Calculate Concrete Volume
Select a shape, enter dimensions, and get the exact amount of concrete you need -- in cubic yards, cubic feet, or cubic meters -- with bag estimates and cost.
How Concrete Volume Is Calculated
The volume depends on the shape of the pour. Here are the formulas used for each shape type:
Slab / Rectangle
The most common shape for patios, driveways, sidewalks, and floors. Make sure all measurements are in the same unit. For a typical 4-inch slab, convert inches to feet by dividing by 12 (4 in = 0.333 ft).
Cylinder / Column
Used for round columns, piers, sonotubes, and post footings. Enter the outer diameter and the height or depth of the pour. Multiply by the number of columns for the total.
Triangle
Used for triangular footings, ramps with tapered edges, or custom shapes. The "depth" is the thickness of the pour.
Curb / Gutter
A combined curb and gutter is calculated as two rectangular cross-sections extruded along the curb length. Leave gutter width and depth at zero if you only need the curb.
Unit Conversions
Bag Coverage Reference
Pre-mixed concrete bags yield approximately:
| Bag Size | Yield (ft³) | Yield (yd³) | Bags per yd³ |
|---|---|---|---|
| 40 lb | 0.30 | 0.011 | ~90 |
| 60 lb | 0.45 | 0.017 | ~60 |
| 80 lb | 0.60 | 0.022 | ~45 |
Actual yield may vary slightly by manufacturer. These are industry-standard estimates.
Common Slab Sizes Quick Reference
| Project | Typical Size | Depth | Approx. Volume |
|---|---|---|---|
| Sidewalk (20 ft) | 20' x 3' | 4" | 0.74 yd³ |
| Patio (10x10) | 10' x 10' | 4" | 1.23 yd³ |
| Single car pad | 10' x 20' | 4" | 2.47 yd³ |
| Double driveway | 20' x 20' | 5" | 6.17 yd³ |
| Garage floor | 24' x 24' | 4" | 7.11 yd³ |
| Post footing (12" dia) | 12" dia x 42" deep | -- | 0.12 yd³ each |
Concrete Ordering Tips
When to Use Ready-Mix vs. Bags
- Under 1 cubic yard: Bagged concrete is practical. About 45 bags of 80 lb mix.
- 1 to 2 cubic yards: Either option works. Ready-mix saves labor; bags avoid minimum delivery fees.
- Over 2 cubic yards: Ready-mix truck delivery is strongly recommended. Mixing 90+ bags by hand is grueling.
Always Order Extra
A 10% waste factor is standard practice. Concrete is wasted through:
- Spillage during pouring and screeding
- Uneven subgrade or forms that bow out slightly
- Over-excavation of the area
- Concrete left in the truck chute or mixer
Running short mid-pour creates a cold joint -- a structural weak point. It is always better to have a little extra than not enough.
Curing and Strength
- 24 hours: Initial set. Avoid walking on it.
- 48 hours: Can support light foot traffic.
- 7 days: Reaches ~70% of full strength. Remove forms.
- 28 days: Reaches ~99% of design strength (typically 3,000-4,000 PSI for residential).
Keep concrete moist for the first 7 days for best results. In hot weather, cover with plastic sheeting or use a curing compound.
Temperature Considerations
- Do not pour when temperatures are below 40 F (4 C) or above 90 F (32 C) unless you take special precautions.
- In cold weather, use warm water in the mix and insulating blankets.
- In hot weather, pour early morning, use cold water, and avoid direct sun on fresh concrete.
Frequently Asked Questions
How much concrete do I need for a 10x10 slab?
For a 10 ft x 10 ft slab at 4 inches thick, you need approximately 1.23 cubic yards of concrete (33.33 cubic feet). With a 10% waste factor, order about 1.36 cubic yards. That is about 56 bags of 80 lb pre-mix or one small ready-mix truck load.
How many 80 lb bags of concrete do I need per cubic yard?
One 80 lb bag yields approximately 0.60 cubic feet or 0.022 cubic yards. You need about 45 bags to make one cubic yard. For 60 lb bags, plan on about 60 bags per cubic yard. For 40 lb bags, about 90 bags per cubic yard.
How do I calculate concrete volume?
For a rectangular slab: multiply Length x Width x Depth (all in the same unit). Then convert to cubic yards by dividing cubic feet by 27. For cylinders, use pi x radius squared x height. Always add a waste factor of at least 10%.
Should I add extra concrete for waste?
Yes. A 10% waste factor is industry standard for most residential pours. For irregular shapes, sloped ground, or if you are less experienced with concrete work, consider adding 15% extra. Running short during a pour is far worse than having a small amount left over.
What is the difference between ready-mix and bagged concrete?
Ready-mix arrives pre-mixed in a truck and is pumped or poured directly into your forms. It is ideal for projects requiring more than 1-2 cubic yards. Bagged concrete (40, 60, or 80 lb bags) is dry mix you add water to on-site. It is better for small projects like post holes, small pads, and repairs.
How long does concrete take to cure?
Concrete reaches about 70% of its design strength in 7 days and near full strength at 28 days. You can walk on it after 24-48 hours in most conditions. Do not place heavy loads or drive on it for at least 7 days. Full curing takes 28 days.
What thickness should a concrete slab be?
Standard residential slabs are 4 inches thick. Driveways that support vehicles should be 5-6 inches. Garage floors are typically 4-6 inches. Footings and foundation walls follow local building codes, often 8-12 inches or more.
Does this calculator store my data?
No. All calculations run entirely in your browser. No data is sent to any server, and nothing is stored.
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Concrete Volume Calculator FAQ
How much concrete do I need for a 10x10 slab?
For a 10 ft x 10 ft slab at 4 inches thick, you need approximately 1.23 cubic yards of concrete. That is about 33.33 cubic feet. Plan to order 10% extra for waste, bringing the total to about 1.36 cubic yards.
How many 80 lb bags of concrete do I need per cubic yard?
One 80 lb bag of pre-mixed concrete yields approximately 0.6 cubic feet. Since one cubic yard equals 27 cubic feet, you need about 45 bags of 80 lb concrete per cubic yard.
How do I calculate concrete volume?
For a rectangular slab: Volume = Length x Width x Depth. For a cylinder or column: Volume = pi x radius squared x height. Convert all measurements to the same unit first, then convert the result to cubic yards by dividing cubic feet by 27.
Should I add extra concrete for waste?
Yes. A 10% waste factor is standard practice to account for spillage, uneven subgrade, over-excavation, and form irregularities. For complex shapes or uneven ground, consider 15% extra.
What is the difference between ready-mix and bagged concrete?
Ready-mix concrete is delivered by truck and is ideal for pours over 1-2 cubic yards. Bagged concrete (40, 60, or 80 lb bags) is mixed on-site and is best for small projects under 1 cubic yard. Ready-mix typically costs $125-$175 per cubic yard, while bagged concrete costs more per yard but requires no minimum order.
How long does concrete take to cure?
Concrete reaches about 70% of its full strength in 7 days and near full strength (99%) in 28 days. It can typically support foot traffic after 24-48 hours. Factors like temperature, humidity, and mix design affect curing time.
Does this calculator store my data?
No. All calculations run entirely in your browser. No data is sent to any server, and nothing is stored.