Concrete estimating, without the guesswork
Free Concrete Calculator
Use this free concrete calculator to choose your pour shape, enter its measurements, and get cubic yards with waste, bag counts and a ballpark ready mix cost. Works for slabs, footings, columns, circular tubes and solid concrete stairs.
Reviewed September 10, 2026 by Sam Johnson from the Concrete Calculators Editorial Team. Published formulas and editable planning assumptions are identified below.
Concrete to order
cubic yards, rounded for ordering
- Calculated volume
- 5.43 cu yd
- Before waste
- 4.94 cu yd
- Cubic feet
- 146.7
- 80 lb bags instead
- 245
- 60 lb bags instead
- 326
- 40 lb bags instead
- 489
- Weight when cured
- 10.00 tons
- Ready mix cost, about
- $908
Most ready mix plants charge a short load fee for orders under 8 to 10 cubic yards. Ask the dispatcher what the fee is before you order.
Take this estimate with you
How the concrete calculator works it out
The concrete calculator multiplies length by width to get the area, then multiplies by the thickness converted to feet. That gives cubic feet. Divide by 27, because a cubic yard is 27 cubic feet. The waste allowance goes on last. Footings work the same way with the trench width and depth. Columns use the circle area, diameter squared times 0.785, times the height.
A worked concrete calculator example
Worked example: a 20 by 20 ft patio at 4 inches. The area is 400 sq ft. Four inches is 0.333 ft, so the volume is 133.3 cubic feet. Divided by 27 that is 4.94 cubic yards. With 10 percent waste you need 5.43, and the plant will batch it as 5.5 on the ticket.
When to switch to a cost calculator
This concrete calculator stops at volume on purpose. To price the same pour with base rock, reinforcement and labor, use the concrete slab cost calculator. For a simple shed or equipment base, the concrete pad cost calculator is faster.
Concrete bag yields by size
Yields below are the manufacturer figures printed on the bag, and the concrete calculator above applies them to every bag size at once. Divide your cubic feet by the yield to get bags, and always round up.
| Bag size | Yield per bag | Bags per cubic yard |
|---|---|---|
| 80 lb | 0.60 cu ft | 45 |
| 60 lb | 0.45 cu ft | 60 |
| 50 lb | 0.375 cu ft | 72 |
| 40 lb | 0.30 cu ft | 90 |
| 25 kg | 0.0125 m³ | 80 per m³ |
| 20 kg | 0.010 m³ | 100 per m³ |
Bags or a ready mix truck
Bags make sense under about one yard. Past that, mixing 45 or more bags by hand costs you a day and the material savings disappear. Current delivered truck prices are in the concrete price per yard guide.
Pick the right concrete calculator for the job
Every concrete calculator on this site asks different questions on purpose, so you are never pricing a floor with a patio's inputs.
| Calculator | Built for | What it adds |
|---|---|---|
| Concrete pad cost calculator | Shed, hot tub and equipment pads | Use presets that set size, thickness and reinforcement |
| Concrete slab cost calculator | Patios, driveways, garage slabs | Finish types, thickened edges, vapor barrier, control joint counts |
| Concrete floor cost calculator | Interior floors | Polish, stain and seal pricing, topping mode, pump day |
| Concrete block calculator | Block walls | Blocks, mortar bags, sand and pallets with openings subtracted |
What changes how much concrete you order
- Subgrade cut too deep. An extra half inch of depth on a 400 sq ft slab is another 0.6 yards. This is the number one reason pours come up short.
- Forms bowing outward on long runs, which quietly thickens the edges.
- Slope across the pour. Measure thickness at the thin end and the thick end and use the average.
- Thickened edges or interior footings that were not in the simple length by width math.
- Pump line waste. A trailer pump holds concrete you pay for but never place.
What this number does not cover
Forms, stakes, reinforcement, base rock and cure compound are not part of this number. They are priced in the cost calculators above.
Concrete guides
- Broom finish concrete
The default flatwork finish: why it wins on traction, the timing window that decides it, and what it costs.
- Concrete control joints
Plan the panel layout, groove depth and cutting window before the concrete truck arrives.
