Concrete Slab Cost Calculator
Price a concrete slab or pad from your own local quotes: enter the size, your bag price and your ready-mix quote with its fees, and see what each way of buying the concrete costs, the cost per square foot and the slab size at which the truck becomes cheaper.
Quick answer
Concrete slab cost = volume × your local price. A 10×10 ft slab 4 in thick needs 1.36 yd³ with 10% waste: 62 bags of 80 lb mix, or a 1.5 yd³ ready-mix order. Bags usually win on small pads; ready-mix wins once short-load and delivery fees are spread over enough yards. The calculator finds that break-even for your prices.
Published 2026-10-20 · No built-in prices: every dollar figure comes from you. Bag yields and mixing water are from Quikrete's Concrete Mix No. 1101 data sheet; the volume math is the same function as our concrete slab calculator.
What will my concrete slab cost?
Only the size is required. Leave a price blank and that option is skipped; leave a fee blank and it counts as $0.
Result
How to use the concrete slab cost calculator
- Enter length, width and the real pour depth. The waste allowance is applied to the volume before bags and truck yards are counted.
- Type the shelf price of the bag size you would buy, plus any mixer rental or bag delivery charge.
- Ask a local ready-mix supplier four things: price per yard, ordering step, minimum order, and the short-load threshold and fee. Enter what they quote, plus any delivery or fuel charge.
- Add forms, gravel, reinforcement or labor in "other costs" if you want a total project figure.
- Read the two totals, the cheaper option and the break-even line: it tells you how many yards your pour would need before the truck pays off.
Assumptions & formula
- Volume: V (ft³) = length (ft) × width (ft) × thickness (in) ÷ 12; cubic yards = ft³ ÷ 27; waste multiplies the volume by (1 + waste % ÷ 100). Same as
Calcs.concreteSlabin js/calcs.js. - Bags: bags = volume with waste ÷ bag yield, rounded up; yields 0.60 ft³ (80 lb), 0.45 ft³ (60 lb) and 0.30 ft³ (40 lb) from the Quikrete Concrete Mix No. 1101 data sheet. Bag cost = bags × your price + bag-route extras.
- Truck: ordered yards = volume with waste rounded up to the supplier's step, and never below the minimum order. Truck cost = ordered yards × your price per yard + short-load fee (only if the order is below the threshold you entered) + delivery fees.
- Cost per ft² and per yd³ = total (including "other costs") ÷ slab area, or ÷ slab volume without waste.
- Break-even: the calculator steps through volumes from 0.01 to 40 yd³ (0.01 yd³ at a time) and reports the smallest volume from which the truck is never dearer than bags, with your prices and fees, then converts it into slab area at your thickness.
- Not included: sales tax, waiting-time or Saturday charges, pump rental, finishing tools. Add any you know about to the fee fields.
When is ready-mix cheaper than bags?
Ready-mix becomes cheaper than bags once the pour is big enough to spread the truck's fixed fees: break-even volume ≈ truck fixed fees ÷ (bags per yard × bag price − ready-mix price per yard), where bags per yard is 45 for 80 lb bags. If 45 bags cost less than one yard from the truck, bags stay cheaper at every size, and only labor and time argue for the truck.
| Price gap per yard | Fees $100 | Fees $200 | Fees $300 | Fees $400 |
|---|---|---|---|---|
| $25/yd³ | 4.0 yd³ (324 ft²) | 8.0 yd³ (648 ft²) | 12.0 yd³ (972 ft²) | 16.0 yd³ (1296 ft²) |
| $50/yd³ | 2.0 yd³ (162 ft²) | 4.0 yd³ (324 ft²) | 6.0 yd³ (486 ft²) | 8.0 yd³ (648 ft²) |
| $100/yd³ | 1.0 yd³ (81 ft²) | 2.0 yd³ (162 ft²) | 3.0 yd³ (243 ft²) | 4.0 yd³ (324 ft²) |
| $150/yd³ | 0.7 yd³ (54 ft²) | 1.3 yd³ (108 ft²) | 2.0 yd³ (162 ft²) | 2.7 yd³ (216 ft²) |
| $200/yd³ | 0.5 yd³ (40 ft²) | 1.0 yd³ (81 ft²) | 1.5 yd³ (122 ft²) | 2.0 yd³ (162 ft²) |
Read it with your own numbers: work out 45 × your 80 lb bag price, subtract your ready-mix price per yard, then find the fee column closest to your supplier's short-load plus delivery charges. The calculator above does the exact version, including whole bags, the ordering step and a fee that disappears above the short-load threshold, which can make the cheaper option flip back and forth near that threshold.
