Concrete Calculator
Concrete Calculator
Enter your length, width and depth, pick a unit, and this concrete calculator returns the volume in cubic yards and cubic meters, the number of 40, 60 and 80 pound bags, the weight, and a price estimate. It covers slabs, footings, columns, walls and tube forms, so one tool answers the question most people start with: how much concrete do I need.
A short pour is the costly mistake on any job. If the truck leaves and you come up a quarter yard short, you get a cold joint and a second delivery fee. Order too much and you pay for concrete that becomes spoil. A quick estimate before you order keeps the pour on budget and on schedule.
How this concrete calculator works
The math behind every result is simple. For a rectangular pour, volume equals length times width times thickness, with all three measurements in the same unit. The tool converts your inches, feet or meters for you, then reports the answer in the units suppliers actually sell.
Two numbers do most of the work. One cubic yard equals 27 cubic feet, and normal weight concrete weighs about 150 pounds per cubic foot, so a full yard weighs close to 4,050 pounds, just over two tons. Ready mix in the United States is ordered by the cubic yard. Most of the rest of the world orders by the cubic meter, and one cubic meter is about 1.31 cubic yards.
Formulas for every shape
Real projects are rarely one flat rectangle. The table lists the formula for each shape this tool supports, with a worked figure you can check by hand.
| Shape | Formula | Worked example |
|---|---|---|
| Slab or wall | Length × Width × Thickness | 10 ft × 10 ft × 4 in = 1.23 cu yd |
| Footing (strip) | Length × Width × Depth | 40 ft × 1.5 ft × 1 ft = 2.22 cu yd |
| Square column | Width × Depth × Height | 1 ft × 1 ft × 10 ft = 0.37 cu yd |
| Round column or tube | 3.1416 × radius² × Height | 12 in wide × 10 ft = 0.29 cu yd |
| Circular pad | 3.1416 × radius² × Thickness | 10 ft wide × 4 in = 0.97 cu yd |
The one rule that trips people up is unit discipline. Every dimension has to be in the same unit before you multiply. Thickness is the usual culprit, because slabs are quoted in inches while length and width are in feet. Convert the inches to feet first (divide by 12), or let the tool handle it.
Worked example, a 10 by 10 slab
Say you are pouring a 10 foot by 10 foot patio at 4 inches thick. Convert the thickness: 4 inches divided by 12 is 0.333 feet. Multiply the three figures: 10 × 10 × 0.333 equals 33.3 cubic feet. Divide by 27 and you get 1.23 cubic yards. Add 10 percent for waste and you would order about 1.35 yards, which in practice means a 1.5 yard minimum from most plants. Poured from bags instead, 33.3 cubic feet at 0.60 cubic feet per 80 pound bag is about 56 bags, which is the point where a ready mix delivery starts to make more sense than mixing by hand.
Bags or ready mix, and how many bags per yard
Each bag of concrete yields a fixed volume of wet mix, so the bag count is your total cubic feet divided by the yield per bag. The figures below come from the Quikrete Concrete Mix data sheet and match Sakrete and most store brands, since standard bags share the same yield by weight.
| Bag size | Yield per bag | Bags per cubic yard |
|---|---|---|
| 40 lb | 0.30 cu ft | 90 |
| 50 lb | 0.375 cu ft | 72 |
| 60 lb | 0.45 cu ft | 60 |
| 80 lb | 0.60 cu ft | 45 |
The practical crossover is around one cubic yard. Below that, bags usually win on cost and convenience. Above two yards you are mixing 90 or more bags by hand, so a truck is cheaper and gives a more consistent pour.
How much concrete weighs
Standard concrete weighs roughly 150 pounds per cubic foot. Multiply by 27 and a single cubic yard is about 4,050 pounds. That figure sets form pressure, what a trailer can legally haul, and what the ground below has to carry. Reinforced concrete runs a little heavier, near 156 pounds per cubic foot, while lightweight structural mixes drop to around 110.
