How Do I Calculate How Much Concrete I Need?
Multiply length × width × depth (in feet) and divide by 27 to get cubic yards. A 10×10 slab at 4 inches thick needs 1.23 cubic yards, or about 56 bags of 80-pound concrete mix. Add 5–10% for waste. Enter your dimensions above for an instant estimate with bag counts.
Concrete is sold by the cubic yard. One cubic yard equals 27 cubic feet. To calculate how much concrete you need, multiply your project's length × width × depth (all in feet), then divide by 27.
For slabs and footings: Measure length and width in feet. Measure depth in inches (standard slab is 4 inches). The calculator converts inches to feet automatically.
For round columns: Enter the diameter in inches and height in inches. The calculator uses πr²h to compute the volume of each column, then multiplies by the number of columns.
Why Add a Waste Factor?
Always order 5-10% more concrete than your exact calculation. Waste comes from uneven subgrade, spillage, and over-excavation. For complex pours (curves, steps, or forms with many angles), increase the waste factor to 10-15%.
When Should I Use Ready-Mix vs. Bagged Concrete?
Use ready-mix delivery for any project over 1 cubic yard. An 80-pound bag yields only 0.6 cubic feet — you need 45 bags per cubic yard, totaling over 3,600 pounds of material to mix by hand. Ready-mix is faster, cheaper per yard, and produces a more consistent pour.
For projects over 1 cubic yard, ready-mix delivery is more economical and practical. An 80-pound bag of concrete mix yields approximately 0.6 cubic feet. That means you need 45 bags per cubic yard — over 3,600 pounds of material to mix by hand.
How Thick Should a Concrete Slab Be?
Most residential slabs are 4 inches thick. Sidewalks and patios use 4 inches. Driveways and garage floors need 4–6 inches depending on vehicle weight. Footings run 8–12 inches, and foundation walls 8–10 inches. Thicker pours require rebar reinforcement.
- Sidewalks: 4 inches
- Driveways: 4-6 inches
- Garage floors: 4-6 inches
- Footings: 8-12 inches
- Foundation walls: 8-10 inches
How Many Bags of Concrete for a 10x10 Slab
A 10×10-foot slab at 4 inches thick requires 1.23 cubic yards — about 56 bags of 80-lb mix or 74 bags of 60-lb mix. At 6 inches thick, the same slab needs 1.85 cubic yards (84 bags of 80-lb). Add 10% for waste on uneven subgrades.
A 10×10 slab is one of the most common DIY concrete projects — patios, sheds, and small pads. The volume and bag count depends on the thickness you pour. Here's a quick reference table based on the standard 80 lb bag (0.6 cu ft yield) and 60 lb bag (0.45 cu ft yield):
| Thickness | Cubic Yards | 80 lb Bags | 60 lb Bags |
|---|---|---|---|
| 4" | 1.23 | ~56 | ~74 |
| 5" | 1.54 | ~70 | ~93 |
| 6" | 1.85 | ~84 | ~112 |
These figures already assume a clean pour. Add a 10% waste factor if your subgrade is uneven or you're pouring around forms with tight corners.
Cost varies by region. The Estimated Material Cost card pulls from our indicative national-average pricing dataset(refreshed quarterly). Northeast and California metros run 15–40% above the national midpoint while Midwest and Southeast metros run 5–15% below — verify locally for binding quotes.
How Much Does Ready-Mix Concrete Cost?
Ready-mix concrete typically runs $125–$150 per cubic yard delivered in most US markets, though prices vary by region, distance from the plant, and minimum-load fees. Bagged concrete costs $6–$8 per 80 lb bagat retail, which works out to roughly $270–$360 per cubic yard if you mix by hand. Ready-mix is almost always cheaper past 1 cubic yard once you factor in the labor of mixing bags.
Short-load fees kick in below 3–4 cubic yards with most suppliers. If your project is between 1 and 3 yards, call two or three local plants and ask about their minimums — the spread can be significant.
Do I Need Rebar?
Use wire mesh or fiber for 4-inch patios and walkways; use #4 rebar at 18–24-inch spacing for driveways, garage slabs, and any load-bearing slab. Footings always require rebar — typically two #4 bars running the full length, tied to vertical bars for walls or columns.
Reinforcement keeps concrete from cracking apart once it develops hairline cracks (which it will). The right reinforcement depends on the load:
- 4" patios, walkways, shed pads: wire mesh or fiber reinforcement is usually sufficient. Rebar is optional.
- Driveways, garage floors, structural slabs:use #4 rebar on 18–24 inch centers in both directions, supported on chairs so the rebar sits in the middle third of the slab.
- Footings:always rebar — typically two #4 bars running the length of the footing, tied to vertical bars for walls or columns.
Common Concrete Slab Sizes
Pre-calculated bag counts for popular DIY slab dimensions. Each row uses the standard 80 lb (0.6 cu ft) and 60 lb (0.45 cu ft) bag yields. Add a 10% waste factor for uneven subgrade or formed corners.
