Calculate concrete volume and bags for slabs, footings, columns or steps. Compare bag and ready-mix quotes with delivery fees, minimums and order increments.
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The pour is 0.944 m³ (1.23 yd³); with 5% extra, plan for 0.991 m³ (1.3 yd³). That is 59 premix bags of 80 lb.
Rounded up to whole bags. Yield per 80 lb bag from Quikrete/Sakrete data sheets.
Volume is length × width × thickness for a slab or footing, πr²h for a round column, and width × run × rise × n(n + 1)/2 for a flight of n solid steps, because the kth step is k risers tall. The volume is given in cubic yards (27 ft³ each) and cubic metres for ordering ready-mix. For bagged premix it is divided by the bag yield; for a site mix it is multiplied by 1.54 and split by the cement : sand : aggregate ratio.
The default 10 × 10 ft slab, 4 in thick, is 33.33 ft³ or 1.23 yd³. With 5% extra it takes 59 bags of 80 lb premix at the 0.60 ft³ yield on Quikrete's data sheet.
Choose Compare quotes to price whole bags against delivered ready-mix. Enter your supplier's prices, order increment, delivery minimum and any billed minimum. The comparison separates material arriving on site from material charged, includes the fees you enter, and reports surplus beyond the volume with extra. No market prices are assumed.
The 1.54 dry-volume factor and the 1,440 kg/m³ bulk density used for cement bags are site-estimating conventions, not a mix design. Structural concrete needs a specified strength from a supplier or engineer.
Multiply length × width × thickness, all in feet, and divide by 27 for cubic yards. Add 5–10% for spillage and uneven ground. For bagged mix, divide the cubic feet by the bag's yield, 0.60 ft³ for an 80 lb bag, and round up. A 10 × 10 ft slab 4 in thick is 1.23 yd³, or 59 bags with 5% extra.
The same rule covers slabs and strip footings; in metric, multiply in meters for cubic meters. Round columns, tube forms and steps have their own formulas below.
This chart holds the slab at 10 × 10 ft and uses 80 lb bags at 0.60 ft³ each, rounded up to whole bags. Extra is the spillage allowance.
| Thickness, in | Extra | Pour, yd³ | With extra, yd³ | 80 lb bags |
|---|---|---|---|---|
| 3.5 | 0% | 1.080 | 1.080 | 49 |
| 3.5 | 5% | 1.080 | 1.134 | 52 |
| 3.5 | 10% | 1.080 | 1.188 | 54 |
| 4 | 0% | 1.235 | 1.235 | 56 |
| 4 | 5% | 1.235 | 1.296 | 59 |
| 4 | 10% | 1.235 | 1.358 | 62 |
| 6 | 0% | 1.852 | 1.852 | 84 |
| 6 | 5% | 1.852 | 1.944 | 88 |
| 6 | 10% | 1.852 | 2.037 | 92 |
| 8 | 0% | 2.469 | 2.469 | 112 |
| 8 | 5% | 2.469 | 2.593 | 117 |
| 8 | 10% | 2.469 | 2.716 | 123 |
Thickness moves the order far more than the allowance: going from 4 to 6 in raises the bags by half, from 56 to 84, while 5% extra at 4 in adds 3 bags.
A 12 × 16 ft patio, 4 in thick, with 5% extra:
Metric. A 5 × 4 m slab 100 mm thick is 5 × 4 × 0.1 = 2 m³, or 2.1 m³ with 5% extra. That is 74.16 ft³, and at 0.413 ft³ per 25 kg bag it takes 180 bags.
Footing. A strip footing for a garden wall, 24 ft long, 16 in wide and 8 in deep, is 24 × 1.3333 × 0.6667 = 21.33 ft³ (0.79 yd³). With 5% extra that is 22.4 ft³, or 38 bags of 80 lb.
Footing sizes for a house are set by the building code or an engineer; the arithmetic only turns a given size into an order.
A cubic yard is 3 × 3 × 3 ft = 27 ft³. Because the yard is exactly 0.9144 m, it is exactly 0.764554857984 m³, and one cubic meter is 1.308 yd³ or 35.31 ft³.
Thickness decides how far a yard goes. One cubic yard covers 324 ÷ thickness in inches, in square feet:
| Slab thickness | Area covered by 1 yd³ |
|---|---|
| 3½ in | 92.57 ft² |
| 4 in | 81 ft² |
| 5 in | 64.8 ft² |
| 6 in | 54 ft² |
| 8 in | 40.5 ft² |
In metric, 1 m³ covers 10 m² at 100 mm, 8 m² at 125 mm, 6.67 m² at 150 mm and 5 m² at 200 mm.
