How concrete volume is measured
Concrete volume measures the space inside the forms or excavation. Length, width, and depth must use consistent units before multiplying.
Concrete Calculator
Calculate how much concrete you need for slabs, columns, and footings.
Project dimensions
Choose a project shape, enter dimensions, and add a waste buffer for planning.
Concrete needed
1.36
cubic yards, including waste buffer
Cubic feet
36.67 ft³
Cubic meters
1.04 m³
Waste-adjusted volume
1.36 yd³
Ready-mix order amount
1.36 yd³
Estimated bag count
62 bags
Estimated cost
Add price
Project area
100.00 ft²
Quantity used
1 project
Copy result
Copy the concrete volume, bag count, waste buffer, cost estimate, and project summary.
Waste buffer note
A buffer helps account for uneven base, form variation, and small measurement differences.
Bag yield note
Bag yield varies by product. Check the label before buying bags.
Ready-mix estimate
Suppliers may round orders and apply delivery minimums or fees.
Measurement accuracy
Depth and thickness have a large effect on concrete volume.
Local calculation
Inputs are processed in your browser. No external pricing API is required.
Dynamic construction insights
Material choice
This estimate is suitable for planning, but final needs may vary with forms, base preparation, and site conditions.
Waste buffer
The selected waste buffer adds a planning margin to the base concrete volume.
Project planning
Check product labels, supplier guidance, and local requirements before ordering.
Concrete project breakdown
Base volume
33.33 ft³
Waste buffer amount
3.33 ft³
Final recommended volume
1.36 yd³
Bag or ready-mix amount
62 bags or 1.36 yd³
Estimated cost
Add price to estimate
Project dimensions
10 feet x 10 feet x 4 inches
Common slab thickness guide
Walkway
3 to 4 in
Typical light foot traffic range
Patio
4 in
Common for many residential patios
Shed base
4 to 6 in
Depends on shed size, soil, and load
Driveway
4 to 6 in
Vehicle loads may require more planning
Garage slab
4 to 6 in
Check local requirements and project plans
Concrete bag yield guide
40 lb bag
About 0.30 ft³
Useful for small patching work
50 lb bag
About 0.375 ft³
Yield varies by mix and product
60 lb bag
About 0.45 ft³
Common DIY bag size
80 lb bag
About 0.60 ft³
Common for larger small projects
Cubic yard reference
1 cubic yard
27 cubic feet
Common ready-mix ordering unit
10 ft x 10 ft x 4 in
About 1.23 yd³
Before adding waste buffer
12 in x 36 in post hole
About 0.09 yd³
Before subtracting post volume
Waste buffer guide
Simple formed slab
5% to 10%
Works when forms and base are consistent
Uneven base
10% to 15%
Depth variation can increase volume
Footings
10%+
Excavation shape can vary by site
Post holes
10% to 20%
Hole diameter and depth can change quickly
Concrete estimating guide
These notes explain practical concrete estimating without repeating the calculator result.
Cubic feet vs cubic yards
Small calculations often start in cubic feet, while ready-mix concrete is usually ordered in cubic yards.
Why slab thickness matters
Thickness directly changes volume. A small thickness change across a large slab can add significant concrete.
Ready-mix concrete vs bagged concrete
Bagged concrete can work for small jobs. Ready-mix delivery is often more practical for larger pours.
Measuring tips before ordering
Measure inside the forms, check depth in several spots, and confirm the base is compacted and level where needed.
Safety and project planning reminders
Structural projects may require local code checks, reinforcement, drainage planning, and professional guidance.
Formula
Rectangular Volume = Length × Width × Thickness
Circular Volume = π × Radius² × Thickness
Cubic Yards = Cubic Feet ÷ 27
Final Volume = Base Volume × (1 + Waste Buffer Percentage)
Bag Count = Final Volume ÷ Bag Yield
Variables
- Length and width describe the project footprint.
- Thickness or depth describes how deep the concrete is.
- Radius is half of diameter for circular projects.
- Bag yield is the concrete volume from one bag.
Worked example
A 10 ft by 10 ft slab at 4 in thick is about 33.33 cubic feet. Divide by 27 to get about 1.23 cubic yards before waste.
Assumptions
The calculator assumes consistent dimensions, simple shapes, and product yield based on the selected bag size.
Limitations
Concrete estimates are approximate. Measurements, formwork, compaction, base preparation, and supplier rounding can affect final needs.
Frequently asked questions
How do I calculate concrete for a slab?
Multiply length by width by thickness using the same unit system, then convert the result to cubic yards. Add a waste buffer for form variation, uneven base, and ordering safety.
How many bags of concrete do I need?
Divide the final concrete volume by the yield of one bag. Bag yield varies by product, so check the label before buying.
How much concrete is in one cubic yard?
One cubic yard equals 27 cubic feet. Ready-mix concrete is commonly ordered by the cubic yard.
Should I add extra concrete for waste?
Yes. Many projects use a waste buffer because forms, excavation depth, base level, and measuring errors can change the final amount needed.
Is ready-mix cheaper than bagged concrete?
It depends on volume, delivery fees, labor, and local prices. Small repairs may be practical with bags, while larger slabs are often easier with ready-mix delivery.
How thick should a concrete slab be?
Thickness depends on the project, soil, load, reinforcement, drainage, and local requirements. Use typical guides as a starting point, then check project specifications.
Can this calculator estimate concrete for post holes?
Yes. Select post holes, enter hole diameter, depth, number of holes, and optional post diameter to subtract the post volume.
Why is my concrete estimate different from a supplier quote?
Suppliers may round order quantities, use different waste assumptions, include delivery minimums, or account for site conditions not included in a simple calculator.
Does reinforcing steel affect concrete volume?
Reinforcement usually has a small effect on volume for common DIY estimates, but structural projects should follow drawings, codes, and professional guidance.
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