Concrete Calculator
Enter slab length, width, and depth to estimate how much concrete you need in cubic feet and cubic yards.
Also handy: Gravel Calculator, Raised-Bed Soil Calculator
Calculate concrete needed
Enter the slab length, width, and depth. This calculator estimates the total concrete volume required.
2.96 yd³
Based on a 20 ft by 12 ft slab at 4 inches deep.
How to use this calculator
Enter the slab length and width in feet, then enter the depth and choose inches or feet. The calculator estimates total area, cubic feet, and cubic yards of concrete required.
Tips for success
- Round up slightly. Always order a bit more than the bare estimate when buying ready-mix concrete.
- Patios and pads use inches. Most patios, walkways, and shed pads measure depth in inches, not feet.
- Account for uneven grade. Form irregularities and grade changes can increase the amount of concrete needed.
- Extra beats short. A small overorder is far cheaper than a second delivery or running out mid-pour.
- Plan for large pours. Projects over 2 yd³ often require scheduling delivery timing and extra finishing hands.
Common mistakes
- Confusing inches and feet for depth. Entering depth in inches but selecting feet (or vice versa) dramatically changes the result.
- Skipping the waste buffer. Not rounding up slightly for waste and uneven grade leads to shortfalls.
- Treating irregular forms as rectangles. Curved, L-shaped, or stepped pours need separate calculations per section.
- Forgetting footings and thick edges. Thickened slab edges and integral footings add significant extra volume.
- Ordering exact volume. Ordering the bare calculated amount leaves no safety margin.
FAQ
How many cubic feet are in one cubic yard?
One cubic yard equals 27 cubic feet.
Should I round up when ordering concrete?
Usually yes. Ordering a little extra helps prevent shortages during the pour.
Can I use this for patios and sidewalks?
Yes. This calculator is well suited for rectangular slabs such as patios, pads, and sidewalks.
What if my slab has thickened edges?
Calculate the main slab first, then separately calculate the extra edge volume and add it to the total.
Can I use feet instead of inches for depth?
Yes. This calculator supports either inches or feet for the depth input.