Concrete Calculator
Pouring a patio? Setting a fence post? Don't make multiple trips to the hardware store. Calculate exactly how many bags or yards you need in seconds.
Slab Dimensions
The Heavy Maths of Hardscaping
Concrete is heavy, messy, and time-sensitive. Once you start mixing water, the clock is ticking. The worst feeling in construction is running out of concrete when your slab is 90% poured.
Our Concrete Calculator solves this logistics nightmare. Whether you are buying 80lb bags of Quikrete from Home Depot or ordering a truck from a batch plant, we give you the precise volume needed to finish the job.
Understanding the Units
To order correctly, you need to speak the language of the trade.
Cubic Yards (yd³)
This is volume. Length x Width x Depth. Ready-mix trucks are ordered by the yard. A small truck holds 3-4 yards; a large one holds 9-10 yards.
Pre-Mix Bags
Sold as 60lb (0.45 cubic feet) or 80lb (0.60 cubic feet). Great for small jobs like setting a mailbox or small landing strip.
Slabs (Square)
Most common. Used for driveways, patios, and sidewalks. Key measurement is consistent thickness (usually 4 inches).
Footings (Circular)
Used for deck posts or fence poles. Calculation involves the radius of the hole (pi * r² * depth).
Fence Posts
A standard 4x4 fence post in a 10-inch diameter hole, 2 feet deep, takes roughly 1.5 to 2 bags of 60lb concrete.
Patio Slabs
A 10x10 patio at 4 inches thick requires about 1.25 cubic yards. That's over 50 bags—definitely time to consider a delivery truck!
Driveway Assessment
Check if a contractor's quote for "6 yards" is accurate for your driveway size. Knowledge saves you money regardless of who pours it.
Frequently Asked Questions
Should I add a safety margin?
Yes! The industry standard is 5-10% extra. This accounts for spillage, uneven subgrade (ground isn't perfectly flat), and form bowing. Running short is a disaster; having left over is just a doorstop.
Do I wet the dirt first?
Yes. Dry soil sucks moisture out of the wet concrete, weakening it. This doesn't change the volume calculation, but it is a critical tip for a successful pour.
Can I return unused bags?
Usually yes, as long as they haven't gotten wet or hardened. However, moving 80lb bags back into your truck is back-breaking work, so accurate calculation prevents injury too!
Structural Advice
This calculator provides volume estimates only. It cannot tell you if your soil can support the weight or if you need rebar. Consult a structural engineer for large projects.
Privacy
We do not store your calculations. Your project details stay in your browser.