How Much Concrete Do I Need? Cubic Yards, Bags and 2026 Costs

Multiply length × width × thickness in feet and divide by 27 to get cubic yards: a 10 ft × 10 ft slab 4 in thick is 1.23 cubic yards, or about 56 bags of 80 lb mix. Add 4–10% for waste; ready-mix runs $160–195 per cubic yard in 2026.

How to calculate concrete volume in cubic yards

Concrete is sold by volume, not by area or weight: ready-mix plants quote and bill in cubic yards of fresh, unhardened concrete, so the number that matters before you order is the volume of the pour. The same formula covers a slab, a footing, a pad, and a wall — length × width × depth, all in feet, divided by 27, the number of cubic feet in a cubic yard (3 ft × 3 ft × 3 ft).

Thickness is almost always measured in inches while the plan is measured in feet, so convert it first by dividing by 12:

Cubic yards = (length ft × width ft × thickness in ÷ 12) ÷ 27

There is a one-step shortcut: divide by 324 instead, which is simply 12 × 27. A 10 ft × 10 ft slab at 4 in thick is (10 × 10 × 4) ÷ 324 = 1.23 cubic yards. Checked the long way: 100 sq ft × 0.333 ft of depth = 33.3 cubic feet, and 33.3 ÷ 27 = 1.23 cubic yards.

Two mistakes account for most short pours. The first is unit mixing — "a yard of concrete" always means a cubic yard of volume, never 3 linear feet or 9 square feet, which is why those same 1.23 cubic yards fill a 10 × 10 patio at 4 in but only 33 sq ft of a wall poured 12 in thick. The second is thickness drift: NRMCA notes that on a 4 in slab, being just 1/8 in deeper than the dimension used in the estimate shortens the pour by about 3%, which is a full yard short on a 32 cubic yard order.

Cubic yards vs bags: how much concrete is in a bag

Bagged pre-mix is labeled by the volume of concrete it makes, ready-mix is ordered by the cubic yard, and you have to pick one before you buy. QUIKRETE's data sheet for its Crack Resistant Concrete Mix states that an 80 lb bag yields approximately 0.6 cubic feet of mixed concrete — 0.0075 cubic feet per pound — so a 60 lb bag makes about 0.45 cubic feet and a 40 lb bag about 0.30.

Bag size	Mixed concrete per bag	Bags per cubic yard	Best for
40 lb	0.30 cu ft	90	Post holes, small repairs, touch-ups
60 lb	0.45 cu ft	60	Fence posts, steps, small pads
80 lb	0.60 cu ft	45	Patios, walkways, and pads under 1 yd³

One cubic yard is 27 cubic feet, so it takes about 45 bags of 80 lb mix to equal one cubic yard — 60 bags if you buy the 60 lb size, 90 if you buy 40 lb. That number is the crossover that decides your purchase: past roughly one cubic yard, hand-mixing stops paying. Filling a yard from bags means opening, mixing, and placing 45 bags of about 80 lb each — close to 3,600 lb of material moved by hand — while one ready-mix truck delivers and discharges the same volume in minutes.

Bagged mix is also a lower-strength product. The QUIKRETE sheet rates that mix at 4,000 psi at 28 days, which is fine for patios, walkways, and shed pads; ready-mix plants typically quote 3,500 to 5,000 psi mixes for the same residential work. For anything structural, the truck wins on strength and labor at the same time.

How thick should the slab be? Thickness and volume by project

Thickness is the variable you control, and it moves the volume more than most people expect: going from 4 in to 8 in doubles the concrete even though the footprint never changed. For a 100 sq ft area the numbers run like this:

Thickness	Cubic feet per 100 sq ft	Cubic yards per 100 sq ft	Common use
4 in	33.3 cu ft	1.23 yd³	Patios, walkways, sidewalks, shed pads
5 in	41.7 cu ft	1.54 yd³	Driveway aprons and approaches
6 in	50.0 cu ft	1.85 yd³	Driveways, garage slabs, RV pads
8 in	66.7 cu ft	2.47 yd³	Heavy equipment pads

Typical thicknesses follow the load. A university design standard for concrete sidewalks specifies 4 in at the footway and 6 in at the driveway apron, while QUIKRETE's installation instructions call for sidewalks and patios at least 4 in thick. What sits under the slab matters as much as the slab: the same standard places the concrete on 6 in of compacted gravel sub-base over compacted subgrade, with a minimum compressive strength of 4,500 psi at 28 days and 6% ± 1% entrained air for freeze-thaw exposure.

Plan the joints while you are at it, because all concrete shrinks and cracks. That standard cuts control joints 1/8 in wide to at least one quarter of the slab depth, with expansion joints every 8 ft on center; QUIKRETE's flatwork instructions call for 1 in deep grooves every 6 to 8 ft so the cracks open where they are least visible.

