Concrete Calculator
Free online concrete calculator for slabs, patios, and pads. Enter length, width, and thickness to get cubic yards, a ready-mix order, and bag counts.
- Free, no signup
- Formula shown
- Rounds up to whole units
- Updated October 2026
Concrete needed · 10% allowance
1.36cubic yards
Ready-mix order
1.5 yd³
¼ cubic yard steps
80 lb bags
62 bags
0.6 ft³ each
- Before allowance
- 1.23 yd³
- Cubic feet
- 36.7 ft³
- Cubic meters
- 1.04 m³
Bag count uses the yield published for 80 lb QUIKRETE Concrete Mix (No. 1101).
AnswerA 10 ft × 10 ft slab 4 in thick needs 1.23 cubic yards of concrete (1.36 with a 10% allowance): order 1.5 cubic yards of ready-mix in ¼ cubic yard steps, or 62 80 lb QUIKRETE Concrete Mix (No. 1101) bags.
Bag counts for every documented product
| Product | Bag | Published yield | Bags to buy |
|---|---|---|---|
| QUIKRETE Concrete Mix (No. 1101) | 80 lb | 0.6 ft³ | 62 |
| QUIKRETE Concrete Mix (No. 1101) | 60 lb | 0.45 ft³ | 82 |
| QUIKRETE Concrete Mix (No. 1101) | 40 lb | 0.3 ft³ | 123 |
| QUIKRETE Concrete Mix (No. 1101) (regional availability) | 90 lb | 0.675 ft³ | 55 |
| QUIKRETE 5000 Concrete Mix (No. 1007) | 80 lb | 0.6 ft³ | 62 |
| QUIKRETE 5000 Concrete Mix (No. 1007) | 60 lb | 0.45 ft³ | 82 |
| QUIKRETE Fast-Setting Concrete Mix (No. 1004) | 50 lb | 0.375 ft³ | 98 |
| Sakrete High-Strength Concrete Mix | 80 lb | 0.6 ft³ | 62 |
| Sakrete High-Strength Concrete Mix | 60 lb | 0.45 ft³ | 82 |
| Sakrete High-Strength Concrete Mix | 40 lb | 0.3 ft³ | 123 |
| Sakrete High-Strength Concrete Mix | 90 lb | 0.66 ft³ | 56 |
How to use this concrete calculator
- Choose feet or meters, then enter the slab's length and width. Measure inside the forms, not the outside of the boards.
- Enter the thickness in inches or centimeters. Measure the actual form height: nominal lumber is smaller than its name (the softwood lumber standard lists a nominal 6 in width at 5-1/2 in dressed).
- Set a waste allowance. The default 10% is an adjustable planning figure, not a standard. Use more if the subgrade is uneven or the measurements are rough.
- Pick the increment your ready-mix supplier sells in, and the bagged product you plan to buy. The bag count uses that product's published yield.
- For an L-shaped or irregular slab, split it into rectangles, run each one, and add the results. See measuring irregular areas.
How to calculate concrete: the formula, shown
Concrete is ordered by volume. A rectangular slab is length × width × thickness, with every dimension converted to the same unit first. One cubic yard is 3 ft × 3 ft × 3 ft = 27 cubic feet, and one foot is exactly 0.3048 m, so one cubic yard is 0.764555 m³.
Default example. A 10 ft × 10 ft slab, 4 in thick, with a 10% allowance. Change the inputs above and the result panel recalculates; this worked example always shows the default.
Area = 10 ft × 10 ft = 100 ft² Thickness = 4 in ÷ 12 in/ft = 0.3333 ft Volume = 100 ft² × 0.3333 ft = 33.3333 ft³ Cubic yards = 33.3333 ft³ ÷ 27 = 1.2346 yd³ Allowance = 1.2346 yd³ × (1 + 10/100) = 1.358 yd³ (36.6667 ft³) Metric = 36.6667 ft³ × 0.3048³ = 1.0383 m³ Ready-mix = 1.358 ÷ 0.25 = 5.432 → 6 steps = 1.5 yd³ Bags = 36.6667 ft³ ÷ 0.6 ft³/bag = 61.11 → 62 bags (80 lb)
Two numbers are kept separate on purpose: the requirement (1.36 yd³) carries full precision, and the purchase quantity rounds that requirement up to whole supplier steps or whole bags. Rounding happens only once, at the end, and only upward.
