How to Measure Mattress Depth Correctly for a Fitted Sheet

If a fitted sheet keeps pulling away from the corners, the problem may not be the bed size. The mattress may simply be deeper than the sheet is designed to cover.

To measure mattress depth, measure vertically from the bottom edge of the mattress to the highest point of the sleeping surface. If a mattress topper or substantial protector sits underneath your fitted sheet, include that extra height too.

It takes only a couple of minutes, but it can make the difference between a sheet that stays neatly in place and one that keeps working loose overnight.

What Is Mattress Depth?

Mattress depth is the mattress's vertical thickness. You may also see it described as mattress height or mattress thickness.

It is separate from bed size.

For example, two King mattresses can have the same length and width but very different depths. One may be relatively slim, while another has a pillow top, additional comfort layers or a separate topper that makes the complete sleeping surface much deeper.

That difference matters when buying a fitted sheet because the sheet has to reach down the sides of the mattress and fit securely around the corners.

How to Measure Mattress Depth

You do not need specialist equipment. A flexible tape measure is enough.

1. Remove the fitted sheet. Take off the existing sheet so you can see the mattress and any layers that normally sit underneath it.
2. Decide which layers the new sheet needs to cover. If your topper or substantial mattress protector sits underneath the fitted sheet every night, leave those layers in position or measure them separately.
3. Measure vertically from bottom to top. Place the end of the tape at the bottom edge of the mattress and measure straight upwards to the highest point. Do not wrap the tape around the side or press heavily into the mattress.
4. Add any extra bedding layers. If you measured the bare mattress separately, add the thickness of a topper or bulky protector that will sit beneath the fitted sheet.
5. Write down the total. Use this overall measurement when checking the depth information on the fitted-sheet product page.

For example, a 27 cm mattress with a 5 cm topper creates a total depth of approximately 32 cm. That 32 cm figure is more useful when choosing a fitted sheet than the mattress measurement alone.

Should You Include a Mattress Topper?

Yes, if the fitted sheet goes over it.

Imagine that your mattress is 25 cm deep and you add a 5 cm topper. Although the mattress itself hasn't changed, the fitted sheet now needs to cover about 30 cm of total height.

Ignoring the topper is a common reason a sheet may look like the right size but still feel unusually tight at the corners.

The important measurement, then, isn't always the mattress on its own. It is the total depth the fitted sheet has to cover.

Does a Mattress Protector Add to the Depth?

Sometimes.

A thin protector may add very little measurable height, while a thick quilted or padded protector can make a noticeable difference. If you regularly use a substantial protector underneath the fitted sheet, include it when measuring.

For example:

You do not need to overcomplicate small differences. The purpose is simply to avoid measuring a 28 cm mattress and forgetting several centimetres of bedding sitting on top of it.

Mattress Depth vs Fitted Sheet Pocket Depth

These two measurements are related, but not exactly the same.

Mattress depth tells you how thick your mattress setup is. Pocket depth describes the depth of the fitted sheet's side and corner construction.

You may see products described as standard, deep or extra deep, but those labels are not universal. One retailer's “deep” sheet can measure differently from another retailer's.

The centimetre measurement is therefore more useful than the name alone.

When comparing sheets, check what mattress depth the manufacturer says the product is intended to accommodate rather than assuming every “extra deep” sheet will fit the same mattress.

What Fitted Sheet Depth Do You Need?

Yorkshire Bedding currently offers fitted-sheet depth options of 25 cm, 30 cm and 40 cm.

A practical way to choose is to measure first and then select an option designed to accommodate at least that total depth.

Treat this as a shopping guide, not a universal industry rule. Fitted-sheet construction, elasticity and recommended maximum mattress depth can differ between manufacturers.

If your measurement sits very close to the limit of a particular sheet, check the product specification rather than automatically choosing by the “deep” or “extra deep” label.

Why Mattress Depth Can Make a Fitted Sheet Come Off

When the sheet pocket isn't deep enough, the fabric may struggle to reach properly around the mattress and under the corners. Movement during the night can then gradually pull one corner free.

Mattress depth is not the only possible cause. Worn elastic, the wrong width or length, or a poorly fitted sheet can also cause movement.

This article should answer the measurement question, while Yorkshire Bedding's separate guide on how to stop fitted sheets from coming off covers the wider troubleshooting side in more detail.

Mattress Depth Is Different From Mattress Size

A bed size such as Single, Double, King or Super King mainly tells you the mattress width and length. It does not tell you how thick the mattress is.

That means choosing a fitted sheet involves two separate checks:

First: choose the correct bed size.

Second: choose a depth that suits the mattress and any layers underneath the sheet.

A King fitted sheet with the wrong depth can still fit poorly even when its width and length are correct.

Yorkshire Bedding's separate UK bed size guide is the better place to check standard mattress widths and lengths rather than repeating the full size chart here.

How to Measure a Pillow-Top Mattress

Pillow-top mattresses can be slightly more awkward because the upper surface is rounded rather than completely flat.

