King Size Mattress Dimensions: How Big Is a King Size Bed?

King Size Mattress Dimensions

Do you want to upgrade your master bedroom with a truly luxurious mattress? Then you might want to consider a king size bed. This spacious bed will offer you plenty of personal space, even if you’re sharing it with a partner.

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A king size mattress is 76 inches wide and 80 inches long. How thick your mattress is can vary—some may be as short as 8 inches, while others may exceed 14 inches.

For a comfortable night’s rest and to ensure that your bed will last for many years, we recommend choosing a mattress at least 10 inches tall.

Your bedroom should be at least 12 feet by 12 feet if you’re thinking about purchasing a king mattress. Don’t forget to account for the extra space of a king size bed frame. A bed frame’s dimensions often add 2 to 5 inches to each side—that may not sound like a lot, but it can be an important consideration when you’re calculating the available space for bedroom furniture and paths for walking.

Other King Sizes

There’s more than just the basic king mattress to consider if you want the best mattress for a master bedroom. You might want to think about a California king, a split king, or even an oversized mattress such as the Alaska king.

California King

Perhaps the most common king variation is the California king size mattress. It’s 4 inches longer than a king, with the tradeoff that it’s also 4 inches narrower—so a California king measures 72 inches by 84 inches. You may also see a California king referred to as a Western king mattress and a standard king referred to as an Eastern king bed.

If you’re over 6 feet tall and looking for a mattress that will let you lie down without bumping into a headboard or footboard, or leaving your feet dangling over the edge, a California king bed might be the perfect choice.

While a California king mattress costs about as much as a standard king would, related accessories for a California king may cost more than bedding and bed frames for a regular king. If you want to learn more about the pros and cons of each, you can read our king vs. California king guide.

Split King

A split king mattress has the same dimensions as a standard king, with one difference—a split king bed is divided in half. You can check out our split king vs. king guide if you’re interested in reading more about the differences between the two.

This division can improve the bed’s comfort if you share it with a partner. Each half can be customized to one partner’s preferred firmness. A split king mattress might also be the better choice if you plan on pairing it with an adjustable bed.

When you place a split king on an adjustable frame, each half can be moved independently. A standard king mattress can only be adjusted as a whole. Plus, you can save significantly with an adjustable bed and mattress combo.

Oversized Beds

Mattresses larger than a king mattress are not common, but they are available if you go looking for one. Most likely, you’ll have to place a special order for a larger bed size with an online mattress seller.

When it comes to choosing a supersized mattress, popular bed sizes include the Texas king, the Wyoming king, and the Alaskan king.

Size NameMattress Dimensions
Texas king80 inches by 98 inches
Wyoming king84 inches by 84 inches
Alaska king108 inches by 108 inches

We cannot recommend these beds for any room smaller than 12 feet by 12 feet. We would advise against an Alaskan king if your bedroom is smaller than 16 feet by 16 feet.

More Mattress Sizes

A king size mattress isn’t the right choice for everyone. Maybe you have a smaller bedroom, or you don’t have the funds right now for a larger bed. There are four more mattress sizes you can consider.


Size: 38 inches by 75 inches

twin size mattressA twin size mattress is the smallest standard size available, not counting crib mattresses. It’s often used as a child’s first real mattress after their crib or toddler bed, but single adults may want one if they have limited space.

A twin mattress can fit in most bedrooms, and if you’re short on floor space, you may want to consider a lofted bed frame. It’s like a bunk bed, only instead of a bottom bunk, you can put a desk or dresser there.

Twin XL

Size: 38 inches by 80 inches

A twin XL size mattress is 5 inches longer than a standard twin bed, so it can  accommodate a broader range of single sleepers. Dorm rooms often contain twin XL mattresses because they provide a bed suitable for most young adults.

If you’re looking for a smaller mattress for a guest room, a twin XL bed is an excellent choice.


Size: 54 inches by 75 inches

A full size mattress, which is occasionally called a double bed, is 16 inches wider than either type of twin mattress. A full size mattress is an excellent choice if you’re a single sleeper looking for a mattress large enough to sprawl on, yet small enough to fit in most bedrooms and budgets. But if you’re looking for a mattress to share, we have to recommend you pass on a full size bed and consider a queen or larger.

