Concrete Volume Calculator
Use the concrete volume calculator below to get instant results.
Enter slab dimensions to calculate concrete needed.
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How to Calculate Concrete Volume
Calculating how much concrete you need comes down to one core formula: Length × Width × Thickness. The trick is getting your units right. Most people measure length and width in feet but thickness in inches, so you need to convert thickness to feet first by dividing by 12. Then, since concrete is sold by the cubic yard, you divide the total cubic feet by 27 (because 1 cubic yard = 27 cubic feet).
Here is the step-by-step formula:
- Measure your area in feet (length and width) and your thickness in inches.
- Convert thickness to feet: divide inches by 12. For example, 4 inches = 0.333 feet.
- Calculate cubic feet: Length × Width × Thickness (in feet). A 10 ft × 10 ft slab at 4 inches thick = 10 × 10 × 0.333 = 33.3 cubic feet.
- Convert to cubic yards: divide cubic feet by 27. So 33.3 ÷ 27 = 1.23 cubic yards.
- Add 10% for waste: you always lose some concrete to uneven subgrade, spillage, and over-excavation. 1.23 × 1.10 = 1.36 cubic yards to order.
For non-rectangular shapes like circular pads or footings, the formula changes. A round column footing uses π × radius² × depth. A 12-inch diameter sonotube that is 4 feet deep needs π × 0.5² × 4 = 3.14 cubic feet, or about 0.12 cubic yards. Our calculator above handles the standard rectangular slab, which covers the vast majority of residential concrete projects.
Concrete Mix Types: Ready-Mix vs. Bags
There are two main ways to get concrete for your project, and the right choice depends almost entirely on how much you need.
Bagged Concrete (Under 1 Cubic Yard)
Pre-mixed bags from brands like Quikrete and Sakrete come in 40 lb, 60 lb, and 80 lb sizes. You add water, mix in a wheelbarrow or mixer, and pour. An 80 lb bag yields about 0.6 cubic feet of concrete, which means you need 45 bags to make one cubic yard. At roughly $5 to $7 per 80 lb bag, one cubic yard of bagged concrete costs $225 to $315 in materials alone, plus significant labor mixing each bag.
Bagged concrete makes sense for small jobs: setting fence posts, pouring a mailbox pad, patching a step, or filling a few sonotube footings. Once you get past about 30 to 40 bags, the mixing time and physical effort become impractical.
Ready-Mix Delivery (1+ Cubic Yards)
Ready-mix concrete arrives on a truck already mixed to spec. A standard truck carries 8 to 10 cubic yards. Most suppliers have a minimum order of 1 yard, and many charge a short-load fee for orders under 3 to 5 yards. Ready-mix pricing typically runs $125 to $175 per cubic yard depending on your region and the mix design, with delivery fees of $50 to $100 on top.
For anything over 1 cubic yard, ready-mix is almost always cheaper and faster. A truck can pour a 20 × 20 driveway pad in under an hour. Doing the same project with bags would take an entire weekend and cost significantly more.
Short-Load and Trailer Options
If your project falls in the awkward 1 to 3 yard range, look into short-load trucks or concrete trailer rentals. Companies like Cart-Away rent small concrete mixers that you tow behind your truck, pre-loaded with the exact amount you need. This eliminates the short-load surcharge and gives you more working time than a ready-mix truck sitting in your driveway at $2 to $3 per minute of wait time.
Common Projects and Concrete Quantities
Here are ballpark concrete quantities for typical residential projects. All estimates assume standard 4-inch thickness unless noted, with 10% waste factor included.
| Project | Typical Size | Cubic Yards |
| Patio | 10 × 10 ft, 4 in | 1.36 |
| Patio (large) | 16 × 20 ft, 4 in | 4.35 |
| Single-car driveway | 10 × 20 ft, 5 in | 3.39 |
| Two-car driveway | 20 × 24 ft, 5 in | 8.15 |
| Sidewalk | 3 × 30 ft, 4 in | 1.22 |
| Shed pad | 10 × 12 ft, 4 in | 1.63 |
| Garage floor | 22 × 22 ft, 6 in | 9.88 |
| Foundation wall footing | 120 linear ft, 20 × 8 in | 4.94 |
| Fence post holes (20) | 10 in dia × 36 in deep each | 1.15 |
Driveways are typically poured at 5 to 6 inches thick rather than 4 inches, because they need to support vehicle weight. Most local codes require a minimum of 4 inches for residential driveways, but 5 inches is the practical standard, and 6 inches is recommended if heavy trucks will use the driveway.
Foundation footings vary widely by local building code and soil conditions. Residential footings are commonly 20 inches wide and 8 inches deep for single-story homes, and 24 inches wide and 12 inches deep for two-story structures. Always check your local code before ordering.
