Why Is My Mattress Hanging Over the Base?

Applies to: Sleep Number mattresses and compatible bases. Some steps apply only to mattresses with a Sleep Number® setting or FlexFit® adjustable bases.

If your mattress hangs over the base, looks crooked or feels uneven, start by checking its alignment and support. Then follow the steps for your mattress type. If your mattress has a Sleep Number® setting, you will also check the air chambers, hoses and setting.

Quick answer

A mattress may hang over the base if it is not centered, the base is narrower than the mattress, or the cover, foam or inner materials have shifted. A slight curve at the edge may be normal. If the mattress hangs over by more than about 1 inch, slides or feels unsupported, check the alignment, base size, cover and inner materials. If your mattress has a Sleep Number® setting, also check its setting and hose connections.

Choose the problem you see

• The mattress hangs over the side or foot: Check alignment, base size, the cover and inner materials.
• The mattress looks crooked or shifted: Check whether the mattress or materials inside the cover have moved.
• The edge feels soft or unsupported: Check the foam, cover fit and edge support.
• One side is lower or will not fill on a mattress with a Sleep Number® setting: Check the Sleep Number® setting, air level and hose connections.

Before you begin

Remove all bedding and make sure no one is in bed. If your mattress has Sleep Number® setting, set each side to 100 and wait a few minutes for it to fill. If your mattress does not have a Sleep Number® setting, skip that step. Smooth the top and sides with your hands so you can see the mattress shape.

1. Check the mattress alignment

• Stand at the foot of the bed and check whether the mattress is centered on the base.
• Compare the overhang on both sides and at the foot. A mattress should not hang several inches beyond the base.
• If it is crooked, ask another adult to help re-center it.
• If it moves out of place again, check the cover, inner materials, attachment points and base.

2. How to measure your mattress and base

Measure the mattress and base at the head, middle and foot. Measure from side to side at the widest point. Ask another adult to help if needed.

• Write down all mattress and base measurements.
• Compare the head, middle and foot measurements.
• If one part of the mattress is much wider, bowed or stretched, the cover, foam or inner materials may have moved or lost shape.
• If the mattress is more than about 1 inch wider than a FlexFit® adjustable base, or hangs over the base by several inches, continue with the steps below. Contact Customer Support if the mattress still does not fit correctly after troubleshooting.

3. Check the cover and inner materials

• If your mattress cover is designed to open, unzip it carefully. Do not open a cover that is not made to be removed.
• Check that the foam and other inner materials are flat, centered and not folded.
• If your mattress has a Sleep Number® setting, also check that each air chamber is flat and centered.
• Gently move shifted materials back into place. Do not force or pull parts.
• If foam is torn, compressed or no longer holds its shape, contact Customer Support.

4. If your mattress has a Sleep Number® setting

• Set each side to a Sleep Number® setting of 100 and wait a few minutes.
• Check that the hoses are secure and are not pinched, bent, loose or trapped under the mattress.
• If a side fills and then loses air, contact Customer Support for help checking for air loss.
• If you cannot safely disconnect a hose, do not force it.

5. If you have a FlexFit® adjustable base

A FlexFit® adjustable base is usually about 1 inch narrower than the mattress so it can fit inside a standard bed frame. If the mattress hangs over by more than about 1 inch, hangs over the foot, slides when the base moves or stays crooked after re-centering, check the attachment points and see Mattress Sliding on Base.

If your mattress uses magnets, straps, clips or other attachment points, make sure they line up and are secure. If the cover is stretched or the attachments will not stay in place, contact Customer Support.

When to contact Customer Support

• The mattress still hangs over after you re-center it.
• It hangs over the side or foot by several inches.
• The mattress feels unstable or unsafe.
• Foam, the cover, magnets, straps or attachment points are torn, stretched, missing or out of place.
• If your mattress has a Sleep Number® setting, one side will not fill, loses air or stays much softer than the other.
• You need help with parts, warranty coverage or service options.

Frequently asked questions