picture of a FuzziBunz below, you can see the leg elastic sticking pulled out in the top picture, and if you look very closely at the bottom picture you can just barely see the hint of the elastic on both wings at the top of the diaper - this is how it looks for normal use when not being adjusted. You can pull this elastic tighter or make it looser to fit a variety of babies. This particular system uses buttons to lock the elastic in place; other systems might use toggles like you find on jackets.
Crossover tabs are another feature of many one-size diapers. To further the customization options of one-size diapers, most one-size diapers allow you to overlap the waist flaps to create a very small waist. You can see these crossover snaps in some of the pictures above, and below, you can see the wing has both male and female snaps that would allow the opposite wing to snap to this wing instead of the main part of the diaper.
In this Doodle Dype, you can see the white snaps on the bottom wing
that allow the top wing to snap onto it.
The crossover wings snapped at the smallest setting.
Aplix, or velcro, diapers usually also offer the option of crossover tabs. As you can see in the picture below, the velcro tabs are two-sided, allowing the tabs to be fastened to each other.
Many one-size diapers also offer multiple inserts that allow you to customize the absorbency (and therefore the bulk) depending on the age of the baby wearing it and how heavy of a wetter they are. Often this is in the form of a regular large insert paired with a smaller insert that can be used alone for newborns or with the larger insert overnight or for heavier wetters.
A bumGenius newborn insert/doubler (left) and regular insert (right)
Some all-in-one diapers such as the GroVia below have inserts that can be added and removed depending on the needs of your baby (you can see the smaller, snap-in insert laying across the bottom of the diaper).
Fitted diapers also usually offer a number of inserts and doublers. This Goodmama could be used alone, with the smaller insert alone, the larger insert alone, or both inserts.
This bitti tutto comes with three separate inserts that can be snapped together in a huge number of configurations to customize your diaper as needed.
So one-size diapers are GREAT, right?? One diaper to get me from birth to potty training? What a great investment! What a great amount of savings! How easy!!
Not so fast! One-size diapers ARE great and they do save a ton of money, and the vast majority of people use them for the bulk of their diaper stash. However, there are a few things to note:
1. One-size diapers will not fit newborns as a general rule. Despite the fact that they often claim to start fitting at 7 or 8 pounds, they usually will not fit a baby well until the baby hits around 10 or 12 pounds. If you have a very large, chubby newborn, you might be able to use them immediately, but don't count on it! If you are planning on having the majority of your stash made up of one-size diapers, you will need something different for the newborn stage. Many people use prefolds and covers during that time, since they're so cheap. Some people use disposables until their child fits into the one-size diapers. Some people buy x-small or newborn sized diapers. It's up to you! Note: Some brands do have one-size diapers that get much smaller than other one-size diapers. Rumparooz, Happy Heiny, and Softbums are brands that are known to get smaller than most of the other brands. However, that doesn't mean they'll fit your baby immediately - you still might run into fit issues even with them, so you still may need a newborn solution.
2. One-size diapers can be bulky on anything other than the largest setting (and very bulky on the smallest!). This might not mean anything to you, but some people are looking for trim diapers. Cloth diapers are already bulkier than disposable diapers, and one-size diapers are bulkier still, particularly when on the smallest rise. All that extra fabric has to go somewhere! If you're looking for trim, smooth diapers, you might want to consider sized diapers, or check out the review spreadsheet for one-size diapers that are rated highly for trimness (i.e. GroVia all-in-ones are known to be one of the trimmest one-size option).
3. One-size diapers may not last as long. Because they are used SO much and for SO long, one-size diapers may wear out faster than sized diapers. If you're going the one-size route, you may want to have a fairly large stash to spread out the wear and tear on the diapers (for instance, rather than using 12 diapers over and over and over, you could use 36 diapers in your rotation, which would mean each one is used less frequently).
If you like the idea of sized diapers but don't like the bulkiness or ill fit of one-size diapers, you can look for diapers that are hybrids. Some diaper companies, like AppleCheeks or Thirsties, have created diapers that come in two sizes, which offer a more customized fit (i.e. one size fits for 8 through 20 pounds, and the second size fits from 15 to 45 pounds) but also are slightly less bulky than one-size diapers. However, again, there's a drawback - both of those companies are known for having a fairly significant gap between sizes. While they claim to overlap, a baby who has outgrown their size one diaper may still be too small for their size two diaper.
Despite the drawbacks, one-size diapers are a popular, economical choice that work well for most people. Almost all brands offer a one-size diaper option. Check them out!