How to Measure Your Mattress for Sheets (Width, Length & Depth)

You ordered the right size on the label, the sheet arrived, and it still rides up at 2am or sits too shallow to tuck under. Nine times out of ten the problem isn't the size name, it's the depth. Here's how to measure your mattress for sheets the right way, so the set you buy actually stays put.

The three numbers that actually matter

Strip the bed down to the bare mattress first. Any topper, protector, or old sheet left on will throw your reading off. Grab a cloth or metal tape measure (not a ruler, you want one continuous pull) and take all three measurements at the widest, longest, and thickest points.

• ✓Width. Run the tape across the mattress from one side edge to the other. Measure near the middle, where it's fullest.
• ✓Length. From the head edge to the foot edge down the center. Pillow-top edges can round off, so pull snug to the true corner.
• ✓Depth. Stand the tape vertically against the side, from the top sleeping surface down to where the mattress stops and the box spring or platform begins. This is your mattress depth.

Write all three down in inches. Round up to the nearest half-inch rather than down, since a sheet that's a touch generous still fits, but one cut a hair short never will.

Depth is the number everyone skips

Width and length mostly follow the size name on the box. Depth doesn't. Two Queens can be 9 inches and 16 inches thick, and a sheet built for the shallow one will ping off the deep one by morning. If your fitted sheet keeps popping off, the pocket is almost always too small for your mattress depth. We dug into that exact failure in why a fitted sheet won't stay on.

Here's the rule that saves the reorder: your fitted sheet pocket should be your measured depth plus roughly 2 to 3 inches. That extra gives the elastic room to curl under the mattress and hold. Match the pocket to the depth exactly and it clings to the edge with nothing to grip; buy way too deep and it bunches. A little over is the sweet spot.

Pillow-top and hybrid mattresses are the usual reason people land in the deep or extra-deep rows without realizing it. If you're new to the term, our deep pocket sheets buying guide walks through when you actually need one.

Standard US mattress sizes to check against

Once you have your width and length, compare them to the standard chart below. If your numbers land within an inch of a row, that's your size and a stocked set will fit. If they're off by more than an inch or two, skip to the custom section.

Two traps worth flagging. King and California King are not interchangeable: a King is wider, a Cal King is longer, and swapping them leaves fabric flapping at one end. If you're torn between those two, our California King sheets guide lays out the difference. And anything bigger than a King, think Wyoming, Texas, or Alaskan King, lives in its own world of oversized bed sheets that standard retailers simply don't cut.

When your numbers don't match any standard size

RV mattresses, antique frames, boat berths, split adjustable bases, and oversized beds routinely land between the rows above. When that happens, buying the nearest size and hoping is how you end up with a drawer full of sheets that don't fit. The fix is to measure your mattress once, carefully, and order to those exact numbers.

That's the whole point of custom-made fitted sheets: you hand over your width, length, and depth, and the sheet is cut and sewn to them. If you want the matching flat sheet and pillowcases too, a full 600 thread count custom size sheet set covers the whole bed in the same cotton. Prefer just the fitted piece? The custom size fitted sheet is made to order on its own, and both carry a 100% Fit Guarantee, so if the numbers were right and it still doesn't fit, it gets remade.

Our Pick

600 Thread Count Cotton Custom Size Sheet Set

• Cut to your exact width, length, and depth
• Breathable 600TC Egyptian cotton, 9 colors
• 100% Fit Guarantee, remade if it doesn't fit

From $124.99

Shop the set

A few common questions

How do I measure my mattress for sheets?

Strip it bare and take three numbers with a tape measure: width across the middle, length head to foot, and depth from the top surface straight down to the base. Width and length give you the size; depth tells you the fitted sheet pocket you need.

What is mattress depth and why does it matter?

Mattress depth is how thick the mattress is, top to bottom. It decides whether a standard, deep pocket, or extra-deep sheet will stay on. Get it wrong and the sheet pops off the corners no matter how right the size name is.

Should a fitted sheet match my mattress depth exactly?

No, give yourself a margin. Choose a pocket about 2 to 3 inches deeper than your measured depth so the elastic can wrap under the mattress and grip. An exact match has nothing to tuck beneath.

What if my mattress doesn't match a standard size?

That's common with RV, boat, antique, and oversized beds. Measure all three dimensions and order custom size sheets made to those numbers instead of forcing the nearest stock size.