Mattresses are standardized. A queen mattress is 60" × 80" whether you buy it in Portland or Miami. Duvet covers are not standardized at all, and most shoppers don't find that out until an insert arrives that doesn't fit.
This is a reference page. Below are the typical ranges by size, the real spread between brands, and the two numbers you should actually be shopping on.
Typical duvet cover dimensions in the US market
| Size | Mattress | Cover, typical range |
|---|---|---|
| Twin / Twin XL | 38" × 75" / 38" × 80" | 64"–70" × 88"–92" |
| Full / Queen | 54" × 75" / 60" × 80" | 88"–90" × 88"–92" |
| King / Cal King | 76" × 80" / 72" × 84" | 88"–106" × 94"–106" |
Those ranges are wide on purpose. They're wide in the market.
The same size name, three different products
Three brands, three Full/Queen covers, dimensions as published on their own product pages in August 2026:
| Brand | Twin / Twin XL | Full / Queen | King / Cal King |
|---|---|---|---|
| Piglet in Bed | 68" × 90" | 88" × 88" | 88" × 103" |
| Brooklinen | 64" × 90" | 90" × 90" | 90" × 106" |
| Parachute | 70" × 92" | 90" × 92" | 106" × 94" |
Read the king row twice. One brand's king is 88 inches wide and 103 long. Another's is 106 wide and 94 long: eighteen inches wider and nine inches shorter. They are not interchangeable, and both are correctly labeled "King."
The Full/Queen row is subtler and causes more returns: 88" × 88" versus 90" × 92" is a four-inch difference in length. Enough that an insert sized for one leaves visible slack in the other.
Why the spread exists
Two reasons.
The first is that European and American conventions collided. Many premium covers are woven and sewn in Portugal or Europe, where the standard sizes are metric and don't map cleanly onto Twin, Full, Queen, King. Brands convert, round, and pick a US label. Different brands round differently.
The second is mattress depth. Mattresses have gotten taller over the last fifteen years. Pillow-tops and hybrids routinely run 14 to 18 inches. Brands that design for a deep mattress add drape and end up with a bigger "queen" than brands that design for a 10-inch mattress.
The two numbers to shop on
Your insert, measured flat. Not the size printed on its tag. Lay it out, measure both directions, write it down, keep it in your phone.
The cover's stated finished dimensions. If a product page lists a size name and no inches, treat that as missing information and either ask or move on.
Match those two, allowing the cover to be equal to the insert or up to two inches smaller in each direction, and the fit will be right.
Sizing up on a deep mattress
If your mattress is 14 inches or taller, the standard advice is to go one size up on the bedding: a king cover and king insert on a queen bed. The extra width becomes drape instead of overhang, and the bed stops looking like the covers are being pulled toward whoever is closest to the edge.
Below 12 inches of mattress height, size normally. Going up will look sloppy rather than generous.
Twin versus Twin XL
Worth a line because dorms make it matter. A twin mattress is 75 inches long; a twin XL is 80. Most brands sell one cover labeled "Twin/Twin XL" that fits both, because five inches disappears into the drape. If you're buying for a college bed, buy the sheets by exact size, because that's where the five inches actually bites, and the duvet cover as Twin/Twin XL.
The one-line version
Size names tell you which bed. Inches tell you whether it fits. Shop on the inches.
Our duvet sets and sheets list finished dimensions in inches on every product page.