Free planning tool for homeowners, DIY users, and contractors
Concrete Calculator
Estimate exact concrete volume, ready-mix order quantity, bag counts, waste allowance, concrete weight, and optional material cost for slabs, footings, walls, columns, post holes, stairs, curbs, and trenches.
Structural disclaimer
This calculator estimates material quantity only. Structural foundations, load-bearing slabs, engineered walls, and code-governed projects must follow local building codes and qualified design.
Project type
Choose the shape that matches your pour.
Rectangular Slab
Formula: Length x width x thickness x quantity
0.33 ft is about 4 in. Driveways are often 0.33-0.5 ft.
Dimension diagram
Waste, ordering, and cost
- 5%: simple rectangular forms
- 10%: typical residential projects
- 15%: complex pours
- 20%: irregular excavations
How the concrete calculations work
Rectangle
Length x width x height for slabs, footings, walls, columns, curbs, and trenches.
Cylinder
pi x radius squared x height for round columns, sonotubes, post holes, and circular slabs.
Stairs
Step volume is calculated as the sum of each solid step: width x run x rise x step index. Optional landing volume is added separately.
Waste
Waste is applied after exact geometry and before ready-mix rounding, bag counts, weight, and cost.
Typical residential thicknesses
- Patios and sidewalks: often about 4 inches.
- Driveways: often 4-6 inches depending on vehicle load and base.
- Garage and workshop floors: commonly 4 inches or more.
- Footings and foundations must follow local code and design requirements.
Ready-mix vs bags
- Use ready-mix for larger pours, slabs, driveways, patios, and jobs where placement speed matters.
- Use bags for small post holes, isolated repairs, patching, and very small pours.
- Bag mixing gets labor-heavy quickly. Compare cost, time, access, and finish quality.
- Always confirm minimum delivery quantities and short-load fees with suppliers.
Waste recommendations
- 5%: simple rectangular forms with careful measurements.
- 10%: typical residential slabs, walks, curbs, and posts.
- 15%: stairs, multiple forms, complex edges, or uneven subgrade.
- 20%: irregular excavations, rough post holes, or uncertain depth.
Common mistakes
- Entering inches as feet or forgetting to convert slab thickness.
- Ordering exact volume with no waste allowance.
- Ignoring uneven excavation, compacted base, low spots, or form leakage.
- Using this as structural design for load-bearing or code-governed work.
Need help pouring concrete?
Trusty Tri Handyman can help with patios, sidewalks, shed slabs, fence posts, concrete repairs, and small residential concrete projects across the Tri-Cities TN area.
Get a Free EstimateConcrete Calculator FAQ
How much waste should I add to a concrete order?
Use about 5% for simple rectangular forms, 10% for typical residential work, 15% for complex pours, and up to 20% for irregular excavations or rough post holes.
Should I order concrete by cubic yards or cubic meters?
In the United States, ready-mix concrete is usually ordered in cubic yards. Metric projects commonly use cubic meters. This calculator displays both.
How thick should a patio slab be?
Many residential patios are planned around 4 inches thick, depending on soil, base preparation, reinforcement, drainage, and local requirements.
How thick should a driveway slab be?
Many residential driveways use 4 to 6 inches of concrete, with heavier use requiring stronger design, reinforcement, base preparation, and local code review.
How thick should a sidewalk be?
Many sidewalks are about 4 inches thick for pedestrian use, but local code, soil, base material, and expected loads matter.
How deep should fence post holes be?
A common rule of thumb is to bury about one-third of the post length, but frost depth, soil, post height, wind load, and local codes can change the requirement.
Are bag yield values exact?
No. Bag yield varies by product and water content. The values here use common manufacturer-style yields for planning and always round bag counts up.
When should I use ready-mix instead of bags?
Ready-mix is usually better for larger slabs, driveways, patios, and pours where consistency and speed matter. Bags are practical for small post holes, patches, and isolated small projects.
Does this calculator include rebar or wire mesh?
No. It estimates concrete volume, bags, ready-mix quantity, waste, weight, and optional cost. Reinforcement design is a separate structural and code issue.
Can this calculator design a foundation?
No. Structural foundations, load-bearing slabs, retaining walls, and engineered projects must follow local building codes and qualified design requirements.
Why does the ready-mix order round up?
Concrete trucks and suppliers often use order increments. Rounding up helps avoid running short during placement.
What concrete density does the weight estimate use?
The calculator uses standard normal-weight cured concrete density: about 150 lb per cubic foot or 2400 kg per cubic meter.
Do stairs use a simple rectangle formula?
No. The stair calculator sums each solid step volume using width x run x rise x step index, then adds the optional landing volume. This matches a solid stepped concrete form better than a single rectangle.
What is the most common mistake when estimating concrete?
Common mistakes include mixing inches and feet, forgetting thickness conversion, skipping waste, ignoring uneven excavation, and not checking local code requirements.
Can Trusty Tri Handyman help with small concrete projects?
Yes. Trusty Tri Handyman can help with patios, sidewalks, shed slabs, fence posts, concrete repairs, and small residential concrete projects in the Tri-Cities TN area.