People measure a mattress for one of four reasons: buying sheets that actually fit, buying a frame or foundation, replacing the mattress with the same size, or working out whether it will get up the stairwell. Each of those needs a slightly different number, and the most common mistake is taking one measurement and using it for all four.
It takes about three minutes to do properly. Here is the method, the standard sizes to check against, and the reasons a perfectly normal mattress often measures an inch off the number on the label.
What you need
A retractable tape measure, and a second person if the mattress is a queen or larger. A cloth tape works but sags across a wide span, which is where half-inch errors come from. Strip the bed completely first. Measuring over a fitted sheet, a pad or a protector adds thickness you will then buy sheets around, and the sheets will be loose.
Step by step
- Measure the width. Run the tape across the shortest side, from the outer edge of one side panel to the outer edge of the other. Measure across the middle of the mattress, not near the corners, where the edges round off and read short.
- Measure the length. Same principle along the long side, head to foot, outer edge to outer edge.
- Measure the depth. Stand the tape vertically against the side panel, from the bottom seam to the highest point of the top surface. Do not press the tape into the foam. On a pillow top, measure to the top of the pillow top, not to the seam below it. This is the number that determines whether your sheets will stay on.
- Write down all three. Width by length by depth, in that order, which is how sheets, protectors and frames are all listed.
If you are measuring to move the mattress rather than to dress it, add the diagonal: measure corner to corner across the face. That is the number that decides whether it turns a tight landing, and it is the one people forget.
Standard US mattress sizes
| Size | Width | Length |
|---|---|---|
| Crib | 28 in | 52 in |
| Twin | 38 in | 75 in |
| Twin XL | 38 in | 80 in |
| Full (double) | 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 |
Depth is not standardized at all. Mattresses run anywhere from around 6 inches for a thin foam model up to 15 inches or more for a pillow top hybrid, which is why depth is the measurement that trips people up. Our mattress thickness guide covers what different profiles mean for comfort and support.
Why your mattress does not match the chart
A queen that measures 59.5 inches instead of 60 is not defective. Three things cause this legitimately:
- Manufacturing tolerance. An inch of variance either way is normal and accepted across the industry. Cover fabric, quilting and how tightly the panel is sewn all move the outside dimension slightly.
- Age and compression. A mattress that has been slept on for years compresses at the edges and the foam layers settle. An older bed commonly reads a little smaller than it did new.
- Temperature. Foam is softer when warm and firmer when cold, which changes how the side panel holds its shape. Measuring a mattress in a hot LA bedroom in August and again in January can genuinely produce different numbers.
If your measurement is within an inch of a standard size, treat it as that size when buying sheets and frames. If it is off by more than two inches, you likely have a non-standard size: an RV or camper short queen, a full XL, an antique frame size, or an imported mattress built to metric dimensions.
Which measurement to use for what
Buying sheets
Width and length tell you the size to buy. Depth tells you whether to buy standard or deep pocket. As a rule, a mattress over about 14 inches deep needs deep pocket sheets, and if you use a topper or a thick protector, add that thickness before deciding. Sheets that are barely deep enough pop off the corners within a week.
Buying a frame or foundation
Use width and length only. Frames are built to the nominal size, not to your particular mattress, so a queen frame takes a queen mattress even if yours measures a half inch under. What you actually need to check is the room, not the mattress: see how to measure your room for a bed frame and mattress before you commit to a size upgrade.
Replacing the mattress
Measure the existing one, then check it against the chart above rather than ordering by your measurement. Order the standard size your mattress is closest to. Ordering a custom dimension because your old bed read 59.5 inches creates a mattress no standard sheet will ever fit.
Getting it through the door
Depth and diagonal. A 14 inch pillow top hybrid is rigid and does not flex the way a thinner foam mattress does, which is what makes tight staircases and older LA apartment hallways a problem. Worth measuring before delivery day rather than during it.
Frequently asked questions
What are the measurements of a queen size mattress?
A standard queen is 60 inches wide by 80 inches long. Depth varies by model, commonly between 10 and 14 inches. A short queen, used in RVs and campers, is 60 by 75 inches and is not interchangeable with a standard queen for bedding.
What are the measurements of a king size mattress?
A standard king is 76 inches wide by 80 inches long, which is the same length as a queen and 16 inches wider. A California king is different: 72 inches wide by 84 inches long, so it is narrower but four inches longer. Neither uses the other's sheets.
What are the measurements of a full size mattress?
A full, also called a double, is 54 inches wide by 75 inches long. That is 16 inches wider than a twin but the same length, which is why taller adults often find a full too short even though it is wide enough. A full XL adds five inches of length at 54 by 80 inches.
What are the measurements of a twin mattress?
A standard twin is 38 inches wide by 75 inches long. A twin XL is the same width at 38 inches but 80 inches long, matching the length of a queen or king, which is why twin XL is the size used for split king adjustable setups and most college dorms.
What are the measurements of a crib mattress?
A standard full size crib mattress is 28 inches wide by 52 inches long, and no more than 6 inches thick. These dimensions are regulated for safety, and the gap between the mattress and the crib frame should be small enough that two fingers do not fit between them.
How do you measure a mattress for sheets?
Strip the bed, measure width and length across the middle of the mattress from outer edge to outer edge, then measure depth vertically from the bottom seam to the highest point of the surface, including any pillow top. Buy sheets by the width and length, and choose standard or deep pocket based on the depth plus anything you layer on top.
If the measurement is telling you it is time
A mattress that now measures noticeably smaller than it did, with edges that have lost their shape, is usually a mattress near the end of its useful life. Sheets slipping off corners that used to hold is often the first sign, before anyone notices the comfort has changed.
If that sounds familiar, browse twin sizes or full sizes, or take our sleep quiz for a firmness recommendation. We have five showrooms across Los Angeles, same-day delivery in much of the city, and a free 120-night comfort guarantee, so you can settle the size and firmness question at home rather than in a store aisle.