How Many Bags of Concrete for a 10×12 Slab?
A 10×12-foot slab at 4 inches thick needs 1.48 cubic yards — about 67 bags of 80-lb mix or 89 bags of 60-lb mix. At 6 inches the same slab needs 2.22 cubic yards (100 bags of 80-lb). 10×12 is a common shed-pad and small-patio size.
| Thickness | Cubic Yards | 80 lb Bags | 60 lb Bags |
|---|---|---|---|
| 4" | 1.48 | ~67 | ~89 |
| 6" | 2.22 | ~100 | ~134 |
How Many Bags of Concrete for a 12×12 Slab?
A 12×12-foot slab at 4 inches thick needs 1.78 cubic yards — about 80 bags of 80-lb mix or 107 bags of 60-lb mix. At 6 inches it climbs to 2.67 cubic yards (120 bags of 80-lb). 12×12 is the most common DIY backyard patio size.
| Thickness | Cubic Yards | 80 lb Bags | 60 lb Bags |
|---|---|---|---|
| 4" | 1.78 | ~80 | ~107 |
| 6" | 2.67 | ~120 | ~160 |
How Many Bags of Concrete for a 12×16 Slab?
A 12×16-foot slab at 4 inches thick needs 2.37 cubic yards — about 107 bags of 80-lb mix or 143 bags of 60-lb mix. At 6 inches the slab needs 3.56 cubic yards (160 bags of 80-lb). 12×16 fits a large shed, workshop, or pool-house pad.
| Thickness | Cubic Yards | 80 lb Bags | 60 lb Bags |
|---|---|---|---|
| 4" | 2.37 | ~107 | ~143 |
| 6" | 3.56 | ~160 | ~214 |
How Many Bags of Concrete for a 16×16 Slab?
A 16×16-foot slab at 4 inches thick needs 3.16 cubic yards — about 143 bags of 80-lb mix or 190 bags of 60-lb mix. At 6 inches the same slab needs 4.74 cubic yards (214 bags of 80-lb). At this size, ready-mix delivery is faster and cheaper than mixing bags by hand.
| Thickness | Cubic Yards | 80 lb Bags | 60 lb Bags |
|---|---|---|---|
| 4" | 3.16 | ~143 | ~190 |
| 6" | 4.74 | ~214 | ~285 |
How Many Bags of Concrete for a 20×20 Slab?
A 20×20-foot slab at 4 inches thick needs 4.94 cubic yards — about 223 bags of 80-lb mix or 297 bags of 60-lb mix. At 6 inches it needs 7.41 cubic yards (334 bags of 80-lb). 20×20 covers a generous single-car garage or large patio. Use ready-mix at this volume.
| Thickness | Cubic Yards | 80 lb Bags | 60 lb Bags |
|---|---|---|---|
| 4" | 4.94 | ~223 | ~297 |
| 6" | 7.41 | ~334 | ~445 |
How Many Bags of Concrete for a 20×24 Slab?
A 20×24-foot slab at 4 inches thick needs 5.93 cubic yards — about 267 bags of 80-lb mix or 356 bags of 60-lb mix. At 6 inches it needs 8.89 cubic yards (400 bags of 80-lb). 20×24 covers a compact 2-car garage or oversized workshop pad. Order ready-mix at this volume.
| Thickness | Cubic Yards | 80 lb Bags | 60 lb Bags |
|---|---|---|---|
| 4" | 5.93 | ~267 | ~356 |
| 6" | 8.89 | ~400 | ~534 |
How Many Bags of Concrete for a 24×24 Slab?
A 24×24-foot slab at 4 inches thick needs 7.11 cubic yards — about 320 bags of 80-lb mix or 427 bags of 60-lb mix. At 6 inches the slab needs 10.67 cubic yards (480 bags of 80-lb). 24×24 is the standard 2-car garage footprint — always order ready-mix at this volume.
| Thickness | Cubic Yards | 80 lb Bags | 60 lb Bags |
|---|---|---|---|
| 4" | 7.11 | ~320 | ~427 |
| 6" | 10.67 | ~480 | ~640 |
How Many Bags of Concrete for a 30×30 Slab?
A 30×30-foot slab at 4 inches thick needs 11.11 cubic yards — about 500 bags of 80-lb mix or 667 bags of 60-lb mix. At 6 inches it needs 16.67 cubic yards (750 bags of 80-lb). 30×30 covers a 3-car garage or detached shop. Bagged mix is impractical at this volume.
| Thickness | Cubic Yards | 80 lb Bags | 60 lb Bags |
|---|---|---|---|
| 4" | 11.11 | ~500 | ~667 |
| 6" | 16.67 | ~750 | ~1,000 |
Concrete for Footings, Piers, and Post Holes
Pre-calculated bag counts for the most common footing, sonotube pier, and fence post hole sizes. Cylinder volumes use π × r² × h. Add a 10% waste factor for over-excavation and spillage when augering.