If you’re a tall individual, you might want to look for a full XL size mattress. Like the twin XL and the standard twin, a full XL mattress is 5 inches longer than a standard full size mattress—no more cold toes from having your feet dangle over the foot of the bed.


Size: 60 inches by 80 inches

Queen size mattresses are the most popular choice when it comes to picking a bed size. They are large enough to accommodate two people but small enough to fit in the average bedroom.

If the dimensions of a queen size mattress aren’t quite large enough for your needs, but you don’t want a bed as large as a king, there are a couple of variations you can consider.

There’s the California queen mattress, which like the California king, is 4 inches longer than a standard queen size. It’s a good mattress for tall sleepers who need extra legroom. Unlike the California king, a California queen is the same width as a regular queen.

There’s also the Olympic queen bed, a model that’s 6 inches wider than a standard queen but 10 inches narrower than a standard king. A bed this size can give couples just a little more wiggle room without taking up too much square footage in the bedroom.

Are you unsure whether a queen or a king size mattress is the right choice for your master bedroom? You might find the decision easier after you read our king vs. queen comparison guide.

Frequently Asked Questions

Do 2 full beds make a king?

No. Two full beds pushed together would measure 108 inches by 75 inches. A standard king size mattress is 76 inches by 80 inches. It’s two twin XL mattresses (each one 38 inches by 80 inches) that equal the dimensions of a king size bed.

What is the longest bed you can buy?

When it comes to the standard mattress sizes, a California king size mattress is the longest one. It’s 84 inches, or 7 feet, long. Larger sizes exist, but since they are not standard sizes, you will have a harder time finding them, along with matching bedding and frames.

Is there a bed bigger than a king?

Yes, there are several “oversized” options such as the Alaskan king, Texas king, and Wyoming king.

  • A Texas king, also known as a super king, measures 80 inches by 98 inches.
  • A Wyoming king is 84 inches by 84 inches or 7 feet by 7 feet.
  • An Alberta king is 96 inches by 96 inches or 8 feet by 8 feet.
  • An Alaskan king is 108 inches by 108 inches or 9 feet on all sides.

Since these sizes are nonstandard, you may have to custom order them from an online mattress seller. You should also make sure your bedroom is large enough to accommodate a plus-size mattress.

What is the difference between a split king and a California king?

While both are variations of a standard king mattress, a split king and a California king have different dimensions. A split king is divided into halves that equal 76 inches by 84 inches—allowing two people to sleep on their preferred firmness. A California king is 4 inches and 4 inches narrower than a standard king mattress, making it an excellent choice for sleepers who are taller than 6 feet.

If you’re interested in both, you might want to consider looking for a split California king mattress. They are rare and will require specialized bedding, but if you plan on sharing with a partner, it might be the best way for the two of you to get a comfortable night’s rest.

Will a king size bed fit in a 10 x 10 room?

Technically speaking, yes. A king mattress is roughly 6 ⅓ feet by 6 ⅔ feet, so it will fit in a bedroom that measures 10 feet by 10 feet.

However, we can’t recommend this setup since it will leave little room for anything else in your bedroom. You might be able to squeeze in a couple of nightstands with a dresser and still have enough room to walk around, but the room is likely to feel cramped if you do. And a bedroom that feels cramped hardly promotes a relaxing sleep environment.

This is why we only recommend king mattresses for rooms that are at least 12 feet by 12 feet.

Did We Help?

If you want a bed to share, and that will be the perfect fit in any large master bedroom, you can try a king size mattress. You and a partner can stretch out without bumping into each other during the night. Just make sure you have the space needed for a proper king bed.

This article is for informational purposes and should not replace advice from your doctor or other medical professional.

Sarah Anderson, Certified Sleep Science Coach Sarah Anderson

Sarah Anderson is a sleep, health, and wellness writer and product reviewer. She has written articles on changing and improving your sleep schedule, choosing the right mattress for chronic pain conditions, and finding the best pillow for you. Sarah Anderson has her Bachelor of Arts degree from Arizona State University in Journalism and Mass Communications. Prior to working for Zoma, she wrote for a variety of news publications. Sarah's work has been featured on Bustle, PureWow, and other publications.

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