Worked example: a 10×12 ft patio slab, 4 in thick
With the round example inputs below, a 10×12 ft patio slab 4 in thick costs $444.00 in bags and $500.00 by truck, so bags win by $56.00; the same inputs make the truck cheaper from about 2.58 yd³ (about 190 ft² at 4 in with 10% waste). These are example inputs to show the arithmetic, not prices we collected: replace them with your own.
| Step | Bags | Ready-mix truck |
|---|---|---|
| Slab volume | 10 × 12 × 4 ÷ 12 = 40 ft³ = 1.48 yd³; with 10% waste 44.0 ft³ = 1.63 yd³ | |
| Quantity | 44.0 ÷ 0.60 = 73.33 → 74 bags (5,920 lb) | 1.63 yd³ → order 1.75 yd³ (0.12 yd³ over) |
| Concrete | 74 × $6.00 = $444.00 | 1.75 × $200 = $350.00 |
| Fees | $0.00 | short-load $150.00 (order under 4 yd³) |
| Total | $444.00 | $500.00 |
| Per ft² (120 ft²) | $3.70 | $4.17 |
Grow the same pad to 16×20 ft and the answer flips: 196 bags cost $1,176.00, while the truck delivers 4.5 yd³ with no short-load fee for $900.00. Notice also the bag weight: 15,680 lb for the 16×20 slab, nearly 8 tons to lift twice, once into the cart and once into the mixer.
How many bags or yards does a concrete pad or slab take?
A 4 in concrete pad needs about 0.0136 yd³ per square foot with 10% waste, so a 10×10 ft slab takes 1.36 yd³ (62 bags of 80 lb) and a 20×20 ft slab 5.43 yd³ (245 bags). The table adds what a quarter-yard and half-yard ordering step would deliver, which is what you pay for on the truck side.
| Size | Thick | yd³ (no waste) | yd³ +10% | 80 lb bags | Bag weight | Order, 1/4 yd steps | Order, 1/2 yd steps |
|---|---|---|---|---|---|---|---|
| 4×4 ft | 4 in | 0.20 | 0.22 | 10 | 800 lb (0.4 tons) | 0.25 | 0.5 |
| 6×6 ft | 4 in | 0.44 | 0.49 | 22 | 1,760 lb (0.9 tons) | 0.5 | 0.5 |
| 8×8 ft | 4 in | 0.79 | 0.87 | 40 | 3,200 lb (1.6 tons) | 1 | 1 |
| 10×10 ft | 4 in | 1.23 | 1.36 | 62 | 4,960 lb (2.5 tons) | 1.5 | 1.5 |
| 10×12 ft | 4 in | 1.48 | 1.63 | 74 | 5,920 lb (3.0 tons) | 1.75 | 2 |
| 12×12 ft | 4 in | 1.78 | 1.96 | 88 | 7,040 lb (3.5 tons) | 2 | 2 |
| 12×16 ft | 4 in | 2.37 | 2.61 | 118 | 9,440 lb (4.7 tons) | 2.75 | 3 |
| 16×20 ft | 4 in | 3.95 | 4.35 | 196 | 15,680 lb (7.8 tons) | 4.5 | 4.5 |
| 20×20 ft | 4 in | 4.94 | 5.43 | 245 | 19,600 lb (9.8 tons) | 5.5 | 5.5 |
| 24×24 ft | 4 in | 7.11 | 7.82 | 352 | 28,160 lb (14.1 tons) | 8 | 8 |
| 4×4 ft | 6 in | 0.30 | 0.33 | 15 | 1,200 lb (0.6 tons) | 0.5 | 0.5 |
| 6×6 ft | 6 in | 0.67 | 0.73 | 33 | 2,640 lb (1.3 tons) | 0.75 | 1 |
| 8×8 ft | 6 in | 1.19 | 1.30 | 59 | 4,720 lb (2.4 tons) | 1.5 | 1.5 |
| 10×10 ft | 6 in | 1.85 | 2.04 | 92 | 7,360 lb (3.7 tons) | 2.25 | 2.5 |
| 10×12 ft | 6 in | 2.22 | 2.44 | 110 | 8,800 lb (4.4 tons) | 2.5 | 2.5 |
| 12×12 ft | 6 in | 2.67 | 2.93 | 132 | 10,560 lb (5.3 tons) | 3 | 3 |
| 12×16 ft | 6 in | 3.56 | 3.91 | 176 | 14,080 lb (7.0 tons) | 4 | 4 |
| 16×20 ft | 6 in | 5.93 | 6.52 | 294 | 23,520 lb (11.8 tons) | 6.75 | 7 |
| 20×20 ft | 6 in | 7.41 | 8.15 | 367 | 29,360 lb (14.7 tons) | 8.25 | 8.5 |
| 24×24 ft | 6 in | 10.67 | 11.73 | 528 | 42,240 lb (21.1 tons) | 11.75 | 12 |
Two things the table makes visible: the ordering step matters most on small slabs (a 10×12 ft slab at 4 in needs 1.63 yd³ but a half-yard supplier delivers 2), and the bag count climbs to hundreds of bags well before 10 yd³, which is where labor rather than price usually decides.
