What size is a king-size mattress topper? Expert-approved dimensions for optimum support

Professionals address one of the most important mattress topper questions – so you can find the perfect fit for a restful slumber

What size is a king-size mattress topper? Bedroom with blue velvet headboard, dark wood bedside table, table lamp with blue shade, bedding with blue patterned cushion, pink throw
(Image credit: ANNA STATHAKI)

What size is a king-size mattress topper? This answer may appear seemingly straightforward, but it is not as simple as it initially appears. 

The process of choosing the best mattress topper for your king-size mattress comes with hidden complexities – from measuring the right thickness to finding the right depth.  Finding the right mattress topper can not only add the final flourish to one of the best mattresses, it can offer comforting support and help with the protection and longevity of your mattress.

So, exactly what size is a king-size mattress topper? Here is what the sleep experts want you to know before investing in the right one for you.

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(Image credit: Future / Chris Everard)

What size is a king-size mattress topper? 

According to Logan Foley, Sleep Science Coach and Managing Editor at The Sleep Foundation, a king-size mattress topper is the same size as the mattress – 76 x 80 inches. 'For the most use and comfortability in your mattress topper, it is important to measure the size of your mattress and match your desired topper to it,' she says.

If your topper is smaller than the mattress, you will end up with ridges and bumps at the side of your bed. And if the topper is too large, it will overhang your bed – and taint your tidy bedroom ideas in the process.  

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(Image credit: Future/ Mary Wadsworth)

How many inches of a mattress topper is best?

'Most mattress toppers add 1.5 to 4 inches of thickness, so regular sheets may not fit right,' Logan says.  The expert adds that deep pocket sheets are deeper than average, making it easier to stretch and cover mattresses with toppers. 

Emily Johnstone from Best Mattress For You adds that if you mismeasure the mattress topper's thickness, it will be less ineffective and may even lead to the need for a new mattress.

Do you need larger sheets with a mattress topper?

The question as to whether you need larger sheets with a mattress topper depends on the depth of the mattress on which the topper will sit.

'If the mattress is a standard 10-12 inch height, your current sheets should be deep enough to accommodate the topper, but if the mattress is taller, [for example] 14 inches or more, you may need to get a deeper pocket fitted sheet to cover everything without it being a strain,' Emily explains. 

If you prefer the feel of a thicker mattress pad, Pavel Ufimtsev, Certified Sleep Science Coach and Co-Founder of Sleep Matters, recommends using a fitted sheet with deeper pockets alongside your topper. This will stretch over the mattress and ensure it doesn't slip off throughout the night.

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(Image credit: Richard Gadsby)

What depths do mattress toppers come in?

Pavel explains that most toppers have between 16 to 22 inches of depth to ensure they stay put on your mattress. But how can you find the one for you? The expert suggests measuring the depth of the top of the mattress pad to the base of the mattress – to determine the size of deep fitted sheets you need. 

'It's also important to avoid drying the fitted sheet too long with each wash to prevent the fabric from shrinking, which can make it fit too tight over the mattress topper and mattress.'

So, whether you're looking to protect your organic mattress from spills – or you're looking to prevent lumps and bumps from tainting your scheme – these tips will offer the support and the aesthetic you desire. 

When should you buy a mattress topper?

Many of us buy a mattress topper as soon as we purchase a new mattress, adding an enhanced layer of protection, comfort, softness and support – this can also help to prolong your mattress life right from the start.

If you don't have a mattress topper, and have had your mattress for a few years, now could be the best time to buy. Using a mattress topper is a great way to revive an older mattress before purchasing a new one. If your mattress is starting to sag or is no longer as soft or as firm as when you first purchased, it is definitely worth trying a mattress topper to see if that makes a difference.

When deciding if and when to buy a mattress topper, it is all about subjective comfort, and what you want out of both your mattress and mattress topper.

Best places to shop king-size mattress toppers:

Megan Slack
Head of Celebrity Style News

Megan is the Head of Celebrity Style News at Homes & Gardens. She first joined Future Plc as a News Writer across their interiors titles, including Livingetc and Real Homes, before becoming H&G's News Editor in April 2022. She now leads the Celebrity/ News team. Before joining Future, Megan worked as a News Explainer at The Telegraph, following her MA in International Journalism at the University of Leeds. During her BA in English Literature and Creative Writing, she gained writing experience in the US while studying in New York. Megan also focused on travel writing during her time living in Paris, where she produced content for a French travel site. She currently lives in London with her antique typewriter and an expansive collection of houseplants.