Knee Pillows for Side Sleepers

What a knee pillow actually does

Its job is to restore the width your legs lose when they stack. By holding your knees roughly hip-width apart, the pillow keeps the top hip from dropping forward, which keeps your pelvis square and your lumbar spine neutral. It also stops bone-on-bone contact between the knees and ankles, and it takes tension off the iliotibial band running down the outside of your thigh.

• Lower back — removes the rotational twist that causes morning stiffness.
• Hips — levels the pelvis and reduces pressure on the greater trochanter (the sore point on the outside of the hip).
• Knees and ankles — prevents the pressure and skin irritation of joints pressing together.
• Sciatic symptoms — often eases nerve irritation aggravated by a twisted pelvis, though it is not a treatment for the underlying cause.
• Pregnancy — the main reason a knee or wedge pillow is recommended for left-side sleeping in the second and third trimester.

Which shape to choose

There are four common formats and they suit different sleepers.

• Hourglass memory foam — the standard. Cinched waist holds it in position between the knees. Best all-round pick.
• Half-moon / wedge — thinner; can also go under the knees for back sleeping. Good if a full knee pillow feels too wide.
• Strapped knee pillow — has a leg strap so it cannot escape when you turn. Worth it if you move a lot, though the strap bothers some sleepers.
• Full-length body pillow — supports knees, hips and top arm at once. Best for pregnancy, shoulder pain and restless sleepers, but it takes up half the bed.

Loft and firmness

The right thickness is the one that keeps your knees roughly as far apart as your hips are wide — for most adults that is 5 to 7 inches of pillow. Too thin and the top hip still drops; too thick and you push the top leg up past neutral, which creates a new twist in the opposite direction.

Firmness should be medium to firm. A soft knee pillow compresses to nothing within an hour under the weight of a leg, which is why cheap polyester versions stop working after a couple of weeks. High-density memory foam or latex holds up.

Where to put it

Placement matters more than people expect, and the most common mistake is putting it too high.

• Lie on your side with both knees bent about 30 degrees.
• Place the pillow so it sits between the knees and the lower shin — not up against the thighs.
• Check your hips: the top hip bone should sit directly above the bottom one, not rolled forward.
• Keep your top leg roughly parallel to the bed rather than sliding forward off the pillow.
• For back sleeping, move the same pillow under your knees instead to flatten the lumbar arch.

What it won't fix

A knee pillow addresses rotation. It will not compensate for a mattress that is too firm for your hips, and it will not correct neck or shoulder pain — that is the job of your head pillow's loft. If your lower back still aches after two weeks with a knee pillow, look at mattress pressure relief next, and at whether your head pillow is dropping your upper body out of line.

It also takes a few nights to get used to, and it will migrate out of place at first. If you wake up and it has ended up at the foot of the bed every night, switch to a strapped model or a body pillow.

Pillows we recommend for this

Coop Home Goods Body Pillow

Side sleepers, pregnancy, and hip alignment

8.9Read review

PharMeDoc U-Shaped Pregnancy Pillow

Pregnancy and side sleepers who want full-body support

9.0Read review

Boppy Side Sleeper Pregnancy Pillow

Smaller beds and second- or third-trimester bump support

8.6Read review

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