King Size Memory Foam Mattress

By April Mayer
Last Updated On March 8th, 2021

Over the last 20 years, memory foam has become a popular mattress material. This foam responds immediately to pressure and contours closely to the body, helping your muscles fully relax…

King Size Memory Foam Mattress

Over the last 20 years, memory foam has become a popular mattress material. This foam responds immediately to pressure and contours closely to the body, helping your muscles fully relax so you can get deeper, more restful sleep. Memory foam beds are particularly helpful for those with chronic pain or sleep disorders.

While queen size memory foam mattresses are one of the most popular choices among Americans, most couples prefer a king size mattress. Sixteen inches wider than a queen, king size beds give each sleeper 38 inches of personal space.

Best Mattresses At
Better Prices

Save Hundreds On Sleep

Shop Our Mattresses

This additional width is perfect for those who frequently toss and turn, couples who need more room to spread out, and families who prefer to co-sleep. The 80-inch length of a king size mattress is also ideal for taller couples who need more legroom to get comfortable.

With the popularity of memory foam, many different varieties have entered the market. However, not all memory foam is manufactured the same way, which affects the durability, firmness, and breathability of the mattress.

To help you shop for a new mattress to keep you comfortable and supported for many years, we outline some of the best king size memory foam mattresses on the market.

Best King Size Memory Foam Mattresses

At Amerisleep, each of our memory foam mattresses is designed with a specific sleep position and body type in mind. For example, the AS2, our medium-firm mattress, works well for back sleepers and heavier individuals who need to avoid excess sinking. However, our medium-soft mattress, the AS4, is perfect for petite side sleepers.

Every Amerisleep mattress also comes with a 100-night sleep trial and a generous 20-year warranty. Each foam layer of our beds is also certified by CertiPUR-US®, guaranteeing it is free of toxic chemicals and has minimal VOC off-gassing (Volatile Organic Compounds) when brought into your home.

Below, we outline each of our king memory foam mattresses and explain why they might be right for you.

Amerisleep AS1: King Size Memory Foam Mattress

Mattress Depth: 10 inches (25.4 cm)

Price of a queen size: $1119

The AS1 is our firmest model, designed for stomach sleepers and back sleepers who prefer a firm feel. With a 10-inch thickness, the AS1 has very little give, so the hips and shoulders do not sink into the bed but remain lifted on the surface. This firmness reduces the pressure on the spine, so stomach and back sleepers wake with less pain.

The comfort layer on the AS1 is made with our Bio-Pur® plant-based memory foam, which retains less heat and moisture than traditional memory foam varieties. This breathable foam, combined with our soft, ventilated cover, keeps the surface of the AS1 cool and inviting.

The base of the AS1 is an 8-inch layer of our Bio-Core® foam, a study support foam designed to keep body weight evenly distributed and prevent sagging. This stable base ensures the mattress remains supportive throughout its lifespan.

Product Highlights:

  • 2-inch Bio-Pur® layer offers some cushion
  • Firm Bio-Core® provides sturdy support

Shop AS1

Amerisleep AS2: King Size Memory Foam Mattress

Amerisleep AS3 is the best mattress of 2019

Mattress Depth: 12 inches (30.5 cm)

Price of a queen size: $1259

The AS2 is our medium-firm mattress, recommended for back sleepers and heavier sleepers over 230 pounds. The 2-inch Bio-Pur® top layer of the AS2 is firm enough to keep the hips aligned with the shoulders to prevent spinal misalignment.

The responsiveness and conformity of the Bio-Pur® foam allows it to mold to the curves of the body to prevent pressure points. This combination helps sleepers wake with less joint pain and muscle stiffness.

The 2-inch transition layer of the AS2 features our Affinity foam with HIVE® technology. Hexagonal cutouts along the foam’s surface are balanced to cushion and protect sensitive areas and provide more support to the lumbar spine—promoting a healthy, comfortable sleep position.

The 8-inch Bio-Core® foam in the base of the AS2 supports both these layers of foam and prevents premature sagging and indentations.

Product Highlights:

  • Bio-Pur® is contouring and pressure-relieving
  • Affinity with HIVE® promotes airflow and encourages better sleep postures
  • Bio-Core® prevents premature wear and tear

Shop AS2

Amerisleep AS3: King Size Memory Foam Mattress

best mattress on amazon

Mattress Depth: 12 inches (30.5 cm)

Price of a queen size: $1329

The AS3 is our most popular mattress since it has a medium firmness—the perfect balance of cushioning and support. The 3-inch Bio-Pur® comfort layer is soft enough to cushion the body’s curves and alleviate pressure points. However, this foam’s slight firmness also keeps the hips and shoulders from sinking too far into the mattress and forcing the spine to bow.

The medium firmness of the AS3 makes it a great option for combination sleepers and those who tend to toss and turn during sleep. The AS3 is also a great compromise for couples with different body types and sleep positions.

