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

Professionals address the important mattress topper questions – for the perfect fit that promotes a premium slumber

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

So, exactly what size is a king-size mattress topper? And how can you ensure you ensure you protect your best mattress in style? Here is what the sleep experts want you to know before investing in the right one for you.

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What size is a king-size mattress topper? 

According to Logan Foley (opens in new tab), 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 (opens in new tab) 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 (opens in new tab), 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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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. 

Megan Slack
News Editor

Megan is the News and Trends Editor at Homes & Gardens. She first joined Future Plc as a News Writer across their interiors titles, including Livingetc and Real Homes. As the News Editor, she often focuses on emerging microtrends, sleep and wellbeing stories, and celebrity-focused pieces. 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.