How Much Concrete for a 12-Inch Wide × 8-Foot Footing?
A 12-inch wide by 8-foot long strip footing at 8 inches deep needs 0.20 cubic yards — about 9 bags of 80-lb mix or 12 bags of 60-lb mix. At 12 inches deep the same footing needs 0.30 cubic yards (14 bags of 80-lb). Always reinforce with two #4 rebar runs.
| Depth | Cubic Yards | 80 lb Bags | 60 lb Bags |
|---|---|---|---|
| 8" | 0.20 | ~9 | ~12 |
| 12" | 0.30 | ~14 | ~18 |
How Much Concrete for a 10-Inch Sonotube (4 ft Tall)?
One 10-inch diameter sonotube at 4 feet tall needs 0.08 cubic yards — about 4 bags of 80-lb mix or 5 bags of 60-lb mix per tube. A four-pier deck set needs 0.32 cubic yards (15 bags of 80-lb). 10-inch tubes suit deck piers and small structural posts.
| Quantity | Cubic Yards | 80 lb Bags | 60 lb Bags |
|---|---|---|---|
| 1 tube | 0.08 | ~4 | ~5 |
| 4 tubes | 0.32 | ~15 | ~20 |
How Much Concrete for a 12-Inch Sonotube (4 ft Tall)?
One 12-inch diameter sonotube at 4 feet tall needs 0.12 cubic yards — about 6 bags of 80-lb mix or 7 bags of 60-lb mix per tube. A four-pier deck set needs 0.47 cubic yards (21 bags of 80-lb). 12-inch tubes are the most common deck and porch pier size.
| Quantity | Cubic Yards | 80 lb Bags | 60 lb Bags |
|---|---|---|---|
| 1 tube | 0.12 | ~6 | ~7 |
| 4 tubes | 0.47 | ~21 | ~28 |
How Much Concrete for a 16-Inch Sonotube (4 ft Tall)?
One 16-inch diameter sonotube at 4 feet tall needs 0.21 cubic yards — about 10 bags of 80-lb mix or 13 bags of 60-lb mix per tube. A four-pier set needs 0.83 cubic yards (38 bags of 80-lb). 16-inch tubes are sized for heavy loads — second-story decks, carports, and pole barns.
| Quantity | Cubic Yards | 80 lb Bags | 60 lb Bags |
|---|---|---|---|
| 1 tube | 0.21 | ~10 | ~13 |
| 4 tubes | 0.83 | ~38 | ~50 |
How Much Concrete for a 10-Inch Fence Post Hole (3 ft Deep)?
One 10-inch diameter fence post hole at 3 feet deep needs 0.06 cubic yards — about 3 bags of 80-lb mix or 4 bags of 60-lb mix per hole. A 10-post fence run needs 0.61 cubic yards (28 bags of 80-lb). 10-inch holes suit 4×4 posts in non-frost-line soils.
| Quantity | Cubic Yards | 80 lb Bags | 60 lb Bags |
|---|---|---|---|
| 1 hole | 0.06 | ~3 | ~4 |
| 10 holes | 0.61 | ~28 | ~37 |
How Much Concrete for a 12-Inch Fence Post Hole (3 ft Deep)?
One 12-inch diameter fence post hole at 3 feet deep needs 0.09 cubic yards — about 4 bags of 80-lb mix or 6 bags of 60-lb mix per hole. A 10-post fence run needs 0.87 cubic yards (40 bags of 80-lb). 12-inch holes suit 6×6 posts, gate posts, and corner braces under load.
| Quantity | Cubic Yards | 80 lb Bags | 60 lb Bags |
|---|---|---|---|
| 1 hole | 0.09 | ~4 | ~6 |
| 10 holes | 0.87 | ~40 | ~53 |
Related Guides
- How to Pour a Concrete Slab — Eight-step pour guide covering planning, forms, sub-base, reinforcement, screed, float, control joints, and cure
How Much Does Ready-mix concrete Cost?
Ready-mix concrete averages about $165.00 per cubic yard nationally as of our April 2026 research. Standard 3000-3500 PSI mix, full truckload (10+ yards), delivery within ~20 mi. Regional variation is significant — Northeast and California metros run 15–40% above the national midpoint while Midwest and Southeast metros run 5–15% below. See our pricing methodology for sources and confidence tiers.
Find Concrete Prices in Your State
Construction material pricing varies meaningfully by state. See per-metro concrete pricing for the 5 states we currently cover:
- Concrete prices in California
- Concrete prices in Texas
- Concrete prices in Florida
- Concrete prices in New York
- Concrete prices in New Jersey
Related Calculators
- Rebar Calculator — Calculate rebar spacing and weight
- Gravel Calculator — Estimate gravel for your sub-base
- Sand Calculator — Calculate sand for bedding
Written by Daniel McCarney — AceCalc