Calculate concrete volume and bags for slabs, footings, columns or steps. Compare bag and ready-mix quotes with delivery fees, minimums and order increments.
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.
Put every dimension in the same unit before multiplying. In US units that means feet, so divide inches by 12; in metric, metres, so divide millimetres by 1,000. Then multiply length × width × thickness, add the extra allowance, and divide by the yield of one bag.
A 12 × 16 ft patio, 4 in thick, with the calculator's default 5 % extra:
The metric version works the same way. 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.
Footings use the same length × width × depth formula. 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, not by the calculator.
A cubic yard is 3 × 3 × 3 ft = 27 ft³, and because the yard is exactly 0.9144 m, it is exactly 0.764554857984 m³. One cubic metre is 1.308 yd³ or 35.31 ft³.
Thickness decides how far a yard goes. The area one cubic yard covers is 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.
The 3½ in row matters because 2021 IRC R506.1 sets 3½ in as the minimum for a concrete slab-on-ground floor, and forms built from 2×4s set on edge are that deep: 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. Entering 4 in for a slab poured level with 2×4 forms overestimates the concrete by 14.3 %. The 12 × 16 ft patio at a true 3½ in is 56 ft³ (2.07 yd³), or 98 bags with 5 % extra instead of 112.
The calculator's bag yields come from the Quikrete Concrete Mix data sheet (revised October 2022): 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. For metric bags it scales Quikrete's 0.0075 ft³ per pound of dry mix, giving 0.413 ft³ (11.7 L) for 25 kg. 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. Check the yield printed on 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. Once a pour passes 1 m³ (1.31 yd³), the calculator suggests pricing a ready-mix delivery.
Choose Compare quotes under Materials. Enter a price per bag and a ready-mix price per cubic yard or cubic metre, using the same currency and tax basis. Prices start blank; the calculator shows a known option's total but waits for both prices before comparing them. A price of zero is allowed if that material really costs you nothing. Changing the ready-mix price unit changes the meaning of the number entered; it does not convert the price.
Bag cost uses the whole number of bags you will buy. Choose Yield from my bag when your product's stated yield differs from the preset, and enter its finished volume in litres, cubic feet or cubic metres. Metric presets are estimates scaled by weight, so a quoted product's printed yield is a better basis for purchasing.
For ready-mix, enter the supplier's terms separately:
These terms differ by supplier. For example, 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 not automatically a requirement to buy that threshold volume. Use the terms in your quote.
Consider the default 10 × 10 ft slab, 4 in thick, with 5% extra: it needs 35 ft³, or about 1.2963 yd³. The following prices are hypothetical examples, not current market quotes:
| 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, leaving about 0.2037 yd³ beyond the volume with the allowance. Changing the delivered minimum to 3 yd³ would instead produce about 1.7037 yd³ of surplus. The bag option provides 35.4 ft³, leaving 0.4 ft³ beyond the allowance.
Savings with ready-mix is bag total minus ready-mix total. Positive means ready-mix costs less; negative means bags cost less. Totals include only the prices and fees entered. Include labor, equipment, pumping and taxes consistently if you want them compared. Confirm that both quotes supply the required mix, since price alone does not establish suitability.
A round column or tube form is a cylinder: π × radius² × height. The calculator asks for the diameter and halves it. Using the diameter as the radius gives four times the real volume.
Six deck piers poured in 10 in tube forms, 42 in deep:
The calculator 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.
The calculator adds 5 % by default and suggests 5–10 % for site work. The allowance covers spillage, forms that bow outward and ground that sits below the planned level. Uneven ground can outweigh the others on a slab, 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, and at ½ in low, 12.5 % more. Levelling and compacting the base to the planned depth reduces the allowance you need; 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.
Three arithmetic errors are worth checking for:
To convert a result into litres, cubic feet or other units, use the volume converter.
Checked against: Python decimal: 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; independent Python Fraction fixture: 35 ft³ with allowance → 59 bags × 7 + 40 = 453; 1.5 yd³ × 180 + 150 = 420.
Checked against: Hypothetical quotes; independent Python Fraction fixture: 3 yd³ billed × 180 + 150 = 690, but only 1.5 yd³ delivered. Bags cost 237 less.
Checked against: Hypothetical quotes; independent Python Fraction fixture: 1.05 m³ ÷ 0.02 m³ → 53 bags; 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.
Accuracy depends on your inputs and the method's assumptions. Decimal arithmetic uses 50 significant digits, but estimates, numerical methods and source data can be less precise; the displayed rounding does not remove those limits. It is checked against 8 worked examples whose answers come from independent sources; for example, “10 × 10 ft slab, 4 in thick, 80 lb bags” is checked against Python decimal: 10 × 10 × 4/12 = 33.33 ft³ = 1.2346 yd³; ÷ 0.60 ft³ per 80 lb bag (Quikrete TDS) = 55.6 → 56.
Quikrete Concrete Mix (No. 1101) data sheet — bag yields: 40 lb 0.30 ft³, 60 lb 0.45 ft³, 80 lb 0.60 ft³; Duke City Redi-Mix — example of a supplier's minimum order and quarter-yard increments; The Miller Group — residential concrete ordering and minimum-load charges; International Code Council — 2021 IRC R506.1: concrete slab-on-ground floors at least 3½ in thick; Civil Practical Knowledge — dry volume factor 1.54 for concrete (rule of thumb).
8 worked examples with independently sourced answers ship with this calculator. They run in the test suite; you can run them here too.
Gravel calculator: cubic metres, cubic yards, tonnes, bags and truck loads of gravel, sand, topsoil or mulch for an area and depth.
Fence calculator: posts, rails, pickets and bags of concrete for a straight fence run, from its length, post spacing, picket width and gap.
Number of steps, riser height, tread depth, stringer length and stair angle from total rise and run, checked against IRC riser and tread limits.
Brick calculator: bricks or blocks for a wall from its size, openings, unit size and joint, with count per m² or ft², mortar volume and waste.
Roof area, squares and shingle bundles from building size and pitch, with underlayment rolls, ridge cap and the IRC minimum slope check.
Allow optional Google Analytics to measure page visits? Calculators work either way. Privacy and choices
Optional analytics: off.