Figure out how much concrete you need in about 30 seconds. Enter your project dimensions above, and the calculator returns volume in cubic yards, cubic feet, or cubic meters, plus the number of bags required.
Whether you're pouring a patio slab, setting fence posts, or forming footings, getting the right volume of concrete before you order saves money and keeps you from coming up short on pour day.
This is a free concrete calculator and estimator. Results are estimates based on standard mix ratios. Always confirm quantities with your supplier or contractor before purchasing.
Online Concrete Calculator and Estimator
Use this concrete calculator to calculate the amount of concrete for slabs, footings, columns, curbs, and more. Pick a shape, enter length, width, and thickness (or diameter and height), and the tool does the math instantly.
The calculator converts your dimensions into cubic yards of concrete for ready-mix orders and into bag counts for smaller projects. It supports US customary units and metric.
A few tips for accurate results:
- Measure twice. Small errors in thickness multiply fast across large areas.
- Round up, not down. Ordering 5 to 10 percent extra concrete accounts for spillage, uneven subgrade, and form irregularities.
- Use consistent units. Mixing feet and inches without converting is the most common mistake.
How to Calculate Concrete for Slabs
The basic formula for a rectangular slab is:
Length (ft) × Width (ft) × Thickness (ft) = Volume in cubic feet
Then divide by 27 to convert to cubic yards, because one cubic yard equals 27 cubic feet.
For example, a 10×10 slab that is 4 inches thick:
- Convert 4 inches to feet: 4 ÷ 12 = 0.333 ft
- 10 × 10 × 0.333 = 33.3 cubic feet
- 33.3 ÷ 27 = 1.23 cubic yards
You'd order about 1.25 to 1.35 cubic yards to have a small cushion.
How thick should a concrete slab be? Most residential slabs are 4 inches thick. Driveways that carry heavier vehicles often use 5 or 6 inches. A thicker slab uses more concrete but adds load capacity and durability.
How much concrete do I need for a 10×10 slab? At 4 inches thick, roughly 1.23 cubic yards. At 6 inches thick, roughly 1.85 cubic yards. The calculator above handles the math for any dimensions you enter.
Do I need rebar in my concrete slab? Rebar or welded wire mesh helps control cracking and adds tensile strength. For patios and walkways, mesh is common. Driveways and garage slabs benefit from rebar on a grid, typically #3 or #4 bars at 18 to 24 inch spacing. Local building codes may have specific requirements.
Concrete Slab for a Patio
A patio slab is perfect for slabs at the standard 4-inch thickness. Most residential patios range from 100 to 400 square feet.
To estimate concrete for a patio:
- Measure the length and width in feet.
- Use 4 inches (0.333 ft) as your thickness unless your plans call for more.
- Multiply length × width × thickness, then divide by 27.
How much does a concrete slab cost? Material cost varies by region and market. Ready-mix concrete typically runs $120 to $170 per cubic yard delivered, though prices fluctuate. Bagged concrete is cheaper per yard for tiny pours but more labor-intensive. The calculator estimates volume, not cost, so check local pricing after you know your yardage.
How much does concrete cost per square foot? Material only, a 4-inch slab costs roughly $2 to $4 per square foot for concrete. Installed cost (including labor, forms, finishing, and site prep) runs significantly higher.
Circular Slab
For a circular slab, the formula swaps in the radius:
π × Radius² × Thickness = Volume in cubic feet
- Measure the diameter and divide by 2 to get the radius.
- Multiply π (3.14159) × radius × radius × thickness (in feet).
- Divide by 27 for cubic yards.
Circular pads are common for fire pits, hot tub bases, and round planters. The calculator handles this shape automatically when you select the circular slab option.
Square Footings and Round Footings
Footings support walls, posts, and columns. They sit below the frost line and spread the load into the soil.
Square footings use the slab formula: length × width × depth. A typical deck post footing might be 16 × 16 inches and 12 inches deep.
Round footings (often formed with cardboard tubes like Sonotubes) use the circular formula: π × radius² × depth. Common tube diameters are 8, 10, and 12 inches.
Here's a quick reference for round footings 48 inches deep:
- 8-inch diameter tube: about 0.12 cubic feet per footing
- 10-inch diameter tube: about 0.18 cubic feet per footing
- 12-inch diameter tube: about 0.26 cubic feet per footing
Multiply by the number of footings, then convert to bags or yards.
How do I calculate concrete for a round column or pier? Use the same round footing formula. Measure the inner diameter of the form, convert to feet, and use the height of the pour as your depth.
Curb and Gutter Estimate
Curb and gutter sections have irregular cross-sections that make hand calculation tricky. The calculator simplifies this by asking for the curb height, gutter width, flag (top) width, and total length.
A standard residential curb-and-gutter profile is roughly 6 inches wide at the top, 18 inches deep on the curb face, and 12 to 24 inches of gutter width. Dimensions vary by local standards, so check your jurisdiction's spec drawings.
To estimate manually:
- Calculate the cross-sectional area of the curb and gutter profile in square inches.
- Convert that area to square feet (divide by 144).
- Multiply by the run length in feet to get cubic feet.
- Divide by 27 for cubic yards.
For long runs, even a small change in the cross-section adds up. Use the calculator to compare different profiles quickly.
Column Calculator
Concrete columns are either round or rectangular. Both shapes are straightforward.
Rectangular column: Length × Width × Height = cubic feet. Divide by 27 for cubic yards.
Round column: π × Radius² × Height = cubic feet. Divide by 27 for cubic yards.
Columns often need higher-strength mix designs (4,000 to 5,000 PSI) compared to a standard slab. They also typically require vertical rebar and ties. Check your structural plans for reinforcement and mix specifications before ordering.
