Homeowner calculator
Concrete Calculator
Estimate concrete for slabs, continuous footings, and round post holes, including cubic yards, bags, and cost.
How this concrete calculator works
Concrete is estimated by volume. For slabs and footings, the calculator uses length × width × thickness. For post holes, it uses the volume of a cylinder.
Why bag yield matters
Concrete bags are sold by weight, but each bag has a volume yield. For accurate bag counts, use the cubic-foot yield printed on your bag.
Related project planning tools
Still deciding between concrete and pavers? Try the Paver Calculator to compare paver material needs.
Planning a wall near your concrete project? The Retaining Wall Calculator estimates blocks, caps, and drainage gravel.
Many concrete projects need a compacted base. Use the Gravel Calculator to estimate base gravel separately.
Setting posts for a fence? The Fence Cost Calculator estimates posts, panels, gates, concrete, and material cost.
Frequently asked questions
How do I calculate concrete for a slab?
Multiply slab length by width by thickness. This calculator converts thickness from inches to feet and estimates cubic feet, cubic yards, bags, and cost.
How many cubic feet are in a cubic yard of concrete?
There are 27 cubic feet in one cubic yard. Ready-mix concrete is commonly ordered by the cubic yard.
How many bags of concrete do I need?
Bag count depends on the total volume needed and the bag's cubic-foot yield. Enter the yield printed on your bag for the most accurate estimate.
What is the yield of an 80 lb bag of concrete?
Many 80 lb bags yield about 0.6 cubic feet, but you should check the specific bag label because yield can vary by product.
How thick should a concrete slab be?
Many light-duty residential slabs are around 4 inches thick, but the right thickness depends on load, use, soil, reinforcement, and local requirements.
How much concrete do I need for fence post holes?
Post hole concrete is based on the volume of a cylinder: hole diameter, hole depth, and number of holes. The post itself may displace some volume, so estimates can vary.
Should I order extra concrete?
Yes. A 5–10% overage helps account for uneven excavation, form variation, waste, and small measuring differences.
When should I use ready-mix instead of bags?
Ready-mix may be more practical for larger projects. Bagged concrete is often better for small slabs, repairs, footings, or post holes.
Does this calculator account for rebar or wire mesh?
No. This calculator estimates concrete volume only. Reinforcement needs depend on the project, load, local code, and professional guidance.
Can I use this for footings?
Yes, the concrete calculator includes a continuous footing option. Make sure footing dimensions meet project needs and local requirements.
How thick should a concrete slab be?
Many light-duty residential slabs are around 4 inches thick, but project load and local code matter.
Should I add overage?
Yes. 5–10% overage helps account for uneven excavation, form variation, and waste.