Shed and garage pads should use a compacted gravel base of at least 4 inches beneath the slab. For garages, reinforcing with wire mesh or rebar on 18-inch centers is standard practice. Fiber-reinforced concrete is a popular alternative for shed pads.
Our Calculation Methodology
The volume calculations in this tool follow ACI (American Concrete Institute) standards for residential and light commercial concrete work. All results include a standard 10% waste factor to account for over-excavation, uneven subgrade, spillage, and the concrete that stays in the chute and wheelbarrow. For most slab-on-grade projects, 10% is the industry-accepted margin; for complex shapes or sloped pours, you may want to increase that to 15%.
Material cost estimates are based on regional pricing surveys from major ready-mix suppliers and home improvement retailers across the United States. Actual costs vary by region, season, and order size. Bag yields (0.45 cu ft for 60 lb, 0.6 cu ft for 80 lb) are manufacturer-published figures from Quikrete and Sakrete. Ready-mix pricing reflects standard 4,000 PSI residential mix; specialty mixes (high-early, fiber-reinforced, colored) cost more.
Frequently Asked Questions
How much does a cubic yard of concrete weigh?
A cubic yard of standard concrete weighs approximately 4,050 pounds (about 2 tons). This matters for two reasons: your subgrade needs to support this weight, and if you are hauling bagged concrete in a pickup truck, remember that 45 bags of 80 lb mix (enough for one cubic yard) weighs 3,600 pounds, which exceeds the payload capacity of most half-ton trucks. Plan for multiple trips or have it delivered.
How long does concrete take to cure?
Concrete reaches about 70% of its full strength in 7 days and its rated strength (typically 4,000 PSI for residential work) at 28 days. You can walk on it after 24 to 48 hours, drive on a driveway after 7 days, and place heavy loads after 28 days. Curing continues slowly for months, but the 28-day mark is the engineering standard. Keep the surface moist for the first 7 days by misting with water or covering with plastic sheeting for the strongest result.
Can you pour concrete in the rain?
Light drizzle is generally fine if you cover the fresh pour with plastic sheeting. Heavy rain is a serious problem. Excess water mixing into the surface weakens the top layer, causes scaling and spalling, and can wash the cement paste away from the aggregate. If rain is forecast, either reschedule or have tarps and plastic ready to cover the pour immediately after finishing. Never try to work rainwater into the surface with a trowel.
What PSI concrete do I need?
For most residential work, 4,000 PSI is the standard mix. Sidewalks and patios can use 3,500 PSI. Driveways and garage floors should be at least 4,000 PSI. Foundation walls and footings typically require 3,500 to 4,000 PSI per code. For exposed aggregate or decorative work, use 4,000 to 4,500 PSI. Standard bagged concrete from the hardware store is usually 4,000 PSI. If you are ordering ready-mix, specify the PSI when you call.
Do I need rebar or wire mesh in my slab?
For a basic 4-inch patio or sidewalk on stable, well-compacted soil, wire mesh (6x6 W1.4/W1.4) is sufficient to control cracking. For driveways, most contractors use #3 or #4 rebar on 18-inch centers, or at minimum, wire mesh with fiber reinforcement. Garage slabs and any slab that will support significant loads should have rebar. Fiber-reinforced concrete (with synthetic or steel fibers mixed in) is increasingly popular as a mesh replacement for residential slabs, but it does not substitute for structural rebar where required by code.
How much does a concrete project cost?
Material costs for concrete itself run $125 to $175 per cubic yard for ready-mix, or $225 to $315 per cubic yard using 80 lb bags. But materials are only part of the total. A professionally installed 4-inch slab including excavation, gravel base, forms, concrete, finishing, and cleanup typically costs $6 to $12 per square foot. A 10 × 10 patio runs roughly $600 to $1,200 installed. A 20 × 24 two-car driveway at 5 inches thick runs $3,000 to $6,000 depending on your market and finish type.
How many bags of concrete do I need?
A standard 80 lb bag of premix concrete yields about 0.6 cubic feet when mixed. For 1 cubic yard (27 cubic feet), you would need approximately 45 bags. For projects over 1 cubic yard, ordering ready-mix delivery is usually more cost-effective, typically running $150 to $200 per yard delivered. To figure out your bag count, calculate total cubic feet (length × width × thickness in feet), add 10% for waste, and divide by 0.6 for 80 lb bags or 0.45 for 60 lb bags.
What is the difference between concrete and cement?
Cement is just one ingredient in concrete. It is the powder (Portland cement) that acts as a binder. Concrete is a mixture of cement, water, sand (fine aggregate), and gravel (coarse aggregate). When people say "cement mixer" or "cement truck," they usually mean concrete. The distinction matters when buying materials: a bag of "concrete mix" has everything you need, while a bag of "Portland cement" is just the binder and you would need to add your own sand and gravel.