Concrete Slab Cost per Square Foot: How the Price Is Built

How much does it cost to pour a concrete slab?

Concrete slab cost per square foot is not one national number. It is the slab's cubic yards (square feet × thickness in inches ÷ 324) × your supplier's price per yard, plus short-load and delivery fees, any pump, the gravel base, forms, rebar or mesh, finishing labor and sales tax — all divided by the slab's square feet.

Published cost guides do print per-square-foot figures, and they disagree. HomeGuide publishes $6 to $12 per square foot installed; Homewyse publishes $10.33 to $12.65 per square foot for a basic 4-inch-plus slab that excludes excavation, gravel base and tax (both published figures checked 19 Sep 2026; prices change — get a written quote). The gap between two published ranges is the reason this guide builds the price line by line instead of quoting an average.

The practical workflow: work out the cubic yards, get a written ready-mix quote with every fee listed, add the site lines (base, forms, reinforcement, labor), apply tax, and divide by the slab area. The Ready-Mix Concrete Cost Calculator handles the concrete lines — billed volume, short-load minimums, loads, fees and tax — from the prices you type in.

Step 1: square feet to cubic yards (the ÷ 324 shortcut)

Ready-mix is sold by volume in cubic yards. A cubic yard is 27 cubic feet, and a slab thickness is given in inches, so cubic yards = length (ft) × width (ft) × thickness (in) ÷ 12 ÷ 27. Because 12 × 27 = 324, that simplifies to square feet × inches ÷ 324.

The table converts common slab sizes. It is pure geometry — no prices. The '+ 10%' column adds the top of the 4% to 10% ordering allowance that the National Ready Mixed Concrete Association (NRMCA) suggests for contingencies; your supplier then rounds to its own order increment.

Step 2: the line items that make up a slab price

A slab price is the sum of separate lines, each priced in its own unit. Ask for each one to be shown on the quote; a single lump sum hides which line is driving the cost per square foot.

Worked example: a 20 × 20 ft patio slab at 4 inches

The rates below are illustrative inputs you would type in — they are not market prices. Replace each one with the figure on your own written quote.

Volume: 20 × 20 = 400 sq ft. 400 × 4 ÷ 324 = 4.938 yd³, about 4.94 yd³.

Order quantity: add a 10% allowance: 4.938 × 1.10 = 5.432 yd³. If the supplier sells in quarter-yard steps, round up to 5.50 yd³. (Confirm the increment — it is a supplier rule, not a universal one.)

Concrete line at an illustrative $150 per yd³: 5.50 × 150 = $825.00. Short-load line at an illustrative $50 per yd³ (5.50 yd³ is below a 10 yd³ full load): 5.50 × 50 = $275.00. Delivered-concrete subtotal: 825 + 275 = $1,100.00.

Concrete-only cost per square foot: 1,100 ÷ 400 = $2.75. With an illustrative 7% sales tax: 1,100 × 1.07 = $1,177.00, and 1,177 ÷ 400 = $2.94 per sq ft (2.9425, rounded).

That $2.94 covers only the concrete. The gravel base (for example, a 4-inch base over the same 400 sq ft is another 400 × 4 ÷ 324 = 4.94 yd³ before its compaction allowance), 80 linear feet of form edge (20 + 20 + 20 + 20), reinforcement and labor are added on top. Final cost per sq ft = (every line + tax) ÷ 400.

• Slab length, width and thickness measured; cubic yards = sq ft × inches ÷ 324.
• Ordering allowance added (NRMCA suggests 4% to 10%) and rounded to the supplier's increment.
• Written ready-mix quote: price per yd³, short-load threshold and fee, delivery extras, standby rate.
• Pump quoted only if the truck cannot reach the forms.
• Base, forms, reinforcement and labor priced as separate lines.
• Tax basis confirmed, then total ÷ slab sq ft = cost per square foot.

What published cost guides report (checked 19 Sep 2026)

These are the figures printed on the named pages when they were checked on 19 September 2026. They are the publishers' figures, not BuildMeasure's, and they describe different scopes — read the 'covers' column before comparing. Prices change; get a written quote.