2021 IRC R506.1 sets 3½ in as the minimum for a concrete slab-on-ground floor. That is also the depth of a 2×4 form set on edge.
The American Softwood Lumber Standard, PS 20-25 sets the dry dressed width of a nominal 4 in board at 3½ in, and of a nominal 6 in board at 5½ in. Using 4 in for a slab poured level with 2×4 forms overestimates the concrete by 14.3%.
At a true 3½ in, the 12 × 16 ft patio is 56 ft³ (2.07 yd³), or 98 bags with 5% extra instead of 112.
The Quikrete Concrete Mix data sheet (revised October 2022) gives yields of 0.30 ft³ (8.5 L) for a 40 lb bag, 0.45 ft³ (12.7 L) for 60 lb and 0.60 ft³ (17 L) for 80 lb.
Metric bags scale Quikrete's 0.0075 ft³ per pound of dry mix, so a 25 kg bag yields about 0.413 ft³ (11.7 L).
The Sakrete High-Strength Concrete Mix data sheet prints the same 0.30, 0.45 and 0.60 ft³, and 0.41 ft³ for its 25 kg bag sold in Canada.
| Volume | 40 lb bags | 60 lb bags | 80 lb bags | 25 kg bags |
|---|---|---|---|---|
| 1 ft³ | 4 | 3 | 2 | 3 |
| ½ yd³ (13.5 ft³) | 45 | 30 | 23 | 33 |
| 1 yd³ (27 ft³) | 90 | 60 | 45 | 66 |
| 1 m³ (35.31 ft³) | 118 | 79 | 59 | 86 |
| Round column 12 in across, 4 ft tall (3.14 ft³) | 11 | 7 | 6 | 8 |
Each figure is the volume divided by the yield and rounded up to a whole bag, with no extra allowance. Yields vary by product: Sakrete lists 0.66 ft³ for its 90 lb bag where Quikrete lists 0.675 ft³, so check the bag you buy.
Weight is the other limit. One cubic yard in 80 lb bags is 45 bags, or 3,600 lb of dry mix to lift, mix and place, so once a pour passes about 1 m³ (1.31 yd³), price a ready-mix delivery as well.
Bag cost is whole bags × price per bag, plus any delivery or mixer hire. Ready-mix cost is the billed volume × the price per cubic yard or cubic meter, plus delivery and other fees. Price both in the same currency and on the same tax basis.
Three supplier terms change the ready-mix bill:
Duke City Redi-Mix publishes a one-yard minimum, quarter-yard increments and a separate charge for loads below five yards. Miller's residential ordering page describes a 1 m³ minimum, 0.25 m³ increments and a minimum-load charge below 4 m³.
A short-load fee is a charge, not a requirement to buy the threshold volume, so use the terms in your own quote. For the 10 × 10 ft slab with 5% extra, 35 ft³ or about 1.2963 yd³, these hypothetical prices compare as follows:
| Option | Quantity and price | Other fees | Total |
|---|---|---|---|
| 80 lb bags | 59 × 7 | 40 | 453 |
| Ready-mix in 0.25 yd³ increments | 1.5 yd³ × 180 | 150 | 420 |
| Same delivery with a 3 yd³ billing minimum | 3 yd³ billed × 180 | 150 | 690 |
The ordinary delivery saves 33; the billing minimum makes bags cheaper by 237. Both ready-mix rows deliver 1.5 yd³, about 0.2037 yd³ beyond the volume with the allowance, while the 59 bags make 35.4 ft³, 0.4 ft³ beyond it.
A 3 yd³ delivered minimum, unlike a billing minimum, would bring 1.7037 yd³ of surplus to the site.
Totals cover only the prices and fees you include, so add labor, pumping and taxes to both sides if they apply, and confirm both quotes supply the mix the job needs.
A round column or tube form is a cylinder: π × radius² × height, where the radius is half the diameter. Using the diameter as the radius gives four times the real volume.
Six deck piers poured in 10 in tube forms, 42 in deep:
That rounds up once, on the total. If each hole is mixed and filled from its own bags, each pier needs 3.34 bags, which becomes 4, and the job takes 24 bags. Buy for the way you will mix.
A flight of n solid steps holds width × run × rise × n(n + 1) ÷ 2, because the kth step is k risers tall. Four steps 4 ft wide with 7 in risers and 11 in treads hold 4 × 0.9167 × 0.5833 × 10 = 21.39 ft³: 36 bags of 80 lb.
