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.
How Much Does 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.
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