Square Foot Pricing and Why Quotes Differ So Much

Two bids landed on the same 900 square foot driveway last spring: $6,500 and $11,200. Same square footage, same broom finish, same street. I know both crews and neither was trying to rob anybody. The entire spread sat in work that happens before a single form goes up. The high bid carried 42 cubic yards of export, 23 tons of imported base and two rounds of density testing. The low bid said “fine grade and pour.”

My whole trade is the part that gets buried, so I spend a lot of time explaining why the number everybody compares, dollars per square foot, is the one that hides the most.

The concrete is not the variable

Ready-mix delivered runs around $150 to $210 per cubic yard in most markets, plus short-load fees of $75 to $250 under about six yards. A 900 square foot driveway at 5 inches thick is roughly 14 yards, call it $2,400 in material. Every bidder buys from the same two or three plants at close to the same price, and placing labor varies but not by double.

What varies by double is the dirt. Two lots that look identical from the street can be a $1,000 site and a $6,000 site.

The line items nobody puts on the flyer

• Demolition and haul-off: $2 to $6 per square foot for existing concrete, plus $30 to $90 per ton in disposal.
• Excavation and export: $8 to $18 per cubic yard with machine access. Double it where no machine fits.
• Imported base: $35 to $65 per ton delivered for 3/4 inch minus crushed aggregate. Six inches under 900 square feet is about 23 tons, so $800 to $1,500 in rock before anybody spreads it.
• Undercut of soft material: $12 to $25 per cubic yard to dig out, plus import to replace it. This is the item that turns a bid into a surprise, which is why it belongs in the bid as a unit rate.
• Moisture conditioning: a water truck at $400 to $900 a day. Material has to sit within about 2 percent of optimum moisture to compact at all.
• Compaction equipment: plate compactor $70 to $110 a day, jumping jack $60 to $95, walk-behind roller $200 to $350, ride-on $400 to $700.
• Testing: a lab Proctor to set the target density is $250 to $450 per soil type; field density testing runs $150 to $300 an hour with a two to four hour minimum.

Testing is the first thing cut on residential work, and the only thing that turns “we compacted it” into a number on paper. When a bid says 95 percent compaction, the fair follow-up is 95 percent of what. Standard Proctor and modified Proctor use different compactive effort, and the modified target is meaningfully denser, so which ASTM standard the spec references changes how much work is actually required.

Why a cheaper bid can be completely honest

Sometimes the site really is good. A lot cut into firm granular ground, no export, no soft spots, does not need $4,000 of earthwork. I have written low numbers on plenty of jobs because the dirt was already what I wanted.

The problem is not a low number. It is a low number with no scope attached, because when the excavator hits 18 inches of soft fill on day one, that work still happens, now as a change order at whatever price the moment allows.

Three questions that make bids comparable

1. How many inches of what material, compacted to what percentage of which Proctor, verified how? “Compacted base” is not a specification. “6 inches of 3/4 inch minus in two lifts to 95 percent of modified Proctor, one density test per 2,500 square feet” is one.
2. What is the unit price if soft material is found? Get a dollars-per-cubic-yard figure for undercut written in before work starts. A bidder who prices that risk openly is being clear.
3. Who hauls the spoil, and is the dump fee inside the number? On a full replacement this is routinely $600 to $1,500 hiding in one bid and not the other.

The rest of the sheet deserves the same treatment: reading a concrete bid line by line covers the concrete half.

What the spread usually looks like

Nationally, a plain 4 inch broom-finish slab on decent ground lands around $6 to $10 per square foot. A 5 to 6 inch reinforced slab over a properly built and tested base is more like $9 to $16. Truck-rated work, bad access, or heavy undercut pushes it to $14 to $22. When two bids differ by more than roughly 30 percent, the difference is almost never in the concrete.

Frequently asked questions

Why is one contractor $3 per square foot cheaper than everyone else? Usually because the scope stops at the surface. Compare base thickness, compaction target, testing and disposal line by line and the gap normally accounts for itself. If it does not, the low bidder may carry less overhead, or may plan to make it back in change orders.

Is compaction testing worth paying for on a residential driveway? On a flat lot over firm native ground, often no. On engineered fill, across a utility trench, on a lot less than about five years old, or under anything a truck will park on, yes. A $400 test is cheap alongside a $9,000 replacement.

Does a per-square-foot price mean anything at all? It is a sanity check and nothing more. It works for comparing finishes and thicknesses on the same site, and falls apart across sites, because the ground under two identical-looking driveways can differ by a factor of five in cost to make ready. Mechanical quotes fall apart on the same logic — an HVAC contractor in Roswell pricing by tonnage without a load calculation is guessing in the same way.

Trade body: American Society of Concrete Contractors.