30x40 Concrete Slab Cost Worksheet by Thickness

A 30 by 40 foot slab covers 1,200 square feet and contains about 14.8 cubic yards at 4 inches or 22.2 at 6 inches before allowance. Confirm the required section, then apply local quotes for the complete base, reinforcement, concrete, equipment and finish scope.

Illustrative cost inputs for a 30x40 concrete slab

The table demonstrates multiplication for three assumed rates and stated example scopes. This is an assumed input range, not observed data or a ranking of specifications.

Illustrative calculation inputs only. Replace every price with a current, scope-matched local quote.
Example scope	Assumed input per sq ft	Illustrative 30x40 result
4 in, basic broom finish	6 to 7 dollars	7,200 to 8,400 dollars
5 in, mesh reinforced	7 to 9 dollars	8,400 to 10,800 dollars
6 in, rebar + gravel base	9 to 12 dollars	10,800 to 14,400 dollars

Enter approved dimensions in the concrete slab calculator for quantities, then apply a current scope-matched quote.

How much concrete a 30x40 slab needs by thickness

Thickness drives the material cost more than anything else. Volume is length times width times thickness in feet, divided by 27 to get cubic yards. For 1,200 square feet, a 4 inch slab works out to about 14.8 cubic yards, and a 6 inch slab to about 22.2 cubic yards.

Cubic yards = 30 x 40 x (thickness in ÷ 12) ÷ 27

Every extra inch across the full footprint adds roughly 3.7 cubic yards, so moving from 4 to 6 inches is about 50 percent more concrete. Order 10 to 15 percent over the calculated volume for waste and an uneven subgrade.

Thickness	Cubic yards	+10% waste	Cubic meters
4 in	14.8	16.3	12.5
5 in	18.5	20.4	15.6
6 in	22.2	24.4	18.7

Labor and materials on a 1,200 square foot pour

Greater thickness increases concrete volume. Labor, equipment, base, reinforcement and finishing do not follow one fixed percentage, so request separate current prices for the approved section and compare the same scope.

Add-ons that change the price: rebar, gravel and prep

Price only the base, reinforcement, vapor control and site work required by the approved design and site conditions.

Illustrative calculation inputs only. Replace every price with a current, scope-matched local quote.
Add-on	Assumed input per sq ft	Illustrative 30x40 result
Rebar or wire mesh	0.20 to 0.50 dollars	240 to 600 dollars
Gravel base	1 to 2 dollars	1,200 to 2,400 dollars
Grading and site prep	varies	500 to 2,000 dollars
Vapor barrier	0.50 to 0.80 dollars	600 to 960 dollars

Use the specified slab section, reinforcement, subbase and vapor-control details. The assumed inputs do not select or validate those details.

Request itemized bids so omitted and included scope remains visible.

A contractor placing rebar in a wooden form before pouring a 1200 square foot concrete slab

What thickness a 30x40 slab should be

Thickness and reinforcement are design inputs governed by loads, support, concrete properties, joints and applicable requirements. Obtain the approved section before calculating quantity.

The calculator does not predict service life from thickness. Use the project documents and local requirements, then enter those dimensions for volume.

For a garage or building pad, include any specified edge thickening and reinforcement in the takeoff.

How location and finish affect the quote

State the 30x40 slab section, reinforcement, finish, curing and site preparation in each quote.

Ask for each finish as a separate option with its materials, preparation, curing, sealing and maintenance scope stated.

Use the concrete slab calculator for a quantity baseline, then apply the bidder's current rates.

By Calcnaut

Formula and declared-case checks run during the build; sources are listed for readers to review. Read our method and editorial policy.

Published 2026-07-03 Updated 2026-09-13

Illustrative worksheet, not a quote. These dollar figures are illustrative assumptions, not market data. Replace every rate with a current local quote for the stated scope: All monetary tables and examples on this page; replace rates with current, scope-matched local quotes.

Frequently asked questions

How much does a 30x40 concrete slab cost?

The page's illustrative scenarios multiply 1,200 square feet by assumed rates of $6 to $12, producing $7,200 to $14,400 across different stated scopes. These are not market quotes. Replace the applicable rate with a current bid for the approved section, base, reinforcement, concrete, finish and site work.

How many yards of concrete for a 30x40 slab?

A 30x40 slab needs about 14.8 cubic yards at 4 inches thick and about 22.2 cubic yards at 6 inches. Add 10 to 15 percent for waste, so order roughly 16 to 17 yards for a 4 inch pour and 24 to 26 yards for a 6 inch pour.

How should I compare 4-inch and 6-inch 30x40 slab budgets?

A 6-inch slab uses 50% more concrete than a 4-inch slab over the same 1,200-square-foot area: about 22.2 versus 14.8 cubic yards before allowance. Compare the approved alternatives with base, reinforcement, concrete, joints, finish, curing and site preparation all stated; do not apply a fixed cost premium.

How much does labor cost to pour a 30x40 slab?

No verified labor rate is supplied. Ask bidders to itemize layout, excavation, base preparation, forms, reinforcement, placing, equipment, finishing, curing and cleanup for the approved 30x40 slab, then compare the same scope.

How long does it take to pour a 30x40 slab?

Construction and loading schedules depend on crew, access, mixture, temperature, curing method and the project specification. Obtain placement, curing and loading criteria for the approved mixture rather than relying on a generic elapsed-time rule.

Sources and references

These references and structured source records support the method and material data used on this page.

30x40 Concrete Slab Cost Worksheet

Key takeaways