Before you call a contractor — or decide you don't need one yet — measure the drop. A straightedge, a tape measure, and ten minutes tell you whether you're looking at a cosmetic dip, a lift candidate, or a problem with an active cause that needs attention now.
Almost every homeowner discovers sunken concrete the same way: they trip on it, notice water pooling where it never used to, or catch the uneven edge out of the corner of an eye. The eye is good at noticing a problem and terrible at sizing it. A slab that "looks like it's down a couple inches" might be down half an inch, and a slab that looks fine in flat afternoon light might be down a full inch on the side facing the house, quietly sending rainwater toward the foundation.
The number matters because it drives every decision that follows. It decides whether you monitor or act, whether the fix is a lift or something bigger, and roughly what the fix costs — lifting is priced by area and depth, so a slab down half an inch needs less material than the same slab down two inches. It also gives a contractor something concrete to work with (pun intended) before anyone visits, and it gives you a baseline: measure again in a month or two, and you know whether the slab is stable or still moving. That single fact — stable versus moving — is the most important thing a contractor learns on a first visit, and you can hand it to them for free.
Utah homeowners have one more reason to measure rather than guess. The Salt Lake Valley's soils — lakebed clays on the west side, sandier benches on the east, and recompacted hillside fill in newer subdivisions — move with moisture and with the seasons. A slab measured in August, when clay soils have shrunk dry, can read differently from the same slab measured in April after snowmelt. That is not a reason to skip measuring; it is a reason to measure twice, in different conditions, and to write both numbers down. The background on why Utah concrete settles explains which soil you are likely standing on.
You do not need surveying gear. For nearly every residential slab, four things are enough:
A laser level is a nice upgrade for long runs like a full driveway, because it projects a reference line across the whole surface at once. It is a convenience, not a requirement. A water level — a length of clear tubing filled with water — is the old-school equivalent and costs almost nothing, though it is fiddly for a first-timer. Skip the fancy options until you have done the straightedge method once; it answers the question for most slabs.
Start by finding the high ground. Walk the slab and identify the sections that have not moved — usually the sections tight against the garage floor, the foundation, or a section that still lines up with its neighbor. Your straightedge needs to rest on those stable sections, bridging over the dip. If the whole area has dropped, rest one end on the nearest stable feature (a step, a curb, the garage slab) and note that your measurement is relative to that feature.
Lay the straightedge across the dip and slide the tape measure underneath at the deepest point. Read the gap where the tape meets the straightedge, not where it meets the slab — the tape should stand vertically, and the reading is the distance from the slab surface up to the bottom of the straightedge. Repeat at several points: the middle of the dip, both edges, and anywhere water pools. A single number hides the pattern, and the pattern is diagnostic. A dip deepest in the middle suggests soil consolidation or washout under the center. A tilt — one side low, the other level — suggests water or soil acting on one side, or a slab that has rotated. A step between two adjacent panels, where one panel is uniformly lower than its neighbor, points at the joint between them, often with a void underneath.
Next, check for offset at the joints. Run your hand or a ruler across each joint around the sunken area. If one side of a joint sits higher than the other, that is vertical displacement, and it matters more than the absolute drop: a half-inch offset at a joint is a trip hazard even if the slab's overall drop is modest, and it tells a contractor the panels are moving independently. Note every offset joint and its height difference.
Then do the tap test. Walk the slab tapping it firmly with a hammer handle or the heel of your shoe. Solid concrete gives a dull thud; a slab with a void underneath gives a hollow thunk. Map the hollow areas roughly — they mark where soil has washed out or consolidated, and they are the areas a lifting contractor will target. The hollow-sound check is covered in more depth in our concrete void filling guide.
Finally, look at the water. Pour a bucket of water on the high side of the slab (or just watch the next rainstorm) and see where it goes. Water that drains away from the house and off the slab is fine. Water that pools in the dip, or runs toward the foundation, turns a measurement into an urgency: standing water erodes the soil underneath and freezes in winter, so a dip that holds water gets worse faster than a dry one.
| Measured drop | What it usually means | Reasonable next step |
|---|---|---|
| Under 1/4 inch | Cosmetic; often seasonal movement or original finishing variation | Monitor; re-measure in 2–3 months and after a wet season |
| 1/4 to 1/2 inch | Early settlement; trip hazard if it sits at a joint or walkway edge | Monitor closely, or get a quote if it is on a walkway or holds water |
| 1/2 to 1 inch | Clear settlement; drainage usually affected | Lift candidate — get quotes, and check drainage at the same time |
| 1 to 2 inches | Significant settlement; slab usually still sound and very liftable | Get a contractor out; ask what caused it, not just what the lift costs |
| Over 2 inches, or still growing | Active cause: water, washout, or weak soil | Prompt contractor visit; find and fix the cause alongside the lift |
Two caveats keep these numbers honest. First, location beats magnitude: a half-inch lip on a sidewalk where kids and grandparents walk is more urgent than a one-inch dip in the middle of a back patio nobody crosses. Second, change beats magnitude: a slab that dropped an inch five years ago and has not moved since is a simpler job than a slab that dropped half an inch in the last two months and is still going. That is why the second measurement matters as much as the first. A stable slab gets a lift; a moving slab gets a diagnosis first, and the lift second.
