Under knee pillow: the simple back sleeper support, and when not to use it
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- Knee wedge with flat top. Best for: Back sleepers who want steady support all night. See options on Amazon
- Half-moon bolster. Best for: A modest lift that stays put. See options on Amazon
- Round foam bolster. Best for: Travel or light support. See options on Amazon
- Lumbar roll or small rolled towel. Best for: Back sleepers who still feel a gap at the waist. See options on Amazon
Why a pillow under the knees helps back sleepers
Mayo Clinic's advice for back sleepers with back pain is to place a pillow under the knees, and to add a small rolled towel under the waist if you need more support. The Sleep Foundation agrees, noting you can use a pillow, a rolled-up towel, or a wedge pillow for the same effect. Its knee pillow guide adds that back sleepers can place a pillow under their knees to relieve lower back tension.
The idea is to take the stretch off the front of the hips. With the knees slightly bent, the pelvis can tilt into a more relaxed position.
Bolster, half-moon or wedge?
| Type | Support | Best for | Trade-off |
|---|---|---|---|
| Round bolster | Small, focused lift behind the knees | Light support, travel, massage-table style | Can roll away; pressure on one strip of the leg |
| Half-moon bolster | Flat bottom, rounded top | Staying put on the mattress | Limited height |
| Knee wedge (thigh ramp plus flat top) | Supports thighs and calves | All-night use and broader contact | Bulkier; takes more bed length |
| Folded bed pillow | Variable | Trying the idea first | Flattens and shifts during the night |
If your main goal is raising the legs above the heart for swelling, that is a different job. See our leg wedge pillow guide.
Choosing the right height
- Start low. You want a slight knee bend, not a sharp one. A support that is too tall can tilt the pelvis the other way.
- Check your lower back. When the height is right, the small of your back should rest closer to the mattress without effort.
- Support the calf, not just the knee. A narrow roll under the joint alone can feel like a pressure bar by morning.
- Firm enough to hold shape. Soft pillows lose height through the night.
- Washable cover. It sits against bare legs every night.
For more on foam types, see our memory foam knee pillow page.
When not to put a pillow under your knee
After knee replacement. Robert Jones and Agnes Hunt Orthopaedic Hospital says to rest with the operated knee straight when lying on your back. It warns that a pillow beneath the knee can tighten the tissues behind it and lead to a fixed bend. This is a different situation from ordinary back pain. Our knee replacement pillow page explains the difference. Always follow your own surgeon's instructions.
Circulation concerns. The Sleep Foundation notes that people with certain circulation issues or medical conditions may need to avoid pressure around the knees. Ask your clinician if that applies to you.
Side sleepers. An under-knee pillow is for back sleeping. On your side, the pillow goes between the knees; see our side sleeper knee pillow guide.
A simple routine to try
- Lie on your back with your usual head pillow.
- Slide the knee support in so it sits under the backs of your thighs and knees, with the calves resting on it or just past it.
- Add a small rolled towel under your waist only if your lower back still feels unsupported, as Mayo Clinic suggests.
- Notice how your back feels in the morning, and adjust height over several nights.
What to look for when you buy
Knee wedge with flat top
Best for: Back sleepers who want steady support all night
The Sleep Foundation says a wedge under the knees can achieve the same effect as a pillow, and the broad top supports thighs and calves rather than one point.
Watch out: Bulkier than a bolster and takes up bed length.
See options on AmazonHalf-moon bolster
Best for: A modest lift that stays put
The flat base resists rolling, giving the slight knee bend Mayo Clinic describes for back sleepers.
Watch out: Fixed height; may be too low for some.
See options on AmazonRound foam bolster
Best for: Travel or light support
Small and easy to pack, it gives a gentle knee bend when you are away from home.
Watch out: Can roll away and concentrates pressure on a narrow strip of leg.
See options on AmazonLumbar roll or small rolled towel
Best for: Back sleepers who still feel a gap at the waist
Mayo Clinic suggests a small rolled towel under the waist for additional support alongside a pillow under the knees.
Watch out: Too thick a roll pushes the back into an arch; keep it small.
See options on AmazonQuestions people ask
- Is it good to sleep with a pillow under your knees?
- For many back sleepers with lower back pain, yes. Mayo Clinic and the Sleep Foundation both suggest it.
- How high should an under knee pillow be?
- High enough for a slight knee bend that lets the lower back relax, and no higher. Start low and adjust.
- Why should you not put a pillow under your knee after surgery?
- After knee replacement, a pillow under the knee can keep it bent and make regaining full straightening harder. The hospital advises keeping the operated knee straight when resting on your back.
- Should side sleepers use an under knee pillow?
- No. Side sleepers usually place a pillow between the knees to keep the hips stacked.
Sources
- Sleeping positions that reduce back pain (mayoclinic.org), Mayo Clinic
- How to Sleep With Lower Back Pain (www.sleepfoundation.org/physical-health/how-to-sleep-with-lower-back-pain), Sleep Foundation
- Sleeping With a Pillow Between Your Knees (www.sleepfoundation.org/best-pillows/sleeping-with-a-pillow-between-your-knees), Sleep Foundation
- Enhanced Recovery Frequently Asked Questions (rjah.nhs.uk), Robert Jones and Agnes Hunt Orthopaedic Hospital NHS Foundation Trust