How to Measure a Mattress: Width, Length & Depth
To measure a mattress, strip it bare and take three numbers with a rigid tape measure: width across the widest point from side seam to side seam, length from the head seam to the foot seam, and depth from the top sleeping surface straight down to the bottom of the mattress. Measure the mattress by itself — not the bed frame, not the foundation — and don't press the tape into the foam. Those three numbers tell you what size you own, what sheets will fit, and whether a new frame or base will work.
It sounds simple, and it mostly is. But a surprising number of returned sheets, too-small frames and "this doesn't fit" moments come from measuring the wrong thing. Here's how to get it right the first time.
What you'll need
- A rigid steel tape measure. A soft sewing tape sags and will read long.
- A second person, if you're measuring a king or California king. Long spans are hard to hold flat alone.
- A bare mattress. Take off the sheets, the protector and any topper first.
If you're measuring to replace a mattress, write the numbers down along with the brand and model printed on the law tag sewn to the side or foot of the mattress. That tag is the fastest way to confirm what you have.
How to measure a mattress, step by step
1. Measure the width
Run the tape across the mattress at its widest point, usually the middle of the bed rather than near the corners, which can round off slightly. Go from the outside edge of one side seam to the outside edge of the other. Keep the tape flat on the surface and straight — a diagonal reading will add inches that aren't there.
2. Measure the length
Measure from the outside edge of the head seam to the outside edge of the foot seam, down the center of the mattress. If the mattress is on a frame with a headboard, slide it away from the headboard first so you can get the tape to the true edge.
3. Measure the depth (height)
Stand the tape vertically against the side of the mattress. Measure from the highest point of the sleeping surface down to the bottom edge where it rests on the foundation. Two things matter here:
- Don't compress the surface. Rest the tape against the side, not on top of the quilting. Pressing down can cost you an inch or more on a pillow top.
- Include the pillow top or euro top. That padded layer is part of the mattress depth, and it's exactly the part that makes fitted sheets pop off in the night.
If you plan to add a topper later, note its thickness separately. It changes what sheets you need even though it isn't part of the mattress.
Standard mattress dimensions in the U.S.
Once you have your numbers, compare them against the standard sizes. Most mattresses sold in the United States land within an inch of these:
| Size | Width | Length |
|---|---|---|
| Twin | 38 in | 75 in |
| Twin XL | 38 in | 80 in |
| Full | 54 in | 75 in |
| Full XL | 54 in | 80 in |
| Queen | 60 in | 80 in |
| King | 76 in | 80 in |
| California King | 72 in | 84 in |
| Split King | two pieces, each 38 in | 80 in |
A few quick reads on your own measurement: if you got roughly 60 by 80, you have a queen. If it's 76 by 80, that's a standard king — narrower and longer means California king instead. If you measured about 38 inches wide, the length decides it: 75 inches is a twin, 80 inches is a twin XL. For a full breakdown of every size, including the less common ones, see our mattress dimensions and size guide.
Why your measurement might not match the chart exactly
Being an inch off from the standard number is normal and usually nothing to worry about. Common reasons:
- Manufacturing tolerance. Mattresses are sewn, not machined. Small variations between one unit and the next are expected, and covers can relax slightly over time.
- Age and wear. An older mattress may have spread at the edges or lost height in the middle. Measure a worn mattress at a few points and use the largest reading for width and length.
- Cover stretch. Knit covers give a little under the tape. Lay the tape on the surface without pulling it taut into the fabric.
- You measured the frame. Bed frames and foundations are often slightly larger than the mattress they hold. Always measure the mattress itself.
If your reading is off by several inches rather than one, you may have a specialty size — an RV mattress, an antique three-quarter bed, or an oversized king — rather than a standard one.
Measuring for sheets and protectors
Width and length pick the sheet size. Depth decides whether that sheet will actually stay on. Fitted sheets are sold with a maximum pocket depth, and a sheet built for a slim mattress will fight you every night on a tall one.
Standard-pocket fitted sheets commonly fit mattresses up to around 12 inches deep. Deep-pocket versions go further, and extra-deep options exist for the tallest pillow tops. Check the depth rating on the packaging against the number you measured, and add your topper's thickness if you use one. The same logic applies to a fitted mattress protector — browse sheet sets and mattress protectors by both size and depth rather than size alone.
Measuring for a frame, foundation, or adjustable base
When you're buying a platform bed, foundation or adjustable base, the mattress measurement is your starting point, but check two more things:
- Interior frame dimensions. Bed frames list an interior opening that the mattress sits inside. Compare that to your mattress width and length, not to the frame's exterior size.
- Total stacked height. Mattress depth plus foundation or base height gives you the height of the sleeping surface. Many people find it comfortable when the top of the mattress sits somewhere near hip height, making it easy to sit down and stand up without reaching.
Also measure your doorways, stairwells and hallway turns before a delivery. A queen mattress that fits the bedroom perfectly still has to get there.
Frequently asked questions
Should I measure a mattress with the sheets on?
No. Take everything off first, including the mattress protector and any topper. Bedding adds bulk and will make your measurement read larger than the mattress actually is.
Does mattress depth include the box spring or foundation?
No. Mattress depth is the mattress alone. Measure the foundation separately, then add the two together if you want to know the total height of your bed.
How do I measure a split king?
Measure one half. Each piece of a split king is a twin XL, so you should get about 38 by 80 inches per side. Placed together they cover the same footprint as a standard king.
My mattress measures between two standard sizes. What now?
Round to the nearest standard size when the difference is an inch or less, and shop that size. If you're several inches off, check the law tag for the model name and size — it may be an RV, bunk, daybed or specialty size that doesn't appear on the usual chart.
Do I need to measure for a mattress topper?
Toppers are sold by mattress size, so your width and length are what matter. Note the topper's own thickness, though, since it adds to the depth your fitted sheet has to cover.
Not sure what you measured?
Bring your numbers to us. At our Glendale showroom you can lie down on the sizes you're deciding between, compare depths side by side, and get a straight answer about what will fit your frame and your room. We serve Glendale, Burbank, Pasadena and the greater Los Angeles area, and delivery and setup in LA are free.
Every mattress we sell comes with a 120-night sleep trial, so you have real time at home to be sure. Start by browsing all mattresses, or come in and let us measure with you.