Concrete Mix and Bag Estimator
Not every project justifies a ready-mix truck. For small pours, bagged concrete is practical.
Here's how many bags it takes to make one cubic yard:
| Bag Size | Bags per Cubic Yard |
|---|---|
| 40 lb | ~100 |
| 50 lb | ~80 |
| 60 lb | ~68 |
| 80 lb | ~45 |
How many 80 lb bags of concrete in a yard? About 45. Each 80 lb bag yields roughly 0.6 cubic feet, and one cubic yard is 27 cubic feet. So 27 ÷ 0.6 = 45 bags.
How many cubic feet is a 50-pound bag of concrete? About 0.37 cubic feet, though yield varies slightly by brand. Check the bag label.
Should I buy bagged concrete or have ready mix delivered? A good rule of thumb: if you need more than about 1 cubic yard, ready-mix delivery is usually cheaper and far less labor. Under half a yard, bags are often more convenient. Between 0.5 and 1 yard, it depends on your timeline, labor availability, and local delivery minimums.
What's the minimum amount of ready mix concrete I can order? Most ready-mix companies set a minimum order around 1 cubic yard, sometimes with a short-load fee for orders under 3 to 5 yards. Call your local plant for specifics.
How much does a yard of concrete weigh? Roughly 3,900 to 4,100 pounds, depending on the mix design and aggregate. That weight matters when planning truck access to your site.
Cement and Mortar Mix
Cement and concrete are not the same thing. Cement (Portland cement) is one ingredient in concrete. Concrete is the finished mix of cement, sand, gravel (aggregate), and water.
Mortar mix is cement, sand, and water, without the coarse aggregate. It's used for laying brick, block, and stone rather than pouring structural shapes.
What is the standard concrete mix ratio? A common general-purpose ratio is 1:2:3, meaning 1 part cement, 2 parts sand, 3 parts gravel by volume. Pre-bagged concrete products already include these proportions. For structural applications, a specific mix design (measured by PSI strength) replaces simple ratios.
What's the difference between concrete and cement? Cement is the powder binder. Concrete is the composite material made with cement, water, sand, and aggregate. Saying "cement patio" is technically inaccurate, but you'll hear it everywhere.
The calculator's bag estimator covers concrete products and mortar mix separately, since their yields per bag differ.
Concrete Estimates: What This Calculator Covers
This free concrete calculator handles seven common shapes and applications:
- Rectangular slabs (patios, driveways, garage floors, sidewalks)
- Circular slabs (fire pit pads, round patio sections)
- Square footings (deck posts, wall footings)
- Round footings (tube-formed piers, setting fence posts)
- Columns (rectangular and round)
- Curb and gutter sections
- Bag estimation for 40, 50, 60, and 80 lb bags of concrete
Results display in cubic yards, cubic feet, and cubic meters. The bag estimator converts volume into the number of bags you need for your project.
What this calculator does not do:
- It does not calculate concrete repair patch quantities for thin overlays.
- It does not provide structural engineering recommendations.
- It does not estimate rebar or reinforcement quantities.
- It does not account for waste beyond the extra percentage you add manually.
For complex shapes (stairs, curved walls, tapered footings), break the project into simpler geometric sections, calculate each one, and add the volumes together.
Pouring concrete stairs? Stairs are essentially stacked rectangular prisms. Calculate each step as a separate slab (tread depth × width × rise height), then sum them together with the landing. Add 10 to 15 percent for waste.
What PSI concrete should I use for a driveway? Most driveways use 3,500 to 4,000 PSI concrete. Standard sidewalks and patios often use 3,000 PSI. Check with your ready-mix supplier for their standard residential driveway mix.
Concrete Calculator FAQs
How do I calculate how much concrete I need? Measure length, width, and thickness in feet. Multiply all three. Divide by 27 to convert cubic feet to cubic yards. Or enter your dimensions into the calculator above and skip the math entirely.
How many square feet in a yard of concrete? It depends on thickness. At 4 inches thick, one cubic yard covers 81 square feet. At 6 inches thick, it covers 54 square feet. The formula is: 27 cubic feet ÷ thickness in feet = square feet of coverage.
How much is 1 yard of concrete? One cubic yard is 27 cubic feet of material. Delivered, ready-mix concrete costs roughly $120 to $170 per yard in most US markets, though prices vary by region and mix design.
How much does concrete weigh? Standard concrete weighs about 145 to 150 pounds per cubic foot, or roughly 3,900 to 4,100 pounds per cubic yard.
Can I mix concrete by hand vs ordering ready-mix? You can hand-mix small batches in a wheelbarrow or mixing tub. It's practical for half a cubic yard or less. Beyond that, the labor becomes extreme. A portable mixer helps for mid-size jobs. For anything over a yard, ready-mix delivery is faster and more consistent.
What is a RCC slab? RCC stands for roller-compacted concrete. It's a stiff, low-slump mix placed and compacted with rollers, commonly used for heavy-duty industrial floors and pavements. Residential projects rarely use RCC.
What's the difference between online tools and a physical construction calculator? Online calculators like this one are free and handle common shapes quickly. Physical construction calculators (handheld devices) can store custom formulas and work offline. For most homeowner and small contractor estimates, an online concrete calculator covers what you need.
How much does it cost to have a 20x20 concrete slab poured? Material cost alone for a 20×20 slab at 4 inches thick is about 2.5 cubic yards, or roughly $300 to $425 in concrete. Fully installed cost (labor, grading, forms, finishing) typically runs $2,400 to $4,800 depending on your area and site conditions. This calculator estimates volume, not total project cost.