How much concrete for common slab sizes
Cubic yards of concrete for common square slabs at 4 in and 6 in thick, computed with the same formula as the calculator. Figures have no waste allowance, so add yours before ordering. Bag counts use the 0.60 ft³ yield published for 80 lb QUIKRETE Concrete Mix (No. 1101), rounded up to whole bags.
| Slab size | 4 in: cubic yards | 4 in: 80 lb bags | 6 in: cubic yards | 6 in: 80 lb bags |
|---|---|---|---|---|
| 4 × 4 ft | 0.2 | 9 | 0.3 | 14 |
| 10 × 10 ft | 1.23 | 56 | 1.85 | 84 |
| 12 × 12 ft | 1.78 | 80 | 2.67 | 120 |
| 16 × 16 ft | 3.16 | 143 | 4.74 | 214 |
| 20 × 20 ft | 4.94 | 223 | 7.41 | 334 |
| 24 × 24 ft | 7.11 | 320 | 10.7 | 480 |
| 30 × 30 ft | 11.1 | 500 | 16.7 | 750 |
How much concrete to order: ready-mix or bags
For the default 10 × 10 ft slab, the requirement is 1.36 cubic yards. In ¼ cubic yard steps that becomes a ready-mix order of 1.5 yd³. In bags, it is 62 bags of 80 lb QUIKRETE Concrete Mix (No. 1101).
- Ready-mix truck: give the supplier the rounded-up volume and ask about minimum loads, short-load charges, and how long the truck can wait. These vary by supplier.
- Bagged mix: buy the whole-bag count for the exact product on your receipt. Yields differ between products and bag sizes. A 90 lb bag is listed at 0.675 ft³ by QUIKRETE and 0.66 ft³ by Sakrete. See concrete bag yields.
- Choosing between them: the bagged vs bulk guide walks through the trade-offs, including labor and mixing time.
Concrete bag calculator: QUIKRETE and Sakrete yields
A bag count depends on the yield the manufacturer publishes for that product, not on its weight alone. These are the yields used above:
| Product | Bag | Yield per bag | Bags per cubic yard |
|---|---|---|---|
| QUIKRETE Concrete Mix (No. 1101) | 80 lb | 0.6 ft³ | 45 |
| QUIKRETE Concrete Mix (No. 1101) | 60 lb | 0.45 ft³ | 60 |
| QUIKRETE 5000 Concrete Mix (No. 1007) | 80 lb | 0.6 ft³ | 45 |
| QUIKRETE 5000 Concrete Mix (No. 1007) | 60 lb | 0.45 ft³ | 60 |
| Sakrete High-Strength Concrete Mix | 80 lb | 0.6 ft³ | 45 |
| Sakrete High-Strength Concrete Mix | 60 lb | 0.45 ft³ | 60 |
Bags per cubic yard = 27 ft³ ÷ yield, before rounding up and before allowance. More products and bag sizes are in concrete bag yields.
QUIKRETE calculator
Choose a QUIKRETE product in the Bagged product menu to count bags with its published yield: Concrete Mix (No. 1101), 5000 Concrete Mix (No. 1007), or Fast-Setting Concrete Mix (No. 1004).
Concrete yard calculator: ordering by the cubic yard
Ready-mix is sold by volume. The result panel rounds your requirement up to the increment you choose, from ¼ cubic yard to 1 cubic meter, so you can give the supplier a number they can load.
Tips for measuring a concrete slab
- Measure thickness in several places. A slab planned at 4 in that averages 4.5 in needs 12.5% more concrete.
- Run the numbers in your supplier's unit. If they quote cubic meters, set the increment to a cubic-meter step.
- A gravel base under the slab is a separate material. Size it with the gravel calculator.
- Count bags against the yield printed on the bag you actually buy. Bags sold in other regions may be different sizes.
- This calculator measures volume only. Thickness, reinforcement, and base requirements come from your plans or local building authority.
Concrete calculator FAQ
How much concrete do I need for a 10x10 slab 4 inches thick?
A 10 ft × 10 ft slab 4 in thick is 33.3 cubic feet, or 1.23 cubic yards, before any allowance. With a 10% allowance it is 1.36 cubic yards. That rounds up to 1.5 yd³ of ready-mix in quarter-yard steps, or 62 80 lb bags of QUIKRETE Concrete Mix.
How many bags of concrete are in a cubic yard?
It depends on the product's published yield. QUIKRETE lists its Concrete Mix (No. 1101) at 0.6 ft³ per 80 lb bag, 0.45 ft³ per 60 lb bag, and 0.3 ft³ per 40 lb bag. A cubic yard is 27 ft³, so that works out to 45, 60, and 90 bags per cubic yard before any allowance.
