How this instrument works
Unlike shoe, ring, hat, or belt sizing, US mattress dimensions really are standardized — not by a government body, but by the Better Sleep Council, the consumer-education arm of ISPA (the International Sleep Products Association), the mattress industry's own trade group. Their published dimension table is what mattress manufacturers, box spring makers, and sheet and bedding companies all build against, which is exactly why a queen sheet set fits a queen mattress from any major US brand.
This calculator is a straightforward lookup against that table rather than a computed formula — there's no equation linking, say, 'Full' to 'Queen' the way there is between shoe sizes and foot length. Each named size (Twin, Twin XL, Full, Queen, King, California King, plus Crib/Toddler at the small end) simply corresponds to a fixed width and length in inches that the industry has converged on and largely stuck with for decades.
The one wrinkle worth knowing: 'standard' sizing is a US and Canada convention. Mattress dimensions in the UK, EU, Australia, and elsewhere follow entirely different naming and measurement systems (often metric, and not always corresponding cleanly to the same real-world size), so this table is specifically the North American consumer-mattress convention, not a global standard.
- Open the Mattress size dropdown.
- Select the size you're shopping for or comparing — Crib/Toddler, Twin, Twin XL, Full/Double, Queen, King, or California King.
- Read Width (inches) and Length (inches) — the standard dimensions for that size per the Better Sleep Council / ISPA table.
- Compare two sizes by selecting one, noting its dimensions, then switching the dropdown to the other.
- Double-check against the actual mattress or bed frame listing before buying — dimensions can run an inch or so off standard for specialty or imported models.
Worked example — comparing Queen to Twin and California King
Selecting Queen returns a width of 60 in and a length of 80 in — the most popular US mattress size for couples and larger bedrooms, per the Better Sleep Council table. Selecting Twin instead returns 38 in wide by 75 in long, five inches shorter than Queen and a full 22 in narrower, the standard choice for a single sleeper or a smaller bedroom.
California King, by contrast, returns 72 in wide by 84 in long — narrower than a standard King (76 in wide) but four inches longer, a shape historically favored for taller sleepers and rooms that are long and narrow rather than square.
Questions
Are US mattress sizes actually standardized, or does it vary by brand?
They're genuinely standardized across virtually all mainstream US mattress and bedding manufacturers, via the Better Sleep Council (ISPA's consumer-education arm) dimension table — that's exactly why a Queen fitted sheet from one store fits a Queen mattress bought from a completely different retailer. Specialty, imported, or older vintage mattresses can occasionally run slightly off these figures, but the named sizes (Twin, Full, Queen, King, and so on) are about as consistent as consumer product sizing gets in the US.
What's the actual size difference between King and California King?
Standard King is 76 in wide by 80 in long, while California King is 72 in wide by 84 in long — King is 4 in wider, California King is 4 in longer. King suits couples who want maximum shoulder-to-shoulder room, while California King suits taller sleepers or narrower, longer rooms where the extra length matters more than the extra width.
What's the difference between Twin and Twin XL?
Both are 38 in wide, but Twin XL is 80 in long versus Twin's 75 in — a 5-inch length difference that matters a lot for taller sleepers, which is why Twin XL is the standard size in most US college dorm rooms. Width-wise they're identical, so Twin XL sheets and bedding won't work on a standard Twin, and vice versa, despite how similar the names sound.
Does 'Full' mean the same thing as 'Double'?
Yes — Full and Double are two names for the exact same US mattress size, 53 in wide by 75 in long. 'Full' is the more common term in current US mattress retail, while 'Double' is an older term that's still used interchangeably, especially on furniture and bedding not specifically marketed as mattresses.
Are these sizes the same outside the US and Canada?
No — this table reflects the North American consumer-mattress convention specifically. The UK, most of continental Europe, Australia, and other regions use their own naming and metric-based dimension systems that don't map cleanly onto Twin, Full, Queen, and King, so if you're buying a mattress or bedding outside the US or Canada, check that region's own size chart rather than converting from this one.