How do I turn a price per yard into a price per square foot?
Multiply your price per cubic yard by the thickness in inches and divide by 324 (27 ft³ × 12 in): every $100 per yard costs $1.235 per square foot at 4 in and $1.852 at 6 in, before waste. Use the per-$100 figure to scale any quote; at $150 per yard and 4 in, for example, the concrete is 1.5 × $1.235 = $1.85 per square foot.
| Thickness | Slab area per yd³ | Per ft² per $100/yd³ | With 10% waste | 80 lb bags per ft² |
|---|---|---|---|---|
| 3.5 in | 92.6 ft² | $1.080 | $1.188 | 0.486 bags (0.535 with 10%) |
| 4 in | 81.0 ft² | $1.235 | $1.358 | 0.556 bags (0.611 with 10%) |
| 5 in | 64.8 ft² | $1.543 | $1.698 | 0.694 bags (0.764 with 10%) |
| 6 in | 54.0 ft² | $1.852 | $2.037 | 0.833 bags (0.917 with 10%) |
| 8 in | 40.5 ft² | $2.469 | $2.716 | 1.111 bags (1.222 with 10%) |
The same arithmetic converts the other ways prices are quoted: price per ft³ = price per yd³ ÷ 27, and price per m³ = price per yd³ ÷ 0.7646 (1 yd³ = 0.7646 m³). A quote "per square foot installed" already includes labor and finish, so compare it only with a total that has those in "other costs".
What does one cubic yard of bagged concrete involve?
One cubic yard of bagged concrete is 45 bags of 80 lb mix, 3,600 lb to carry and about 34–51 gallons of mixing water, and the 3,600 lb is the same whichever bag size you choose: every size in Quikrete's sheet weighs about 133 lb per cubic foot of yield, so smaller bags only mean more bags.
| Bag | Yield per bag | Bags per yd³ | Weight per yd³ | Water per yd³ | Area per bag at 4 in | Cost per yd³ |
|---|---|---|---|---|---|---|
| 80 lb | 0.60 ft³ | 45 | 3,600 lb | 33.8–50.6 gal | 1.80 ft² | 45 × your bag price |
| 60 lb | 0.45 ft³ | 60 | 3,600 lb | 30.0–52.5 gal | 1.35 ft² | 60 × your bag price |
| 40 lb | 0.30 ft³ | 90 | 3,600 lb | 33.8–50.6 gal | 0.90 ft² | 90 × your bag price |
That is why the price per bag is the number to compare: 45 × the 80 lb price, 60 × the 60 lb price or 90 × the 40 lb price gives the cost of a yard in bags, directly comparable with a ready-mix quote per yard.
Result looks wrong? Check these
- Truck total jumps for a slightly smaller slab: the order fell below the short-load threshold, so the fee now applies. Enlarging the pour a little or adding a second job to the same truck can be cheaper.
- Break-even says bags are never more expensive: 45 bags (80 lb) cost less than one yard from the truck at your prices, so the fees never get repaid. Check that you entered the price per yard, not per load.
- Break-even says the truck is always cheaper: your bag price times 45 is far above the yard price and fees are small; that is normal where ready-mix is cheap.
