My Mattress Hangs Over My Base

Applies to: Traditional Sleep Number mattresses and FlexFit adjustable bases.

If your mattress hangs over the base, looks crooked, bows at the sides, or one side feels lower than the other, use this guide to check whether the issue is normal edge shape, mattress alignment, shifted foam, air loss, or a stretched cover.

Quick Answer

A small curve along the mattress edge can be normal because the mattress is made with fabric and foam. If the mattress hangs over the base by more than about 1 inch, looks uneven from side to side, hangs over the foot, feels like it is sliding, or one side will not inflate, continue with the checks below.

Start Here: Match Your Issue

• Mattress hangs over the side or foot: Check alignment, base width, and cover stretch.
• One side is higher, lower, or will not inflate: Check air level, hose connections, and whether the mattress is losing air.
• Mattress looks crooked or shifted: Check whether the foam, air chamber, or internal layers moved inside the cover.
• Edge feels soft or like you may roll off: Check foam rails, cover fit, and whether the side is losing support.
• You cannot safely move or lift the mattress: Ask another person for help or contact support for service options.

Before You Begin

Remove all bedding. Set both sides of the bed to 100 while no one is in bed. Wait a few minutes for the mattress to fill, then smooth the top and sides with your hands.

If the mattress is heavy, hard to move, or attached with strong magnets, do not force it. Get help before lifting, pulling, or trying to re-center it.

1. Check Mattress Alignment

• Stand at the foot of the bed and check whether the mattress is centered on the base.
• Look at both sides and the foot of the bed. The mattress should not hang several inches over the base.
• If the mattress is crooked, re-center it with two adults when possible.
• If it slides back out of place, check for a stretched cover, shifted internal parts, missing attachment points, or base movement.

2. Measure the Mattress Cover

Measure the mattress width in three places: at the head, in the middle, and at the foot. Measure from the widest point side to side. A second person can help you get a more accurate measurement.

• Write down all three measurements.
• Compare the head, middle, and foot measurements to each other.
• If one area is much wider, bowed, or stretched compared with the others, the cover, foam, or internal layers may have shifted or lost shape.
• If your mattress is more than about 1 inch wider than the base on a FlexFit adjustable base, or if the overhang is several inches, continue troubleshooting or contact support.

Important: Measurements help support understand whether the cover may be stretched. If you are not sure what your measurements should be, share the three measurements with support along with your mattress size and model.

3. Check for Shifted Foam or Internal Layers

• If your mattress cover opens, unzip it carefully and check that the foam rails, comfort layers, and air chambers are flat and centered.
• Look for foam that is torn, compressed, folded, bowed, or no longer supporting the edge.
• If the mattress “guts” look shifted to one side, gently reposition the layers so they sit evenly inside the cover.
• If foam is torn or has lost its shape, a replacement part or support review may be needed.

4. Check Air Level and Hose Connections

• If one side is lower or will not inflate, confirm both sides are set to 100 and wait a few minutes.
• Check that hoses are connected securely and are not pinched, bent, pulled loose, or trapped by a shifted mattress.
• If one side fills and then loses air, or the edge gets soft again after you adjust it, contact support for help checking for air loss.
• If you cannot disconnect a hose safely, do not force it. Contact support for next steps.

5. For FlexFit Adjustable Base Owners

Please note: A FlexFit adjustable base is usually about 1 inch narrower than the mattress so it can fit into 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 looks crooked even after re-centering, check the mattress attachment points and the Mattress Sliding on Base guide.

If your mattress uses magnets, straps, clips, or other attachment points, make sure they are aligned and attached. If the cover rotates, stretches, or pulls the attachments out of position, support may need to review replacement cover or service options.

When to Contact Support

• The mattress still hangs over the base after re-centering.
• The mattress hangs over the foot or side by several inches.
• One side will not inflate, loses air, or feels much softer than the other.
• Foam, the cover, magnets, straps, or attachment points look torn, stretched, missing, or out of place.
• The mattress feels unsafe, like you may roll off or fall.
• You need help with replacement parts, warranty options, or in-home service.

Frequently Asked Questions

Why does my mattress hang over the base?
Your mattress may hang over the base because it is not centered, the cover is stretched, the foam or air chamber has shifted, the base is narrower than the mattress, or one side is not inflating evenly.

What do I do after I measure my mattress?
Write down the head, middle, and foot measurements. If one area is much wider, bowed, or stretched, share the measurements with support along with your mattress size and model so they can help determine whether the cover, foam, or internal parts need review.

Is it normal for my FlexFit base to be narrower than my mattress?
Yes. A FlexFit adjustable base is usually about 1 inch narrower than the mattress. More than about 1 inch of overhang, sliding, crooked alignment, or foot overhang may need more troubleshooting.

Why does one side look lower than the other?
One side may be set lower, may not be filling fully, may have a hose connection issue, or may be losing air. Set both sides to 100, check the hose connections, and contact support if one side still will not inflate or hold air.

Can I replace my mattress cover, foam, or other parts?
Some parts may be replaceable depending on your mattress model and warranty. Contact support with your mattress size, model, purchase details, photos, and measurements if available.