Choosing the right thickness
Thickness drives both your volume and your cost, so match it to the load rather than guess.
| Use | Typical thickness | Common strength |
|---|---|---|
| Walkway, patio, shed pad | 4 in | 3,000 to 3,500 psi |
| Residential driveway | 4 to 5 in | 3,500 to 4,000 psi |
| Garage or shop floor | 5 to 6 in | 4,000 psi |
| Light commercial floor | 6 to 8 in | 4,000 psi or more |
Because volume scales directly with thickness, moving a 400 square foot driveway from 4 inches to 6 inches raises the pour from about 4.9 to 7.4 cubic yards. That is a 50 percent jump, so the decision is worth making on purpose.
Always add a waste allowance
Never order your exact calculated volume. Subgrades are never perfectly level, forms bow, and some mix sticks in the chute. Industry practice is 5 to 10 percent extra for clean, formed pours on stable ground, and 10 to 15 percent for rough terrain or hand dug footings. The waste slider in the tool updates the order total as you change the percentage.
Estimating cost
Ready mix is priced by the cubic yard and set regionally, so the most accurate number comes from two local plants. Bagged concrete is priced per bag at home centers. The calculator lets you enter either a price per yard or a price per bag so the estimate matches how your supplier quotes. Ask the plant about the short load fee, which most charge on orders under a full truck, and about the minimum delivery, often one to one and a half yards. The National Ready Mixed Concrete Association publishes industry cost context if you want a benchmark.
Pick the calculator that fits your project
- Slab calculator for patios, driveways, garage floors and sidewalks
- Column calculator for round piers, sonotubes and square columns
- Footing calculator for strip footings, deck piers and foundations
- Bags calculator to turn any volume into a bag count
- How to calculate concrete guide for the full method, formulas and examples
Frequently asked questions
How much concrete do I need?
Multiply length by width by thickness in the same unit, then divide the cubic feet by 27 for cubic yards. A 10 by 10 slab at 4 inches needs about 1.23 cubic yards. Enter your sizes above and the tool adds waste and bag counts for you.
How many bags of concrete are in a cubic yard?
About 45 bags of 80 pound mix, 60 bags of 60 pound, or 90 bags of 40 pound, based on the yields on the bag. Check the yield printed on your product, since fast setting lines can differ.
How many cubic yards does a concrete truck hold?
A full load is usually about 10 cubic yards. Plants set a minimum delivery, often one to one and a half yards, and charge a short load fee below a full truck.
How much does a yard of concrete weigh?
Close to 4,050 pounds, or just over two tons, at the standard density of 150 pounds per cubic foot.
Is bagged concrete or ready mix cheaper?
Bags win under about one cubic yard. Above that, ready mix is usually cheaper per yard and saves hours of mixing. Around one to two yards it is close, so price both.
How accurate is this calculator?
It returns an exact geometric volume from the dimensions you enter. Real orders vary with subgrade, spillage and form movement, which is why you add a waste percentage before ordering.
References
- Quikrete, Concrete Mix 1101 product data sheet (bag yields and 28 day strength): https://www.quikrete.com/PDFs/DATA_SHEET-Concrete Mix 1101.pdf
- Portland Cement Association, Curing in Construction: https://cement.org/Learn/concrete-technology/concrete-construction/curing-in-construction
- ASTM C94, Standard Specification for Ready Mixed Concrete: https://www.astm.org/c0094_c0094m-22.html
- National Ready Mixed Concrete Association: https://www.nrmca.org
Methodology: volumes use length times width times thickness converted to a common unit, with 1 cubic yard equal to 27 cubic feet and bag counts from published manufacturer yields. Figures are estimates for planning. Confirm structural thickness, strength and reinforcement with a licensed engineer or your local building department. Recommended: publish this page under a named author with construction or engineering experience and add a review date.