What Size is a King Size Mattress? Our Guide to King Beds and Mattresses

A king size mattress is the perfect choice for a couple who love to share a bed but who each want plenty of space to spread out and move around, without disturbing each other’s sleep. But exactly how big is a king mattress, and will it fit in your bedroom?

At 76in (6ft 4in) wide by 80in (6ft 8in) long, the US king mattress is pretty huge. It’s big enough to accommodate couples who share the bed with their children or pets (or both), and it also feels luxurious – like a hotel bed in your very own home.

The main downside of a king size bed is that you need a king size room to fit it into, preferably one measuring at least 12 x 12ft. A king size mattress is also much heavier and more tricky to maneuver than a full or queen size model – and, of course, it costs more.

Below, we look at the pros and cons of a king size mattress, and reveal how it measures up against other US mattress sizes, including queen size and California king. After reading, we hope you’ll have a better idea of the ideal mattress size for you, your partner, your home and your budget.

How big is a king size mattress?

King size mattresses measure 76 x 80in, making them the largest standard mattress size you can buy in the US. A US king mattress is significantly bigger than a UK king (60 x 78in) and a US queen (60 x 80in); it’s effectively the same size as pushing two twin XL (38 x 80in) beds together – but without the uncomfortable gap down the middle.

These dimensions make for an ample surface area of 6,080 square inches, which is well over 6ft by 6ft. While that’s great news for couples who want peace while they sleep, or even for solo sleepers who love to spread out, it does take up a significant amount of floor space.

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What are the pros and cons of a king size mattress?

Here’s a quick summary of the main advantages of king size beds:

• The sleeping surface is sufficiently ample to enable a couple to turn and stretch in the night without knocking into each other, so both can get a better night’s sleep;

• The whole family can climb in, pets included, and there’s plenty of room for books, laptops and breakfast trays;

• King size offers decent space for a larger person or larger couple to sleep in comfort;

• King size makes a magnificent style statement in your home, whether you’re a solo sleeper or a couple.

These luxurious mattresses have their tradeoffs, however:

• They take up a lot of floor space, including room to open drawers and move around the bed comfortably;

• A king size mattress is big and heavy (140lb for the king size Purple Mattress, for instance), making it hard to lift, turn and maneuver. If you’re having your mattress delivered, make sure it’s delivered all the way to your bedroom.

• King size costs significantly more than full or queen size, and that’s before you’ve considered the budget for a king size bed frame and bedding, which is also more expensive.

What about queen size and California king size?

Queen size is smaller than king size, without being so small that it feels like a bed for a solo sleeper. At 60 x 80in, a queen mattress is roughly the same size as a UK king size (60 x 78in), and provides plenty of room for a couple to sleep without disturbing each other; but it doesn’t cost as much as a king size or take up as much room. Queen will likely be a smart choice for many homes and couples.

However, if you find queen size a little too small, but your room can’t quite accommodate the width of king size, then the Olympic queen may be an even smarter choice. At 60 x 80in, it offers plenty of space without being quite as room-hogging as a king size. However, Olympic queen isn’t widely available size for mattresses, beds and bedding, so you may end up paying a lot more for it.

If you’re tall and you find that even king size mattresses give you cold feet, and you don’t mind sacrificing a bit of width for the two of you to spread out, then California king size may be the best option for you. At 72 x 84in, the “Cali king” is narrower and longer than the standard king, but its surface area is similar and it will comfortably fit a couple. It’s very widely available, and usually costs around the same as a king size.

Here’s how all the standard US mattress sizes compare:

*these sizes don’t have to be made to order, but they’re harder to find

How much does a king size mattress cost?

A king size mattress costs more than a smaller mattress, but it’s an investment. You stand to enjoy the extra space and luxury it provides for many years to come – and if you sleep with a partner, it will help both of you to sleep better than if you were in a cheaper queen or full size bed. You may decide that’s worth paying for.

Prices for the best king size mattress range from around $1,500 to $2,000. They tend to be around 20-25% more expensive than queen size, and 30% more than full size.

For instance, the bestselling Purple Mattress costs $1,999 in king size, compared with $1,499 for queen size and $1,399 for full size.

Casper’s The One all-foam mattress is a little cheaper, at $1,745 for a king size, $1,245 for a queen size, and $1,125 for a full size.

Cheaper still is the Emma Original, which costs $1,459 for king size, and $979 for a full size. Like most mattress brands, Emma regularly runs discount sales that can save you 50% off the price of your mattress.

Remember that your new mattress will need a bed frame and bedding, too. King size sheets and bed frames tend to cost around 10% more than for queen. Crate & Barrel’s Cozysoft Organic Jersey Bed Sheet Set costs $150 in king size, compared with $140 for queen and $130 for full size. As for bed frames, Castlery’s bestselling Seb Bed costs $1,099 in king size – $100 more than queen size.

Should I buy a king size mattress?

Sleep is a big part of your life, and buying a great mattress in the right size for you and your partner can significantly improve sleep quality. King size mattresses do cost more than full and queen size options, but if you’re already spending more than $1,000 on a mattress that you’ll be sleeping on for years, it pays to get the best one you can afford.

Not only does the 6ft 4in width of a king size mattress deliver plenty of space to sprawl out sideways while you sleep, it also enables the air to circulate in and around when the night is warm. Your kids and pets will be able to join you for cuddles, and the whole family can take naps together.

Let’s not forget that the abundant sleeping surface of a king size mattress means it has a large footprint, too, so you’ll need plenty of space in your home and bedroom to accommodate it. Note, too, that when it’s time to change the sheets, you’ll be wrestling with a mattress that weighs as much as an adult – but once you’re done, you can sleep it off in king size style and comfort.