How large should your mattress be? The obvious answer is, “The right size to fit your bed,” but that begs another question: how big should your bed be? Of course size isn’t the only mattress consideration – there’s also firmness, construction (foam, springs or hybrid) and features such as cooling ability, antimicrobial treatment and contouring. Still, for most people, the first decision is what size to choose.

When consulting a mattress size guide, don’t forget that size is more than just length and width. Thickness, or depth, is a dimension as well. The ideal thickness of your mattress depends on factors such as body shape, sleep position and what kind of bed it’s to be paired with.

Choosing the Right SIze

A mattress must be big enough to accommodate the person or people who will be using it and small enough not to overcrowd its room. This mattress size and dimensions guide shows the length and width of the six common mattresses and the size of the smallest room that won’t feel crowded when the bed is in place. Please note that mattress dimensions are not exact. They may vary from manufacturer to manufacturer by as much as two inches.

A rule of thumb says a mattress should be at least five inches longer than the person is tall. However, the size of the sleeper isn’t the only factor. Some people lie down neatly and never move until morning. Others sprawl and flop all night long. The latter will prefer to have more width and perhaps a little more length as well.

In some families, children, cats and dogs tend to find their way into the master bed during the nighttime hours. These folks might find that some extra bed surface ensures happiness for two-legged and four-legged “people” alike.

The issue becomes more complex when buying a mattress for a sleeper who won’t stay the same size. A twin mattress is right for most children, but if they surprise you with a growth spurt during their teen years, they might be well served by the extra inches of a twin XL. A queen bed may even work best for a child if you have the space. You have to think about how long you expect the mattress to last. A typical mattress lifespan is eight to 10 years.

There’s also the question of what goes into a guest room. A full mattress will accommodate singles and couples who don’t mind being close, but some pairs will prefer a queen. A matching set of twin XL’s is a flexible solution; they can be moved together or apart depending on the situation.

Here are some advantages of each common size:

Crib/Toddler Mattresses

Crib mattresses are federally mandated to be 27 by 52 inches. That’s so they’ll fit snugly in a standard crib. Still, you should check the fit when you drop the mattress in. If you can put more than two fingers between the crib and the mattress, the gap is too large.

A toddler mattress is the same size. If you have a toddler bed, or a crib that converts into one, you can keep the same mattress. A crib mattress must be firm as a safety measure, while a toddler mattress can have some give. There are convertible mattresses with crib firmness on one side and toddler firmness on the other.

Twin Mattresses

At about 39 by 75 inches, a twin mattress is suitable for most people up to around 5’10”. It will fit kids all through childhood if they don’t grow too much as teens. It also accommodates adults who are average height or less. You might also deploy it in a small or irregularly shaped guest room.

A twin mattress will most often be the right choice for bunk beds and daybeds.

Twin XL

The XL stands for extra long. At around 39 by 80 inches, a twin XL is typically five inches longer than a twin, the same length as a queen or king. This makes it the mattress of choice for a king size split adjustable bed. According to the 5-inch rule, it will comfortably suit anyone up to about 6’3”.

Like twins, twin XL’s can be appropriate for small or irregular rooms. They’re also a preferred size for dorm rooms, which often accommodate tall people in tight quarters. Twin mattresses are a good option for many first apartments, as they take up less space than a queen or king mattress.

Many single sleepers will prefer a twin XL even if they’re not too tall for a twin. However, this mattress may not be wide enough for a restless sleeper or one who welcomes Fluffy or Fido into the sack. These might be better served by a full or a queen.

There can be limited bedding choices for twin XL. A regular twin blanket or flat sheet will work OK, but a mattress pad or fitted sheet must be specifically made to accommodate the extra length.

Full Mattress

A full mattress is sometimes called a double. At approximately 54 by 75 inches, it’s the same length as a standard twin but about 15 inches wider. The full can be a good option for single sleepers who like to sprawl. Some parents will choose a full for an older child.

A full mattress can be adequate for couples who don’t have room for a larger bed. It probably won’t suffice for tall single sleepers or for couples who toss and turn. Many people select a full mattress for a guest room that isn’t large enough to accommodate a queen. It’s also a popular choice for cabins and vacation homes.

Queen

The queen mattress size is typically 60 by 80 inches, and queen is the most popular mattress choice. It's large enough to suit almost all couples and small enough to fit comfortably in a master bedroom as well as quite a few smaller bedrooms. A typical master bedroom looks orderly and uncrowded with a queen bed, a dresser, a chest, a couple nightstands and even a desk.

Because it’s so well-liked by couples, a queen is an appreciated amenity in a guest room. Even those without bedmates enjoy the spacious dimensions. Its popularity ensures that a large selection of bedding and accessories will always be available at reasonable prices.

King

While the queen mattress is adequate for most people, the king mattress size, about 76 by 80 inches, provides a luxurious roominess that some folks just won’t live without. Two people can toss, sprawl and roll all night and never feel constricted. In a bedroom large enough to harbor it, a king bed, especially one with a stylish headboard, makes a fashion statement that distinguishes the space.

Compared to a queen, the additional 15 inches of width delivers plenty of space for extra bedmates that appear during the night, whether they be children or the family pets.

California King

Measuring around 72 x 84 inches, the California king is about four inches longer than a king but also four inches less wide. There aren’t many people too tall to sleep comfortably in a California king. Beside accommodating the vertically gifted, these mattresses are sometimes found in rooms with odd or narrow dimensions. Also, Cali king mattresses are often used in adjustable beds.

Length and Width Aren’t Everything

When you place your new mattress on your bed, you also have to provide bedding. Bedding is available for all the sizes, but with twin XL, full and California king, the selection may not be as varied, as cost-effective or available in as many places. You can make do with blankets, spreads and flat sheets made for similar sizes (e.g., king bedding for a California king), but fitted sheets and mattress covers have to be exactly right.

How Thick Should a Mattress Be?

There’s no standard thickness for each mattress size. The right depth depends on preferred height from floor, sleeper mobility, body weight and sleeping position. In general, thicker mattresses are more luxurious and thinner ones more budget-friendly. However, that doesn't mean that thicker is necessarily better.

Thicknesses as categorized as follows:

• Low, 2-5 inches. Children are usually comfortable on these, and they go well with bunk beds and trundle beds.

• Slim, 5-10 inches. Besides being good for children, they’re often preferred by adults who struggle getting in and out of a higher bed.

• Standard, 10-12 inches. These are thick enough to have a comfort system and a durable support core. Most back sleepers find them comfortable.

• Thick/deep, 12-14 inches. Thick mattresses have more substantial comfort systems and cores. They’re often preferred by side sleepers as well as heavier back sleepers.

• Extra thick/deep, 14+ inches. These work for heavy sleepers and side sleepers who need extra pressure relief.

If your mattress is an ideal thickness, the bed will be comfortable for sleeping and easy to get in and out of. In general, your feet should rest flat on the floor when you sit on the edge. Remember that some but not all mattresses require box springs.