Waste allowance, truck size, and how to prepare the order

Volume from the plan dimensions is the theoretical minimum, and NRMCA's ordering guide is explicit that it is not the purchase: the quantity ordered should be 4% to 10% more than an estimate calculated from plan dimensions to account for contingencies. Its companion bulletin on yield repeats the allowance for waste, over-excavation, and placement dimensions larger than nominal, and notes that concrete hardened in place can finish about 2% smaller than the same concrete measured fresh, through lost air, bleeding, and drying shrinkage.

Work a driveway: 20 ft × 24 ft at 5 in is 480 sq ft × 0.417 ft = 200 cubic feet = 7.41 cubic yards. A 10% allowance brings it to 8.15 cubic yards, so an order of 8.5 cubic yards covers the forms without a second truck. On a small patio — 12 ft × 12 ft at 4 in = 1.78 cubic yards — the same 10% adds 0.18 cubic yard, which is roughly one extra 80 lb bag if you are pouring from bags.

Then match the order to the truck. NRMCA puts truck mixer capacity at 8 to 12 cubic yards, and a full residential load is commonly about 10 cubic yards at $1,169 to $1,444 delivered; anything less than a full load is a short load and adds roughly $53 per cubic yard, with mileage beyond 20 miles billed at about $9.50 per mile. Scheduling matters more than price at the margin: a loaded concrete truck weighs about 80,000 lb and needs firm, unobstructed access, and fresh concrete normally sets and hardens within two to eight hours of mixing, with roughly 90 minutes or 300 drum revolutions to discharge. Finally, recheck the quantity as the pour progresses — NRMCA's advice is to re-evaluate the volume required and tell the producer early enough to adjust the following loads, rather than ordering a small clean-up load at the end.

What concrete costs in 2026

Ready-mix pricing for 2026 runs about $160 to $195 or more per cubic yard nationwide, after a national average of $179.95 per cubic yard in 2025, and a plain slab poured by a contractor lands between $6.50 and $10.50 per square foot with material and labor included. Cost guides that price the concrete alone put delivery within 20 miles at $119 to $147 per cubic yard; the gap between the two ranges is the forming, subbase prep, and finishing that turn a pile of concrete into a slab.

Project	Size and thickness	Cubic yards	Concrete only at $180/yd	Installed at $6.50–$10.50/sq ft
Patio	10 × 10 ft, 4 in	1.23 yd³	$221	$650–$1,050
Patio	12 × 12 ft, 4 in	1.78 yd³	$320	$936–$1,512
Garage slab	24 × 24 ft, 4 in	7.11 yd³	$1,280	$3,744–$6,048
Driveway	20 × 24 ft, 5 in	7.41 yd³	$1,334	$3,120–$5,040

Two line items decide the final invoice: delivery beyond 20 miles from the plant adds about $9.50 per mile, and every cubic yard under a full 10-yard load carries the $53 short-load charge — which is why a 1.78 cubic yard patio can cost nearly as much for concrete as a 4 cubic yard pour. Under roughly one cubic yard, bags usually win: 45 to 60 bags per yard at retail, plus your own mixing labor.

Frequently asked questions

How many cubic yards of concrete do I need for a 10x10 slab?

At 4 in thick it takes 1.23 cubic yards — 100 sq ft × 0.333 ft = 33.3 cubic feet, divided by 27. Add the waste allowance and order about 1.4 cubic yards. In bags that is about 56 bags of 80 lb mix before waste and 62 after it.

How many 80 lb bags of concrete are in a cubic yard?

About 45. An 80 lb bag yields roughly 0.6 cubic feet of mixed concrete and a cubic yard is 27 cubic feet, so 27 ÷ 0.6 = 45 bags. With the usual 10% waste allowance, plan on 50 bags per yard.

How much extra concrete should I order for waste?

NRMCA recommends ordering 4% to 10% more than the volume calculated from plan dimensions. Use 10% for DIY pours, uneven subgrade, or over-excavated footings and 5% for clean, well-braced forms — on a 100 sq ft slab at 4 in, that is 0.06 to 0.12 cubic yard of extra concrete.

How much does a yard of concrete cost in 2026?

Ready-mix runs about $160 to $195 or more per cubic yard nationwide in 2026, after a $179.95 average in 2025. Cost guides price concrete delivered within 20 miles at $119 to $147 per cubic yard, and ordering less than a full 10-yard load adds roughly $53 per cubic yard.

How much does a cubic yard of concrete weigh?

About 4,050 lb, or just over 2 short tons. Normal-weight concrete is designed at 150 lb per cubic foot and a cubic yard holds 27 cubic feet. A loaded ready-mix truck carries roughly 80,000 lb, so check the access before delivery day.

How long does concrete take to set and reach full strength?

Fresh concrete normally sets and hardens within two to eight hours of mixing, but it keeps gaining strength for years. Design strength is verified at 28 days, and 3,500 to 5,000 psi is the typical specified range for residential work; sidewalk specifications commonly call for 4,500 psi at 28 days.