- How thick should a concrete driveway be
4 inches is the minimum, 5 is the smart pour. Thickness by vehicle, climate and cost.
- Concrete mix ratio
What 1:2:3 actually means, which ratio suits which job, and the number that matters more than any of them.
- Concrete pad for a shed
Sizing, thickness, base and cost for the pad under a backyard shed, with the numbers you can order against.
- Concrete price per yard
What a yard costs delivered, by psi, and the fees the dispatcher does not volunteer.
- Concrete PSI and mix strength
Read a strength rating, compare mix options and separate concrete PSI from slab load capacity.
- Concrete vs asphalt driveway
The two materials compared on the four things that actually decide it: cost, lifespan, climate and what each asks of you later.
- Concrete vs cement
Cement is the powder, concrete is the material. Which bag to buy and why it matters.
- Exposed aggregate concrete
The washed stone finish explained: how it is produced, what it adds per square foot and what it asks for in return.
- How long does concrete take to dry
Walk on it at 24 hours, drive on it at 7 days, full strength at 28. What moves those numbers.
- How much does a yard of concrete weigh
About 4,050 lb, or 2 tons, per cubic yard. What that means for trailers, forms and floors.
- Vapor barrier under concrete slab
When it is required, what mil to use, and why the sand layer argument was settled.
Straight answers
Concrete calculator questions
Open a question for the practical answer, including the assumptions behind the number.
How much concrete do I need for a 20 by 20 slab?
At 4 inches thick, a 20 by 20 ft slab takes 4.94 cubic yards before waste. With the 10 percent allowance the concrete calculator applies by default you need 5.43, so you would order 5.5 yards.
How many bags of concrete make a cubic yard?
Using the yields printed on the bags: 45 bags at 80 lb, 60 bags at 60 lb, 72 bags at 50 lb, or 90 bags at 40 lb. That is why bags stop making sense much past one yard.
What waste percentage should I use?
10 percent is the safe default for slabs on grade. Drop to 5 only when the base is compacted flat and the forms are tight. Rough trenches and hand dug footings can eat 15 or more.
Should I order ready mix or mix bags?
The break-even sits around one cubic yard. Below it, bags mixed on site are cheaper once you count the short load fee on a small truck order. Above it, the truck wins on both price and quality. The concrete calculator shows bags and truck cost side by side so you can compare.
How much does a yard of concrete cost delivered?
Our default is $165 per cubic yard, a national average for 3,500 psi mix that we review quarterly. Real quotes typically land between $130 and $220 depending on region, mix strength and fuel surcharges.
Concrete tool library
All free concrete calculators
Pick the scope that matches your pour. Every available calculator is free to use.
Free Concrete Pad Cost Calculator
Materials and labor price for a simple outdoor pad.
Open calculator →
Free Concrete Slab Cost Calculator
Slab pricing with finish, thickened edges and vapor barrier.
Open calculator →
Free Concrete Floor Cost Calculator
Interior floor pricing with polish, stain and topping modes.
Open calculator →Free Concrete Slab Calculator
Yards, bags and rebar for any slab.
In developmentFree Concrete Yardage Calculator
Straight to cubic yards for any shape.
In developmentFree Concrete Bag Calculator
Bag counts by brand and bag size.
In developmentFree Concrete Footing Calculator
Strip and pad footings by the trench.
In developmentFree Concrete Column Calculator
Round columns, tubes and post holes.
In developmentConcrete guides to read next
- Concrete mix ratio
What 1:2:3 actually means, which ratio suits which job, and the number that matters more than any of them.
- Concrete price per yard
What a yard costs delivered, by psi, and the fees the dispatcher does not volunteer.
- Concrete vs asphalt driveway
The two materials compared on the four things that actually decide it: cost, lifespan, climate and what each asks of you later.
What changed on this page
- Read next now includes the concrete mix ratio guide, which pairs with the bag counts this tool returns.
- Read next now includes the concrete vs asphalt driveway comparison.
- Per field unit choice added: feet, inches, yards, meters and centimeters.
- Copy, email and print estimate actions added, plus saved inputs between visits.
- Tube and stair shapes added alongside slab, footing and column.
Prices and formulas are reviewed on the schedule described in our methodology.