Slabs, square footings, or walls
Cubic feet--
Cubic yards--
Yards with waste--
Bags with waste--
Estimated bag cost--
Estimated ready-mix cost--
Practical note--
Concrete Calculator
Estimate concrete volume, bags, waste, and cost for slabs, footings, holes, and stairs.
Updated May 2026No signup requiredBuilt for mobile
How to use this calculator
- Enter the real numbers for your situation.
- Review the main result and any secondary results.
- Adjust inputs to compare practical scenarios.
- Use the estimate as a planning number before making a purchase or decision.
Formula
Volume or capacity is calculated from the measured inputs shown in the calculator.
Use the result summary to compare the calculated outputs
Add a reserve when real-world conditions can vary
This calculator uses practical estimating math. The exact formula depends on the inputs shown in the calculator card.
Worked examples
Basic example
Use the example numbers to understand the workflow, then enter measured values for a more realistic estimate.
Planning example
Increase the main quantity or add a buffer to see how the result changes before buying supplies or committing to a plan.
Practical planning tips
- Double-check units before trusting the result.
- Round up when running short would stop the job or trip.
- Use manufacturer labels, local rules, or professional guidance when safety matters.
- Save or print the result before going to the store or job site.
Safety and disclaimer note
This is a practical planning estimate. Verify safety, code, health, financial, or equipment decisions with the right professional or official source.
FAQ
Concrete Calculator questions
How accurate is the Concrete Calculator?
It is a planning estimate based on the numbers you enter. Real-world results can vary.
Should I add a buffer?
Yes when waste, weather, terrain, safety, or product variation could change the result.
Can I use the result for buying supplies?
Use it as a starting point, then confirm supplier packaging, labels, and local requirements.
Why do results vary?
Measurements, product specs, user habits, and field conditions can all change the final outcome.
Does this replace professional advice?
No. Use professional guidance for safety, health, code, legal, or financial decisions.
Concrete planning overview
This concrete calculator helps homeowners, DIYers, fence builders, landscapers, and small contractors estimate how much concrete a slab, footing, post hole, curb, tube, or stair form may need. It supports early decisions such as whether bagged concrete is realistic, whether ready-mix delivery is worth pricing, how much waste to include, and what budget range to expect before calling a supplier.
Use measured dimensions whenever possible. The result can guide material shopping, truck delivery questions, form planning, and whether the pour is small enough to mix by hand. It should not be the only source for structural work, frost footings, load-bearing slabs, or inspected projects.
Inputs explained
Length and width define the footprint. Thickness or height controls volume. Quantity repeats the same shape for multiple holes, pads, or steps. Waste covers spillage, uneven excavation, form movement, overdigging, and supplier rounding. Bag yield and price help compare store bags with ready-mix cubic yards.
Formula or method
Rectangular volume = length x width x thickness.
Cubic yards = cubic feet divided by 27.
Round hole volume = pi x radius squared x depth.
Order amount = calculated volume x (1 + waste percent).
Bag count = volume with waste divided by bag yield.
All dimensions must be in compatible units before multiplying. A four inch slab is one third of a foot, not four feet. For stairs, curbs, and tubes, the calculator estimates the practical shape from the dimensions shown in the tool rather than treating every job as a flat rectangle.
Worked example
A 10 ft by 12 ft patio at 4 inches thick is 10 x 12 x 0.333, or about 40 cubic feet. Divide by 27 and the slab is about 1.48 cubic yards before waste. With 10 percent extra, plan for about 1.63 cubic yards. If using 80 lb bags at about 0.60 cubic feet each, 40 cubic feet plus waste is about 44 cubic feet, or roughly 74 bags.
How to interpret the result
Round up when the pour cannot stop halfway, when holes are irregular, when the base is uneven, or when the supplier has delivery minimums. Confirm slab thickness, reinforcement, frost depth, footing size, drainage, and structural requirements with local code, a contractor, or an engineer when concrete supports a building, deck, retaining wall, vehicle load, or safety-critical structure.
Common mistakes
- Measuring slab thickness in inches but treating it like feet in the math.
- Ordering no extra for rough excavation, spillage, form gaps, or low spots.
- Comparing bag cost to ready-mix cost without considering labor, mixing time, and delivery minimums.
- Forgetting base preparation, compaction, reinforcement, joints, drainage, or curing conditions.
- Using a patio-style estimate for structural footings that should follow code or engineered plans.
Trust and disclaimer note
This is a planning estimate for material quantity and cost comparison. Confirm supplier yield, contractor guidance, site conditions, reinforcement, inspections, and local code where needed before ordering or pouring concrete.
FAQ
Concrete calculator planning questions
How much extra concrete should I order?
Small jobs often use 5 to 10 percent extra. Irregular holes, rough forms, hand-dug footings, and critical pours may need more because running short is usually worse than having a small amount left over.
When should I use ready-mix instead of bags?
Ready-mix becomes more attractive when the bag count is high, the pour must be placed quickly, or consistent mixing matters. Bags can still work for small pads, fence posts, and repairs.
Does this calculate reinforcement?
No. It estimates concrete volume and related buying quantities. Rebar, mesh, anchors, joints, and base preparation should be planned separately.
Can I use this for footings?
Use it for an early volume estimate, then verify footing depth, width, frost requirements, load requirements, and inspection rules with local code or a qualified professional.
Why do bag counts seem high?
Concrete bags yield a small amount of finished volume. Large slabs quickly require many bags, especially after waste is included.
How to use this concrete calculator
Start with the tab that matches the shape you are pouring: rectangular slabs, round holes, circular forms, curbs, or stairs. Enter measured dimensions, not nominal plan names, and keep units consistent. Use the waste field for overdigging, rough forms, spillage, low spots, and supplier rounding. Compare bag count with ready-mix yards before deciding how the concrete will be delivered or mixed.
Realistic concrete examples
Small shed pad
A 10 ft by 12 ft shed pad at 4 inches thick is about 40 cubic feet, or 1.48 cubic yards. With 10 percent waste, the order amount is about 1.63 cubic yards. If using 80 lb bags at about 0.60 cubic feet each, the same job is roughly 74 bags, which may make ready-mix worth pricing.
Fence post holes
Eight post holes that are 10 inches wide and 30 inches deep each use about 10.9 cubic feet before waste. With 15 percent extra for uneven digging and spillover, plan for about 12.5 cubic feet. At 0.60 cubic feet per 80 lb bag, that is about 21 bags.
Practical concrete tips
- Measure form depth after the base is compacted, not before excavation cleanup.
- Round up for hand-dug holes because sides are rarely perfectly straight.
- Price delivery fees, short-load fees, and mixing labor before choosing bags or ready-mix.
- Plan reinforcement, joints, anchors, drainage, and curing separately from volume.
- Do not use a simple volume estimate as approval for structural or inspected work.
What number should I use?
Use measured inputs first
Start with the actual number from your project, device, network, trip, or equipment label instead of a best guess.
Round in the safer direction
Round up for materials, food, water, storage, and capacity. Round down for runtime when running short would cause trouble.
Check related tools
Use the related calculators on this page to plan the next part of the job instead of treating one result as the whole answer.