Estimating steps as one box overstates them. A box four risers high and four treads deep holds 16 riser-by-tread blocks, but four solid steps hold 1 + 2 + 3 + 4 = 10: the box is 60% too much. Get the rise and run from the stair calculator.
Dry ingredients take about 1.54 times the finished volume, because the gaps between grains fill with paste. Split that by the ratio: 1 m³ of a 1:2:4 mix needs 1.54 ÷ 7 = 0.22 m³ of cement, 0.44 m³ of sand and 0.88 m³ of aggregate.
At a bulk density of 1,440 kg/m³, a 50 kg bag of cement is 0.0347 m³, so 0.22 m³ is 6.34 bags, bought as 7. A 1:1.5:3 mix needs 8.06 bags per m³ and 1:3:6 needs 4.44.
The 1.54 factor and the bulk density are site-estimating conventions, not a mix design. Structural concrete needs a specified strength from a supplier or engineer.
Allow 5–10% for site work. The allowance covers spillage, forms that bow outward and ground below the planned level, and uneven ground can outweigh the rest because the error is a fraction of a small thickness.
If the base under a 4 in slab averages ¼ in low, the slab needs 6.25% more concrete; at ½ in low, 12.5% more. Leveling and compacting the base reduces the allowance you need, and the gravel calculator sizes the stone for it.
Running short costs more than a few spare bags. Quikrete's data sheet tells users to fill forms to full depth and avoid partial-depth fills, which can leave cold joints.
To convert a result into liters, cubic feet or other units, use the volume converter.
Checked against: 10 × 10 × 4/12 = 33.33 ft³ = 1.2346 yd³; ÷ 0.60 ft³ per 80 lb bag (Quikrete TDS) = 55.6 → 56
Checked against: Hypothetical quotes; 1.5 yd³ × 180 + 150 = 420.
Checked against: Independent calculation
Checked against: Hypothetical quotes; 53 × 9 + 20 = 497 versus 1.25 × 180 + 40 = 265.
Divide the volume in cubic feet by the bag yield and round up. Quikrete's Concrete Mix data sheet gives 0.60 ft³ per 80 lb bag, 0.45 ft³ per 60 lb and 0.30 ft³ per 40 lb. A 10 × 10 ft slab 4 in thick is 33.33 ft³: 56 bags of 80 lb, or 59 with 5% extra. One cubic yard (27 ft³) takes 45 bags of 80 lb.
Multiply length × width × thickness in feet and divide by 27. A 10 × 10 ft slab 4 in (0.333 ft) thick is 33.33 ft³ ÷ 27 = 1.23 yd³; at 6 in thick it is 1.85 yd³. Ready-mix is ordered by the cubic yard in the US and by the cubic metre elsewhere; 1 yd³ = 0.7646 m³.
At least 3½ in for a residential slab-on-ground floor under 2021 IRC R506.1. A 2×4 set on edge as a form is 3½ in deep (its dressed size under the American Softwood Lumber Standard, PS 20), so a slab poured to 2×4 forms meets that minimum. Thickness drives volume directly: going from 4 to 6 in on a 10 × 10 ft slab raises the concrete from 1.23 to 1.85 yd³, and the 80 lb bag count from 56 to 84.
For a 1:2:4 nominal mix, the site rule multiplies the wet volume by 1.54 for dry materials: 1.54 ÷ 7 = 0.22 m³ of cement, 0.44 m³ of sand and 0.88 m³ of aggregate. At 1,440 kg/m³ that is 6.34 bags of 50 kg cement, bought as 7. A 1:1.5:3 mix needs 8.06 bags per m³ and 1:3:6 needs 4.44.
It depends on your quotes and the quantity purchased. In Compare quotes, bag cost is whole bags × price per bag + bag extras. Ready-mix cost is billed volume × price per cubic yard or metre + delivery and other fees. Enter the same currency and tax basis for both. Positive Savings with ready-mix means delivery costs less; a negative result means bags cost less. Labor, equipment, pumping and taxes count only if you include them in your prices or extras.
A minimum delivered volume can create surplus concrete. A minimum billed volume raises the charge without increasing the delivery. An order increment rounds the delivered volume up to a multiple of that increment. Enter a quoted short-load charge in Ready-mix delivery and other fees; the calculator does not infer a supplier's policy. Surplus is measured beyond the pour volume plus your extra allowance.
This calculator includes 8 worked examples with independently sourced answers. They run in the test suite, and you can run them here too.