Measure from the bottom edge of the mattress to the highest natural point of the pillow top. Do not press down on the upper layer to make the measurement smaller.

If the surface varies slightly, measure near the centre and at one or two other points. Use the largest realistic measurement when checking the sheet specification. Shop Filled Bounce Pillows from Yorkshire Bedding.

What If the Mattress Has Rounded or Padded Edges?

You still want the vertical height, not a measurement following the curve of the mattress.

Hold the tape straight from the bottom edge towards the upper sleeping surface. If needed, place something flat, such as a ruler, across the top of the mattress and measure to the underside of that straight edge.

This can be useful on very soft mattresses where it is difficult to see exactly where the highest point sits.

Common Mattress-Depth Measuring Mistakes

The most common problem is measuring only the bare mattress when a thick topper normally sits underneath the fitted sheet. This can make the final measurement several centimetres too small.

Another mistake is measuring around the mattress rather than straight up its side. Mattress depth is a vertical measurement, not part of the mattress circumference.

It is also easy to assume that all mattresses with the same bed-size name have the same depth. A King mattress can be 25 cm deep, 30 cm deep or considerably thicker while still being a King.

Finally, do not automatically buy the deepest sheet available. A sheet that is much deeper than the mattress may leave excess fabric underneath or create a looser fit than necessary.

A Simple Real-World Example

Suppose you have a King mattress measuring 28 cm deep. On top of it sits a 5 cm topper and a padded protector that adds about 1 cm.

Your total is:

28 cm + 5 cm + 1 cm = 34 cm

The width and length still require a King fitted sheet, but the depth selection now needs to accommodate around 34 cm.

Within Yorkshire Bedding's current fitted-sheet range, the 40 cm depth option is the relevant one to investigate, rather than choosing solely from the King-size label.

Do You Need Extra Depth for Tucking Under the Mattress?

A fitted sheet needs enough fabric and elasticity to sit securely around the corners, but you should not invent your own fixed extra allowance such as “always add 5 cm”.

Manufacturers construct sheets differently. A product labelled as suitable for a particular mattress depth should already be designed with its intended fit in mind.

Measure the setup accurately and compare your result with the manufacturer's stated depth or fit guidance. That is more reliable than adding an arbitrary number of centimetres. Shop waterproof mattress protectors from Yorkshire Bedding.

What If Your Mattress Is Between Two Sheet Depths?

If the mattress setup is deeper than one option's stated limit, move to the next suitable depth rather than forcing the smaller sheet over the mattress.

For example, if your complete setup measures around 28 cm, a product intended only for mattresses up to 25 cm is unlikely to be the best choice. A 30 cm option is more appropriate to investigate.

If you are sitting directly on a product's maximum measurement, read its specific sizing information carefully because fabric stretch and construction can vary.

Frequently Asked Questions

How do I measure mattress depth?

Measure vertically from the bottom edge of the mattress to the highest point of the sleeping surface. Keep the tape straight and avoid compressing the mattress.

Do I include a mattress topper when measuring?

Yes, if the fitted sheet sits over the topper. Either leave it in place while measuring or add its thickness to the bare mattress measurement.

Is mattress depth the same as mattress thickness?

In bedding terminology, mattress depth, height, and thickness generally refer to the mattress's vertical measurement.

What is fitted sheet pocket depth?

Pocket depth refers to the depth around the fitted sheet's sides and corners. Check the manufacturer's specification to see what mattress depth the sheet is designed to fit.

What depth fitted sheet do I need for a 30 cm mattress?

Start by checking whether a topper or thick protector increases the total measurement beyond 30 cm. If the complete setup remains around 30 cm, look for a fitted sheet specifically designed to accommodate that depth.

Why does my fitted sheet keep coming off?

A sheet that is too shallow for the mattress is one possible cause. The wrong bed size, worn elastic and an unusually loose fit can also make the corners come free.

Can I put a 40 cm fitted sheet on a 25 cm mattress?

It may physically fit, but considerably more depth than you need can leave excess fabric and a less secure finish. A depth closer to your measured mattress generally gives a neater fit.

Should I measure my mattress before buying every fitted sheet?

It is worth measuring whenever you change mattresses, add a topper or buy from a range with different pocket depths. Once you know your current setup, you can keep the measurement for future purchases.

Measure First, Then Choose the Sheet

Mattress depth is easy to overlook because most bedding shopping starts with familiar labels such as Single, Double or King. Those labels tell you the bed's footprint, but they don't tell you whether the fitted sheet will reach comfortably around the sides.

Measure from the bottom of the mattress to the highest point, include any topper or substantial protector that sits beneath the sheet, and use the total when comparing product specifications.

Yorkshire Bedding's current fitted sheet collection includes 25 cm, 30 cm and 40 cm depth options, giving you a choice for standard and deeper mattress setups.

Getting those few centimetres right can save you from repeatedly pulling the same fitted-sheet corner back into place.