How to Measure Mattress Sag: Check Your Bed's Support

Quick reality check: is it sag or just a body impression?

Lay a straightedge (level or a long yardstick) across the mattress where you sleep, then slide a ruler down to the deepest point. Measure without anyone on the bed, sheets off. If that dip is around 1 to 1.5 inches or more, most brands call that sag. Under that? It may be a normal body impression. Materials matter: plush memory foam shows impressions sooner; latex is bouncier and tends to hold its shape longer. This simple approach is the fastest way to start on How to Measure Mattress Sag without any fancy tools.

While you’re at it, look underneath. Slats spaced wider than about 3 inches let foam push through and exaggerate dips. A bowed box spring can fake a sag too. Rotate the mattress 180 degrees and re-measure the same spot later in the week. Consistent numbers tell you it’s the bed, not the base. And if you’re documenting for a warranty, repeat the exact same How to Measure Mattress Sag steps in daylight and snap clear photos with the ruler in frame.

If you need extra support, shop for these build cues

Believe it or not, it’s not the buzzwords—it’s the guts. In hybrids, look for tempered steel coils (firmer 13–14 gauge feels sturdier), plus a real support foam under the comfort layers. In all-foam beds, density is king: polyfoam cores at 1.8 pounds per cubic foot or higher resist early bowing; true high-resiliency foam is 2.0 PCF+. For memory foam, 4+ PCF feels pressure-relieving without melting into a crater, and if you’re heavier or a hot sleeper, firmer, denser layers help the surface last. Zoned support (slightly firmer coils or foam under your hips) keeps spines happy long term. If a review sounds hand-wavy, verify claims the same way you learned How to Measure Mattress Sag—by checking what actually holds your weight.

Edges matter too. Mattresses with reinforced perimeters (thicker-gauge coils around the border or sturdy rails) won’t collapse when you sit to lace shoes. And foundations are half the story: solid platforms or tight slats under 3 inches apart keep foams from drifting. If you use an adjustable base, make sure the mattress is rated for it; flex can stress weak builds. Last bit: ultra-plush euro tops feel dreamy for a month and then, poof, the loft relaxes. If you love soft, pick quality density underneath so the comfort stays cushy without caving.

Fix it vs replace it: where I draw the line

If the dip is under an inch and you’re otherwise comfy, try a rotation routine every 1–3 months. Add a bunkie board or a sheet of flat, furniture-grade plywood between the slats and mattress to firm up the base. Still sagging? Measure again. Warranties usually kick in around 1.5 inches for springs/hybrids and about 1 inch for many foam beds—document it clearly. When I file a claim, I follow the same How to Measure Mattress Sag steps, take photos with good lighting, and note the spot and depth in plain language.

Here’s my personal rule: if I’m waking up sore, rolling toward the middle, or the edge squishes flat, I stop tinkering and replace. Toppers can soften feel but won’t fix a weak core. Most good beds last 7–10 years, but body type, climate, and use matter. If your mattress is young and sagging, it’s a design problem; if it’s older and tired, treat yourself to better bones.

Mattress types that hold up, in real life

All-latex builds are the quiet workhorses—buoyant, breathable, and tough. Hybrids with tempered coils and high-density foams balance support and pressure relief without the mid-span droop. True high-resiliency polyfoam (2.0 PCF+) can be wonderfully durable if the layers are thoughtfully stacked. What gives out faster? Ultra-soft pillow-tops stuffed with low-density foam, especially on a flimsy base. If you want my short list of mattresses with legit edge-to-edge support, check my product reviews on Consumer's Best—I keep it simple and call out the build specs that actually matter.

Bottom line

Don’t guess—measure. If the numbers say it’s sagging, you can fix the base, file a warranty, or upgrade to a build that won’t fold under you. And if you’re ready to switch, I’ve already done the homework. Tap into my no-nonsense picks on Consumer's Best and grab something that hugs where you want it—and holds you up where you need it.