Tell us your measurements — the drop, the location, and whether it's still moving — and we'll give you a straight answer on whether it's a lift, a monitor-and-wait, or something that needs a closer look.
Most sunken flatwork — driveways, sidewalks, patios, garage floors — is a lifting contractor's job, and the measurement is what confirms it. Call a contractor when you find a drop of an inch or more, a trip hazard on any walkway, water pooling or draining toward the house, cracks that are widening or offset, or any slab that is still moving between your measurements. A good contractor will re-measure on site, probe the soil alongside the slab, and explain the cause before quoting — if someone quotes from photos alone without asking about the settlement history, get a second opinion. Our contractor selection guide covers the questions that separate the two.
The measurement says "call an engineer" when the movement involves the house itself rather than just the flatwork. The warning signs: cracks in the foundation wall, stair-step cracking in brick or block, doors or windows that suddenly stick, floors inside the house that slope, or a slab (like a basement floor) that is moving with the walls. Flatwork lifting fixes slabs; it does not fix foundations, and injecting material under a foundation problem can make the diagnosis harder. A structural engineer gives you a stamped opinion on what is moving and why, and then the right contractor — foundation or flatwork — does the work. The foundation vs. slab settlement guide walks through the distinction in detail.
One more measurement worth taking while you are out there: the gap between the slab and the house. A driveway or patio pulling away from the foundation leaves a gap that funnels water straight down alongside the footing — the worst place for it. Note the gap width and whether it is growing, and mention it to the contractor. It is often fixed as part of the lift, but only if someone knows to look.
The honest summary is simple. Ten minutes with a straightedge gives you the drop, the pattern, and — if you repeat it — the direction of travel. Those three facts decide whether you monitor, lift, or investigate further, and they keep any contractor honest, because you already know the answer before they arrive. If your numbers land in the lift-candidate range, the next step is a quote, and the pricing anchor is the published range: mudjacking at $3–$8 per square foot, polyurethane foam at $5–$25 per square foot, with most residential jobs landing between $500 and $3,000 total. The full tables are in the cost guide, and how concrete lifting works explains what happens on lift day.
The simplest reliable method is a straightedge and a tape measure: lay a long level or straight board across the sunken slab so it rests on the high, stable sections on either side, then measure the gap between the straightedge and the low slab at its deepest point. That gap is your drop. A 4-foot level works for a sidewalk square; a longer board or a taut string line works for driveways and patios. Measure at several points and write each one down — a single number hides the pattern.
As a practical rule of thumb: under a quarter inch is usually cosmetic — monitor it and re-measure in a few months. Around half an inch, a sidewalk lip becomes a real trip hazard and a driveway starts catching water, and that is when most homeowners start getting quotes. At one to two inches, the slab is a strong lift candidate, because the drop is large enough to affect drainage and safety but the slab is usually still sound. Beyond two inches, or any drop that is still growing, get a contractor out promptly — the underlying cause is active, and the longer it runs, the more material the fix takes.
A regular 4-foot level, a straight 8-foot board, a tape measure, and your phone camera cover nearly every residential measurement. A laser level helps on long driveways because it gives you a reference line across the whole run, but it is a convenience, not a requirement. What matters is a straight reference spanning from stable concrete to stable concrete — a short level balanced on the sunken slab itself tells you nothing, because it just sits in the dip.
Yes, if you have the time — two measurements a few weeks apart, in different weather, tell you something one measurement cannot: whether the slab is still moving. A slab that dropped an inch years ago and has not moved since is a straightforward lift. A slab that dropped another quarter inch between your two measurements has an active cause — water, soil, or a leak — that needs to be found before or alongside the lift, or the repair will not hold. See the signs your concrete is sinking for what else to watch.
Because measurements without context are easy to misread later — including by you. Photograph the straightedge in place with the tape showing the gap, photograph the whole slab from the same angle each time, and photograph the edges where the slab meets the garage floor, steps, or foundation. Dated photos give a contractor a head start on the diagnosis, document the problem for an HOA or an insurance conversation, and let you prove whether the problem is stable or growing. If you ever sell, that record is worth having too — see selling a home with uneven concrete.
Yes — pooling water turns a small drop into a bigger problem. Standing water seeps into joints and cracks, erodes the soil underneath, and in winter it freezes and heaves the slab, so a quarter-inch dip that holds water can become a one-inch dip faster than a dry slab would. If water is pooling, fix the drainage question at the same time as the lift — our drainage and settlement guide explains where that water usually comes from.
Call a contractor when any of these show up: a drop of an inch or more, a trip hazard on a walkway, water pooling or draining toward the house, cracks that are widening or offset (one side higher than the other), or a slab that is still moving between measurements. Call a structural engineer first — not a lifting contractor — if the movement involves the house itself: foundation cracks, sticking doors or windows, or walls pulling away. Our foundation vs. slab settlement guide explains how to tell the difference.