'I bought the wrong mattress size — what should I do now?' 3 steps to take

A woman and man lie together on a amattress that's the wrong size, he's taking up all the space on the right while she's squeezed onto the left
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When buying a new mattress, choosing the right size for your bed frame and sleep needs is one of the first big decisions you'll need to make. So what happens if you order a mattress in the wrong size? While it's an easy mistake to make, solving the problem can be a little more complicated than you think.

Buying the best mattress for your sleep needs and budget is an investment so you need to get it right in terms of the support and comfort it offers, and also the size. The good news is that most mattress manufacturers and retailers offer a trial period and returns, but the terms of those vary brand to brand.

Here we'll explore what you can do if you have bought the wrong mattress size, plus our top tips for choosing the right size mattress (including what to consider) in the future.

What to do if you've bought the wrong mattress size

1. Check the return policy / trial period

Have you unrolled your mattress-in-a-box only to find it doesn't fit your bed frame? The first thing to do is check the mattress trial and return policy. A sleep trial allows you to test the bed at home to see if it suits your needs, and that includes whether it's the right mattress size or not.

We recommend ordering a mattress direct from the retailer, as this typically gets you the best benefits and the longest trial. Buying from the brand also tends to come with the best aftercare – good news if you need to exchange a wrong size mattress. 

However, some mattresses can't be returned, or can't be returned if removed from the packaging. We'll cover what to do in these scenarios below. Also, keep in mind some brands do have a returns fee (typically small in comparison to the full cost of the mattress).

Two delivery men take a mattress that is being returned and carry it to a white van

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2. Replace your bed frame

Ordering the wrong mattress size can sometimes be a happy accident, as you might discover this new queen size suits your needs better than the full you had before. However, your new mattress still needs a supportive base, which means you'll have to replace your old bed frame with one in the new size.

A bed frame should be replaced semi-regularly, with a good bed frame generally lasting 10 to 15 years. So buying a mattress in the wrong size could be an unexpected opportunity to upgrade your entire setup. However, a new bed frame might also be a necessary compromise if your mattress doesn't have a a trial period or you missed the return window. 

3. Check your donation options

If you're unable to return the bed and it isn't the right size for your needs, the best thing to do is sell or donate your old mattress. We have some advice on how to get rid of an old mattress, and while this can be a complex process, it's much easier to find someone to take a fresh-out-the-box mattress than one you've been sleeping on. 

Alternatively, you can consider recycling your mattress. There are organizations that allow you to responsibly dispose of an old mattress, so you know your small mistake is going to good use. And once your old bed is sorted, follow the advice below to avoid the same thing happening when you shop for its replacement in the mattress sales

Two men dressed in delivery clothing install a new mattress in a bedroom, placing it on the bed frame

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3 tips to get the right mattress size next time

1. Measure everything twice

Before ordering a new bed, double check the measurements of your current mattress and the bed frame it's sitting on. Make a note of the measurements – and then check again. 

Next, check the measurements of the mattress you want to order. Mattress sizes are the same across brands (a queen is a queen no matter where you shop), but it's worth cross-checking to avoid mistakes.

This step is even more necessary if you're buying from an international site. US, UK, and EU standard bed sizes are different. So a king Nectar Memory Foam Mattress US and a king Nectar Memory Foam Mattress UK won't measure up the same. 

2. Double check the trial and returns policy

A good trial and return period is the easiest way to deal with a mattress that doesn't meet your needs, whether it's too firm for your side sleeping partner or too big for your queen size bed frame. The trial period and return policy should be clearly displayed on the brand site, but check the small print to make sure you haven't missed anything. 

Be aware that if you're buying from a third party retailer, the trial period might be shorter or, in some cases, non-existent. That doesn't mean you shouldn't buy the mattress, it just means that once you've unboxed the bed, you're stuck with it. 

A woman with dark hair lies in bed yawning because she is so tired and ready to sleep

(Image credit: Getty Images)

3. Familiarize yourself with common bed sizes

Convinced you and your family have been cuddling up in a king, only to find you've been squeezing into the best queen mattress? A mattress can last for up to 10 years (even longer, if you've invested in a latex mattress) so it's easy to forget what size you ordered a decade ago.

Familiarizing yourself with common bed sizes can not only prevent you from ordering the wrong size, but also ensures your mattress meets your needs. You might debate between a king vs a queen mattress, or wonder if a full vs a queen mattress is better for your small home? Each mattress size has its own benefits, so familiarize yourself with them before clicking 'add to cart'.

Ruth Jones
Sleep staff Writer

Ruth Jones has recently joined the Tom's Guide team as a sleep staff writer, covering all things mattresses and sleep. Ruth previously worked as a sleep and mattress writer for our sister website TechRadar, and has a deep interest in sleep and how it affects our day to day wellbeing. Ruth is a self-confessed stomach sleeper with a penchant for medium-firm mattresses, and also loves a good eye mask for helping her to fall asleep easier at night.