King vs. Full Size Mattress: What’s the Difference?

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Based on the names alone, both king and full size mattresses sound like they offer an incredibly spacious sleeping area, but this really isn’t the case. A king size mattress is significantly larger than a full size mattress, offering plenty of room for a pair of sleepers. A full size mattress is significantly more affordable, but may not provide enough room for more than a single adult. Let’s take a closer look at these mattress sizes in our side-by-side comparison below. 

What’s a Full Size Mattress? 

Dimensions: 54 inches wide by 75 inches long

Also known as a double mattress, a full size mattress is significantly smaller than a king size bed. Both full and double refer to the same mattress size, and the two terms are used interchangeably. Double is the more antiquated of the two terms, but some manufacturers still use the name to refer to the more popular full size bed. 

The full or double bed was developed around the 1870s, when mattress manufacturers came together to start standardizing their sizes. This standardization eliminated a lot of dimensional discrepancies that occurred between bed makers and mattress manufacturers, and as an added benefit, it made buying sheets, frames, and bedding accessories easier for the consumer. 

Today, full size mattresses are a popular choice for student dormitories and guest rooms, as the full size mattress offers the right amount of space for a single sleeper about the size of a teenager or young adult. Memory foam options are also widely available for this mattress. 

Full Size Mattress Benefits 

Most full size mattresses will be more affordable than the average king size mattress, making them ideal for younger adults or students on a tight budget. Full size mattresses are also fairly lightweight compared to their king size counterparts, and they are easier to move around and relocate than queen size mattresses, kings, and other larger varieties.  

Full Size Mattress Drawbacks 

Despite the name, the full or double size mattress does not comfortably fit two adults. If the bed is shared by a pair of sleepers, they will likely disturb and wake each other when they move around in their sleep. 

With an average length of about 6.25 feet, a full size mattress may not provide enough room for taller sleepers, forcing them to use every available inch of the bed or hang their feet off the foot of the bed.   

What’s a King Size Mattress? 

Dimensions: 76 inches wide by 80 inches long 

The standard king size mattress, otherwise known as the eastern king, is one of the largest bed sizes widely available throughout the marketplace. There are a few offshoots of the standard king size mattress including the California king, Wyoming king, Texas king, and Alaskan king, but finding sheets, comforters, bed frames, and other bedding accessories for these specialty models is much harder than buying for a standard king size mattress. 

The king mattress’s popularity surged in the 1940s and 1950s during the economic boom that followed World War II. The average property owner in the United States was making a higher income than those in previous generations, with many families moving from cities to the suburbs. Suburban homes were more spacious than their metropolitan counterparts, and the increased demand for the king size mattress prompted many manufacturers to include this larger mattress in their product lines.  

King Size Mattress Benefits 

The most popular benefit provided by the king size mattress is the ample and spacious sleeping space provided by the large mattress size. King mattresses offer plenty of room for two adults and even parents who occasionally sleep with their toddlers or young children. Sleepers who tend to toss and turn a lot during the night typically won’t bother their partner either, thanks to the large width and length provided by the king. 

Aesthetically, king size mattresses are ideal for furnishing large, spacious suites and master bedrooms. Because the king is larger than most other standard mattress sizes, the extra width and longer mattress dimensions will help to fill out the empty space and balance out the room—especially if the space lacks a dresser or other bedroom furniture. 

King Size Mattress Drawbacks 

As the more expensive of the two options, the king size mattress carries a heavier price tag than most full size mattresses. 

Due to their larger size and bulkier construction, kings are also harder to move than the smaller full size, so they may not be ideal for people who tend to relocate often or those furnishing a bedroom up several flights of stairs. Narrow stairway landings may also make getting a king size mattress into your bedroom physically impossible, so be sure your building or home has enough space to accommodate the large mattress before you buy one.  

Frequently Asked Questions 

Other than standard, what other king sizes are available?  

There are a few specialty sizes that are offshoots of the standard king and not as widely available, including California king (72 inches wide by 84 inches long). Cal kings are narrower but longer than a standard king. However, there are also Wyoming king (84 inches wide by 84 inches long), Texas king (80 inches wide by 98 inches long), and Alaskan king mattresses (108 inches wide by 108 inches long). 

What’s the difference between a king and a California king bed?  

A less widely available version of the standard king size mattress is the California king size mattress. Measuring 72” wide by 84” long, it’s a bit more narrow than the standard king, but the California king mattresses are longer than standard kings. So, they offer extra length to accommodate tall people and provides more foot room. 

What’s the average price of king and full mattresses?

Full mattresses are the more affordable of the two, with most models ranging from $250 – $2,500, while standard kings range from $600 – $10,000. 

Which option is best for co-sleeping?  

As the longer of the two beds, a king is certainly better than a queen for families who prefer to co-sleep with children. The king is the more spacious of the two options in both width and length. 

Do two twin beds placed side by side equal a king bed?  

No – while the width and length measurements are somewhat close, two twin size mattresses do not equal one king. However, two twin xl mattresses do equal one split king size mattress if they are placed side by side within the same bed frame, so you can create a make-shift bed in the event that you have a split king frame and two twin xl mattresses.  


While king size mattresses offer plenty of room for couples and are ideal for furnishing larger bedrooms, full and double size mattresses are better suited for children, teenagers, and students living in college dorm rooms. Full mattresses provide the more affordable option, and they’re easier to move and carry up and down a flight of stairs. Before you buy a king or full size mattress, consider your budget, your bedroom size, and your own personal preference to ensure you make the right decision.   

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