The AS3 has a 2-inch Affinity foam transition layer with HIVE® technology. Hexagonal cutouts near the hip and shoulder joints are spaced further apart to offer more compression and contouring. However, along the back, cutouts are closer together and firmer to support the lumbar spine.

The 7-inch Bio-Core® base layer in the AS3 ensures even weight distribution and guards against structural damage that could change the mattress’s support.

Product Highlights:

  • Bio-Pur® relieves soreness, aches, and pains
  • Affinity with HIVE® keeps you lifted while providing zoned support
  • Bio-Core® reinforces Affinity and Bio-Pur®

Shop AS3

Amerisleep AS4: King Size Memory Foam Mattress

best gel memory foam mattress

Mattress Depth: 12 inches (30.5 cm)

Price of a queen size: $1469

The AS4, our medium-soft mattress, is recommended for average weight side sleepers. Like the AS3, the AS4 also has a 12-inch thickness. However, instead of a 3-inch comfort layer, the AS4 has 4 inches of conforming yet breathable Bio-Pur® memory foam. This thick comfort layer offers sleepers more compression, ensuring the joints remain cushioned when side sleeping.

Although this mattress is on the soft side, the 1-inch Affinity foam layer with HIVE® technology ensures the heaviest parts of the body don’t sink too far into the mattress and lead to muscle tension. The HIVE® cutouts gently lift the hips to keep the spine aligned.

Like all Amerisleep mattresses, the stable Bio-Core® base reinforces support and guarantees the life of your mattress by reducing premature sags and indents.

Product Highlights:

  • Bio-Pur® offers thick, cloud-like cushion
  • Affinity with HIVE® keeps you lifted
  • Bio-Core® offers long-lasting support

Shop AS4

Amerisleep AS5: King Size Memory Foam Mattress

Mattress Depth: 14 inches (35.6 cm)

Price of a queen size: $1749

The AS5 is our most luxurious mattress because it contains a blend of ultra-soft, contouring Bio-Pur® with bouncy and adaptable Active Flex. Side sleepers who like a lot of cushion sleep well on this mattress because it offers maximum comfort around the joints to alleviate muscle tension.

The supportive Active Flex transition layer also makes the AS5 suitable for heavier sleepers who prefer a softer mattress. Thanks to this 2-inch response foam, the hips and shoulders remain lifted and aligned throughout the night.

Unlike most soft mattresses, heavier sleepers do not experience over-sinking, or the uncomfortable sensation of feeling “stuck” in the mattress, on the AS5. Beneath this layer, our Affinity Foam with HIVE® reinforces the Active Flex layer and promotes a neutral spine for deeper sleep and less pain in the morning.

At the base of the AS5 is 7-inches of our Bio-Core® foam to keep body weight evenly supported and reduce structural defects.

Product Highlights:

  • Comfort layer of Bio-Pur® relieves pain-causing pressure points
  • Active Flex layer gives the bed some bounce
  • Affinity with HIVE® offers zoned support
  • Bio-Core® deters sagging

Shop AS5

Who Should Choose A King Size Mattress?

King size mattress dimensions are 76 inches wide by 80 inches long, offering couples 38 inches of space on each side of the bed. While king size beds are one of the most expensive mattress sizes and require a larger bedroom, they come with many great benefits.

The following individuals may find a better night’s sleep on a king size mattress.

  • Couples who Prefer More Room: Couples who tend to toss and turn or change positions frequently during sleep experience less motion transfer on a king size bed. Additionally, couples with different sleep schedules may benefit from a king because they can get in and out of bed without waking their partner.
  • Larger Couples: If one or both individuals are 230 pounds or more, a king size bed gives each sleeper more elbow room and space to get comfortable.
  • Taller Couples: Couples where one or both of the sleepers are 6 feet tall (72 inches) should consider a king size bed. The length of a king gives tall individuals more legroom without worrying about their feet dangling off the end of the mattress. However, for couples taller than 6 feet, a California king mattress may be a better choice. Cal kings are 84 inches long—4 inches longer than a standard king size bed.
  • Families Who Co-Sleep: Couples who prefer to co-sleep with their children often find a king size mattress more accommodating than a queen size. With 76 inches in width, both parents and children can spread out comfortably without feeling cramped.
  • Those With a Large Bedroom: To accommodate a king size bed, your bedroom should be at least 12 feet by 12 feet. This size bedroom fits a king size bed and leaves plenty of room around the bed’s perimeter for additional furniture, such as nightstands.

Why Choose a Memory Foam Mattress?

While there are many mattress types available in king size dimensions, memory foam beds offer several advantages. Below, we outline some of the benefits of a memory foam bed and other important factors to consider when choosing a new mattress.

Cooling Features

The biggest complaint regarding memory foam is that it tends to retain heat and moisture. However, many brands have come up with unique manufacturing methods to combat this issue.

King Size Memory Foam Mattress

The best memory foam mattresses come with cooling features such as plant-based foam, gel infusions, or mineral infusions, such as copper and graphite. In most cases, breathable memory foam lasts longer than traditional memory foam varieties because, with less heat retention, the foam does not deteriorate as quickly.