Common questions

Short answers to the ways people phrase the slab-cost question. Every published figure below is labelled with its source; your own price comes from your quotes.

• How much does it cost to pour a 20x20 concrete slab? — At 4 inches it is 4.94 yd³ of concrete (about 5.5 yd³ ordered with a 10% allowance rounded to a quarter yard). HomeGuide publishes $2,400 to $4,800 installed for a 20x20 slab (checked 19 Sep 2026). Your figure is the line items above priced by your supplier and contractor.
• What does a 10x10 concrete slab cost? — The concrete is only 1.23 yd³ at 4 inches, so fixed charges (short-load fee, delivery, minimum labor) dominate and the cost per square foot runs higher than on a big slab. HomeGuide publishes $600 to $1,200 installed (checked 19 Sep 2026). For small pads, compare bagged concrete against a short load.
• How much does a yard of concrete cost? — HomeGuide publishes $119 to $147 per cubic yard with delivery within 20 miles, plus about $53 per yard for loads under 10 yards (checked 19 Sep 2026). The yard price is only the first line of a slab quote.
• What is the cost to pour a concrete patio? — HomeGuide publishes $4 to $12 per square foot installed for a concrete patio (checked 19 Sep 2026). Build your own number with the patio's cubic yards, your quotes and the line items above.
• Does a 6-inch slab cost 50% more than a 4-inch slab? — The concrete line does: 400 sq ft at 6 in is 7.41 yd³ against 4.94 yd³. Forms, finishing and some fees do not scale the same way, so the total usually rises by less than the concrete line alone.

Mistakes that make a slab estimate look cheaper than the invoice

Most budget overruns come from lines that were never on the estimate rather than from a wrong price per yard.

• Pricing exact volume with no allowance — subgrade dips and form spread use concrete, and a second truck costs another delivery.
• Ignoring the short-load fee on a small order; it can change the effective price per yard substantially.
• Leaving out the gravel base, forms and reinforcement because they are 'not concrete'.
• Comparing a per-square-foot figure that includes labor with a per-yard figure that does not.
• Forgetting standby time: a truck kept waiting because forms or crew are not ready can be billed by the minute.
• Assuming the quote includes tax without asking.

Same project

Related measurement guides

• How much does a yard of concrete cover? →
• Concrete order quantities explained →
• Ready-mix vs bagged concrete →
• Gravel base under a concrete slab →
• How to plan a concrete slab pour →

Sources and limits

Check the project-specific details

• HomeGuide — How Much Does a Concrete Slab Cost? — Publishes $6–$12 per sq ft installed, materials $3–$7 and labor $3–$5 per sq ft, and a size table including 10x10 $600–$1,200, 12x12 $860–$1,700 and 20x20 $2,400–$4,800; patio $4–$12 per sq ft installed. Published price checked 19 Sep 2026; prices change — get a written quote.
• HomeGuide — How Much Does Concrete Cost Per Yard? — Publishes $119–$147 per yd³ with delivery up to 20 miles, + $53 per yd³ for less than 10 yd³ per load, + $8 per yd³ Saturday, + $9.50 per mile beyond 20 miles, + $3 per minute standby, and pump rates ($15 per yd³ with $125 minimum; boom $140–$190 per hour). Published price checked 19 Sep 2026; prices change — get a written quote.
• Homewyse — Cost to Install Cement Slab — Publishes $10.33–$12.65 per sq ft (May 2026 pricing) for a basic 4+ inch, 3500 psi fibermesh slab with broom finish including labor, supplies and equipment, and lists exclusions: excavation, gravel base, compaction, demolition, contractor overhead, sales tax and permits. Published price checked 19 Sep 2026; prices change — get a written quote.
• NRMCA — CIP 31: Ordering Ready Mixed Concrete — States concrete is sold by volume in cubic yards, truck mixers carry 8 to 12 cubic yards, and the quantity ordered should be 4% to 10% more than the plan-dimension estimate — the basis for the allowance column and worked example.

Review status: Formulas and worked examples checked by hand; measurement practice pending human trade review.

This guide supports planning only. It does not specify structural design, code compliance, or a supplier quotation.