- Thickness entered in feet: 0.33 in is not 4 in. Thickness is in inches.
- Per-square-foot figure looks low next to a contractor quote: contractor prices include labor, base, forms and finish. Put those in "other costs" to compare like with like.
When not to use this calculator
- Hiring a contractor for the whole job: the quote you get is the price; use this tool to check the concrete share of it. For driveways see the concrete driveway cost guide.
- Structural slabs (garage, foundation, anything under a building): thickness, reinforcement and mix strength follow your local code and an engineer, not a price comparison.
- Pumped or remote pours: pump rental and waiting time can outweigh everything else; enter them as truck fees, or get an all-in quote.
- Very large slabs: beyond about 40 yd³ the break-even search stops; at that size the truck is the only practical option anyway.
Frequently asked questions
How much does a concrete slab cost?
A concrete slab costs its volume times your local price: a 10×10 ft slab 4 inches thick needs 1.36 cubic yards with 10% waste, which is 62 80 lb bags or a 1.5 yd³ ready-mix order. This calculator uses the prices you enter rather than a national average, because bag prices and truck fees differ by store, supplier and region.
How much does a concrete pad cost?
A concrete pad costs the same way as a slab: an 8×8 ft pad 4 inches thick needs 0.87 yd³ with 10% waste, or 40 80 lb bags, so multiply 40 by your bag price; a 1 yd³ truck order usually carries a short-load fee, which is why small pads are often cheaper in bags.
Is it cheaper to use bags or ready-mix concrete?
Bags are cheaper for small pours and ready-mix is cheaper above a break-even volume: the break-even is roughly your truck's fixed fees divided by (45 × your 80 lb bag price − the ready-mix price per yard). For example, $200 of short-load and delivery fees and a $100-per-yard price gap put the break-even at 2 cubic yards.
How many 80 lb bags of concrete make a yard?
It takes 45 bags of 80 lb concrete mix to make one cubic yard, because each 80 lb bag of Quikrete Concrete Mix yields about 0.60 ft³ and a cubic yard is 27 ft³; with 60 lb bags (0.45 ft³) it takes 60, and with 40 lb bags (0.30 ft³) it takes 90.
How do I convert concrete price per yard to price per square foot?
Multiply the price per cubic yard by the slab thickness in inches and divide by 324: at 4 inches, every $100 per cubic yard is $1.235 per square foot of slab before waste, or $1.358 with 10% waste. At 6 inches the same $100 is $1.852 per square foot.
What is a short-load fee on ready-mix concrete?
A short-load fee is an extra charge some ready-mix suppliers add when an order is below their minimum full-load volume, so a small truck order can cost much more per yard than the quoted price. Ask for the threshold and the fee, enter both above, and the calculator adds the fee only when your order is under the threshold.
How much concrete should I order for a slab?
Order the slab volume plus a waste allowance of about 5–10%, rounded up to your supplier's ordering step: a 12×16 ft slab at 4 inches is 2.37 yd³, 2.61 yd³ with 10% waste, so a supplier that sells in quarter yards would deliver 2.75 yd³.
Does this calculator include labor and finishing?
No, it prices the concrete itself; labor, forms, gravel base, rebar or mesh, finishing and permits go in the optional ‘other costs’ field, which is added to both the bag and the truck total so the comparison stays fair.
Sources
- Quikrete, Concrete Mix No. 1101 data sheet (rev. October 2022): yields 0.30 / 0.45 / 0.60 ft³ for 40 / 60 / 80 lb bags; Table 2 mixing water (retrieved 2026-10-15).
- The Home Depot, Quikrete 80 lb Concrete Mix product page (retrieved 2026-10-20): "45-bags equal 1-cubic yard"; prices vary by store and are not used here.
- NIST, 1 yd³ = 27 ft³ = 0.764555 m³ (NIST Handbook 44, Appendix C, 2024); used for all unit conversions.
- Volume function:
Calcs.concreteSlabin js/calcs.js, the same code as the concrete slab calculator.
Related calculators & guides
- Concrete slab volume in yards and meters
- How many bags of concrete you need
- Concrete pad volume worksheet
- Concrete driveway yards and cost
- Quikrete bag counts by product
- 4-inch vs 6-inch slab
- When the new slab can take traffic
Last updated 2026-10-20 · About TrueToolCalc and how we check numbers · Found an error? Use the contact page.