How to Measure Your Mattress for the Right Sheet Fit

You order a sheet set in what you think is your size, it arrives, and the fitted sheet either balloons loose or won't stretch over the corners. Nine times out of ten the problem isn't the sheet, it's the measurement. Learning how to measure your mattress for sheets takes about two minutes with a tape measure and saves you the return. Here's exactly what to measure and how to turn those numbers into the right size.

The three measurements that actually matter

A fitted sheet has to wrap three dimensions, so you need three numbers. Strip the bed down to the bare mattress first, because a mattress topper or pad changes the height you're fitting for.

Width and length set the size. Depth decides which deep pocket you need.

• ✓Width. Run the tape straight across the widest part, from one side edge to the other. Don't follow a sag or a curve, keep it flat.
• ✓Length. Measure head to foot down the center. Pillow tops sometimes round off at the ends, so measure the base, not the padding.
• ✓Depth. Stand the tape vertically at the side and measure from the bottom seam to the very top, including any pillow top or euro top. This is the number people skip, and it's the one that makes a fitted sheet pop off at 2 a.m.

Match your width and length to a size

US mattresses follow a set of standard sizes, so once you have width and length, you can usually name yours. Here are the common ones in inches:

A couple of things trip people up here. A California King is narrower but longer than a standard King, so the two are not interchangeable even though they sound close. And if your tape reads wider than 76 inches, you're likely on an oversized bed like a Wyoming, Texas, or Alaskan King, which standard packaging won't fit. For those, start at our oversized bed sheets collection. Want every size laid out side by side? Our bed sheet size chart is the full reference.

Why mattress depth is the number everyone gets wrong

Two Queen mattresses can share the same width and length and still need different sheets, because one is 9 inches tall and the other is a 16-inch pillow top. A fitted sheet is built with a set pocket depth, and if your mattress is taller than that pocket, the corners ride up and slip. That's the slipping-sheet problem in one sentence.

The fix is to buy a pocket that matches your mattress depth with a little room to spare. As a rule, pick a pocket depth equal to your mattress height plus one to two inches so the elastic has something to grip under the edge.

This is why our deep pocket fitted sheets come in 15, 18, and 21 inch options rather than one guess-and-hope depth. Measure once, pick the pocket that covers your height, and the sheet stays put. For a deeper dive on pockets and mattress height, see our deep pocket sheets guide.

When your numbers don't match any standard size

Some beds simply aren't built to a chart. Antique frames, European sizes, platform and daybeds, RV bunks, boat berths, and older heirloom mattresses often land an inch or three off every standard. If you've measured carefully and nothing on the list matches, that gap is real, not a mistake on your part.

That's the whole reason SGI makes custom size sheets. You send your exact width, length, and depth, and the set is cut and stitched to those numbers in the same 600 thread count cotton as the standard range. Not sure what to order for your bed? Our guide to ordering custom bed sheets walks through it, and every set comes with a fit guarantee so you're not gambling on your own tape reading.

Our Pick

600 Thread Count Cotton 4 Piece Sheet Set

• Eight standard sizes, Twin through California King plus RV King
• Nine colors, from White to Moss and Navy
• Breathable long-staple cotton, our best seller

From $48.99

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A few common questions

How do I measure my mattress for sheets?

Strip the bed to the bare mattress and take three measurements with a tape: width across, length head to foot, and height from the bottom seam to the top including any pillow top. Those three numbers tell you the size and the pocket depth you need.

What is mattress depth and why does it matter?

Mattress depth is how tall your mattress stands. It decides whether a fitted sheet's corners reach under the edge. Too shallow a pocket and the sheet slips off, which is the most common fit complaint there is.

What deep pocket size do I need?

Choose a pocket at least as deep as your mattress height plus an inch or two. For most standard mattresses a 15 inch pocket works, pillow tops usually want 18 inch, and very thick mattresses or ones with a topper added do best in 21 inch.

My measurements don't match any size on the chart. Now what?

That usually means an antique, European, RV, or boat bed that was never built to a US standard. Order a custom set cut to your exact width, length, and depth instead of forcing the nearest size.