At Amerisleep, we construct our Bio-Pur® comfort foam with plant-based oils, rather than 100 percent petroleum-based oils. With fewer synthetic oils, Bio-Pur® doesn’t hold on to body heat, keeping the bed’s surface cool and comfortable.


Memory foam mattresses are available in several different firmness levels, so they can accommodate a wide variety of sleepers.

Sleep Position

Mattresses for side sleepers are often soft to medium for maximum comfort and pressure relief. However, the best mattresses for back sleepers are medium to medium-firm to prevent excess sinking and spinal misalignment.

We don’t recommend stomach sleeping since this position can cause chronic neck and back pain. However, if you find it difficult to avoid this position, mattresses for stomach sleepers should be extra firm to keep the hips and shoulders lifted and aligned.

The best mattresses for couples with different firmness needs are medium. Medium mattresses are soft enough to prevent pressure points when side sleeping and firm enough to reduce sinking when back sleeping.

Body Type

Your body type can help determine the right mattress firmness for you. Lightweight sleepers (130 pounds or less) tend to sink very little, so they need a soft bed to experience deep contouring and pressure relief. In most cases, the right mattresses for lightweight sleepers are soft to medium. A firmer mattress could cause pressure points to form near the hip and shoulder joints.

Heavier individuals (230 pounds or more) typically sink more. If they rest on a mattress that is too soft and offers little support, they may sink too much. Over sinking could cause the spine to bow and lead to pressure and tension build up in the lower back. Therefore, they need a firmer mattress to keep the hips and shoulders lifted and aligned throughout the night.

The best mattresses for heavier individuals are often medium-firm. Heavy sleepers who prefer a soft mattress should choose one with a supportive response layer designed to prevent excess sinking and spinal misalignment.

Motion Isolation

A memory foam mattress with a stable foam base offers minimal motion transfer. For light sleepers or couples with different sleep schedules, less motion transfer means fewer sleep disruptions and a better night’s sleep.

Pressure Relief

Memory foam is highly responsive, so it contours closely to the body’s curves, ensuring you are cushioned and protected from pressure points. For those with chronic pain, the pressure relief of a memory foam mattress can promote healing and deeper, more restful sleep.

Frequently Asked Questions

Is a memory foam mattress good for back pain?

Yes, memory foam mattresses contour closely to the body to ensure each area is cushioned and supported. The best memory foam mattresses for back pain are those with a medium to medium firm feel. With a slight firmness, the hips and shoulders stay aligned so the spine can remain neutral. With the spine in a neutral position, the back muscles can fully relax and recover during sleep.

Which is better, memory foam or gel memory foam?

Traditional memory foam tends to trap warm air, which can cause the mattress to heat up and lead to uncomfortable night sweats. However, gel memory foam mattresses are infused with cooling gel beads that absorb body heat throughout the night and pull it away from the bed’s surface.

If you are a hot sleeper, a gel memory foam bed or a memory foam mattress infused with plant-based oils provides a cooler night’s sleep.

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

A standard king size mattress measures 76 inches wide by 80 inches long. California king mattresses measure 72 inches wide by 80 inches long, making them 4 inches longer than a standard king mattress. If you are taller than 6 feet (72 inches), you may prefer a California king since it offers more legroom and space to get comfortable.

Is a split king two twin mattresses?

No. Two standard twin mattresses do not equal a king. However, two twin XL mattresses, each measuring 38 inches wide by 80 inches long, equal one king size mattress. Many mattress companies offer a split king option, allowing couples to choose a different firmness on each side of the bed.

Is there a bed bigger than California king?

There are three mattresses bigger than a California king—a Wyoming, Texas, and Alaskan King. While these beds are not widely available, they can be found at some specialty retailers. These larger mattresses have the following dimensions:

  • Wyoming King: 84 inches wide by 84 inches long
  • Texas King: 80 inches wide by 98 inches long
  • Alaskan King: 108 inches wide by 108 inches long


If you are interested in a new king size bed, you can’t go wrong with a high-quality memory foam mattress. These beds provide deep contouring and pressure relief, so you can get a good night’s sleep and wake feeling refreshed. Plus, a luxurious king size bed gives you and your partner plenty of room to stretch out and find the best sleep position for your needs.

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

About the author

April Mayer has a degree in exercise physiology and is a firm believer in the power of a good night’s sleep. April’s passion lies in helping others lead more productive lives by helping them get sound, restful sleep every night. April primarily writes about foods and vitamins for better sleep and has written several “better sleep guides” covering a wide variety of topics in her time with Early Bird.

View all posts

Discover the ultimate sleep system

Choose your mattress

Shop top-rated mattresses with proven sleep-boosting materials.

Browse Mattresses

Get a pillow

We have the perfect pillow to pair with your mattress.

Browse Pillows

Pick out bedding

Bring out the best in your mattress with our soft and breathable bedding.

Browse Bedding