How do I convert cubic feet of concrete to cubic yards?
Divide cubic feet by 27. A cubic yard is 3 ft × 3 ft × 3 ft, which is 27 cubic feet. For example, 54 cubic feet is 2 cubic yards.
Do all concrete bags of the same weight yield the same volume?
No. The 80 lb QUIKRETE and Sakrete mixes listed here are each published at 0.60 ft³, but other sizes and products differ. QUIKRETE lists its 90 lb Concrete Mix at 0.675 ft³, while Sakrete lists its 90 lb High-Strength Concrete Mix at 0.66 ft³. QUIKRETE Fast-Setting Concrete Mix is 0.375 ft³ per 50 lb bag. Use the yield printed on the bag you buy.
How much extra concrete should I order?
No single figure fits every job. This calculator defaults to a 10% allowance as an adjustable example. Raise it if the subgrade is uneven, the forms are long, or your measurements are rough. Lower it for small, well-formed pours you have measured carefully. The allowance is applied before rounding up to bags or supplier steps.
Why does the ready-mix order differ from the cubic yards I need?
Suppliers sell in fixed increments. The calculator rounds your requirement up to whole steps of the increment you choose. Rounding is never down, so a 1.36 yd³ requirement becomes 1.5 yd³ in quarter-yard steps.
Can I enter metric measurements?
Yes. Switch length and width to meters and thickness to centimeters. The result is always shown in cubic feet, cubic yards, and cubic meters. You can also choose a cubic-meter order increment if your supplier sells by the cubic meter.
How do I calculate concrete for a round or L-shaped slab?
Split an L-shaped slab into rectangles, calculate each one, and add the volumes. For a circle, area is π × radius², and volume is that area times thickness. The guide to measuring irregular areas shows how to break shapes down.
Does the result include a gravel base, rebar, or footings?
No. The calculator estimates the volume of a flat rectangular slab of uniform thickness. Base material, thickened edges, footings, and reinforcement depend on your design and local requirements. Calculate them separately.
Related calculators and guides
Calculators
- Gravel Calculator — Gravel, crushed rock, or landscape rock volume in cubic yards and meters, with an optional weight from your supplier's density.
- Topsoil Calculator — Topsoil volume in cubic yards and meters for lawns, beds, and fill, with an optional weight from your supplier's density.
- Deck Calculator — Decking board count from deck size, actual board width, gap, and board length, with the cutting assumptions shown.
Guides
- Concrete Bag Yields by Bag Size — Published cubic-foot yields for bagged concrete mixes, with bags per cubic foot, cubic yard, and cubic meter.
- What Is a Cubic Yard? — What a cubic yard is, how to convert area × depth into yards, and how much ground one yard covers.
- Bagged vs. Bulk Materials: Which Should You Buy? — How to compare bags and bulk delivery using bags per cubic yard and your own local prices.
- How to Plan a Bulk Material Delivery — Rounding to supplier increments, questions to ask, and a checklist before bulk material arrives.
Sources
- QUIKRETE Concrete Mix (No. 1101) product data sheet — QUIKRETE Companies. Used for: 40 lb = 0.30 ft³; 60 lb = 0.45 ft³; 80 lb = 0.60 ft³; 90 lb = 0.675 ft³ (regional). Checked 2026-10-03.
- QUIKRETE 5000 Concrete Mix (No. 1007) product data sheet — QUIKRETE Companies. Used for: 60 lb = 0.45 ft³; 80 lb = 0.60 ft³. Checked 2026-10-03.
- QUIKRETE Fast-Setting Concrete Mix (No. 1004) product data sheet — QUIKRETE Companies. Used for: 50 lb = 0.375 ft³. Checked 2026-10-03.
- Sakrete High-Strength Concrete Mix technical data sheet — Sakrete. Used for: 40 lb = 0.30 ft³; 60 lb = 0.45 ft³; 80 lb = 0.6 ft³; 90 lb = 0.66 ft³. Checked 2026-10-03.
- NIST Guide to the SI, Appendix B.9: Factors for units listed by kind of quantity — National Institute of Standards and Technology. Used for: 1 ft = 0.3048 m (exact); 1 in = 2.54 cm (exact). Checked 2026-10-03.
- NIST Handbook 44 (2026), Appendix C: General Tables of Units of Measurement — National Institute of Standards and Technology. Used for: 1 yd³ = 27 ft³; 1 US gal = 231 in³. Checked 2026-10-03.