Concrete Calculator
Plan concrete volume, ready-mix quantity, bag requirements, material-only cost and thickness scenarios across multiple project sections.
- No signup
- Live estimate
- Transparent formulas
- 1 Calculate
- 2 Understand
- 3 Compare
- 4 Decide
Your inputs
Build your concrete project
Add each slab, footing pad or known-area section. Every section keeps its own thickness.
Used for currency, terminology and default units.
Adds only the selected extra volume after the calculated project volume.
Thickness scenariosCompare 4 uniform depths
Project estimate
Concrete required
Estimated order volume
3.889yd³
Includes your selected planning allowance. Confirm ordering and rounding with your supplier.
Project totals
- Calculated project volume
- 3.704 yd³
- Planning allowance volume
- 0.185 yd³
- Metric equivalent
- 2.973 m³
- Exact bag equivalents
- 175
- Whole bags to purchase
- 175
Confirm dimensions, product yield, mix requirements, supplier rounding and delivery constraints. This is a quantity estimate, not structural design.
Section breakdown
| Option | Shape | Area | Base volume |
|---|---|---|---|
| Main slab | Rectangle | 300 ft² | 3.704 yd³ |
Ready-mix and bag comparison
| Option | Order quantity | Calculation basis | Material-only cost |
|---|---|---|---|
| Ready-mix | 3.889 yd³ | Price per yd³ | Not entered |
| Bagged concrete | 175 exact / 175 whole bags | QUIKRETE Concrete Mix — 80 lb; yield per bag | Not entered |
Thickness scenario comparison
| Option | With allowance (yd³) | Whole bags |
|---|---|---|
| 3 in | 2.917 | 132 |
| 4 in | 3.889 | 175 |
| 5 in | 4.861 | 219 |
| 6 in | 5.833 | 263 |
Increasing thickness from 3.00 to 6.00 in increases concrete quantity by 100.0%.
Methodology
How it works
Normalize each simple section geometry to cubic metres, sum base volume, add only the selected planning allowance, then calculate ready-mix cost and bag equivalents from user-controlled price and yield.
V = area × thicknessRectangles use L × W; circles use π × (D ÷ 2)². Volumes are normalized, summed, then the selected allowance is applied.
- 1
Normalize each section
Convert rectangle, circle, or known-area dimensions and thickness to SI units.
- 2
Sum project volume
Add every independently calculated section volume.
- 3
Apply planning allowance
Add only the extra percentage selected by the user.
- 4
Calculate material options
Use entered ready-mix price and actual product yield per bag when provided.
- 5
Compare scenarios
Apply each selected uniform thickness to the same combined section area.
Method reviewed August 2026
Transparent arithmetic
All formulas
- V = L × W × T
- rectangular volume using the documented inputs.
- V = π × (D ÷ 2)² × T
- circular volume using the documented inputs.
- V = A × T
- volume using the documented inputs.
- O = V × (1 + p ÷ 100)
- estimated order volume using the documented inputs.
- B = O ÷ Y
- exact bag equivalents using the documented inputs.
- P = ceil(B)
- whole bags to purchase using the documented inputs.
- Cᵣ = O × r
- ready-mix material cost using the documented inputs.
- Cᵦ = P × b
- bagged material cost using the documented inputs.
Important context
Estimate assumptions
- Planning allowance
- User selected Extra volume added after calculated project volume.
- Bag calculation
- Volume yield per bag Bag mass alone is never used to calculate quantity.
- Pricing
- User supplied No delivery, tax, labor, or current market price is assumed.
Worked example
20 ft × 15 ft slab
At 4 in thickness, base volume is 100 ft³ (3.704 yd³). A 5% allowance produces 105 ft³, or 3.889 yd³. At 0.60 ft³ yield per bag, that is 175 exact equivalents and 175 whole bags.
Before ordering
Concrete checklist
- Recheck each dimension and thickness.
- Confirm mix/strength and actual product yield.
- Ask about minimum orders, short-load charges, delivery access and supplier rounding.
- Account separately for tax, delivery, labor, pumping and reinforcement.
Scope
Quantity planning, not concrete design
This tool does not choose thickness, strength, reinforcement, joints, subgrade, curing method or code compliance. Seek qualified project advice where required.
Questions
Concrete calculator FAQ
Why use yield rather than bag weight?
Yield is the fresh-concrete volume produced; package mass alone does not define that volume.
Does cost include delivery or labor?
No. Comparisons use only the prices you enter for ready-mix material and bags.
Why round bags up?
You purchase whole bags, so the exact equivalent is rounded upward with the ceiling function.
Can sections have different thicknesses?
Yes. Each project section has its own thickness; scenarios intentionally apply one uniform thickness for comparison.
References
Methodology and product-yield sources
- Concrete Craftsman Series: Slabs-on-Ground — American Concrete InstituteReviewed August 2026
Supports dimensional volume calculation and supplier ordering considerations.
- What is yield? — American Concrete InstituteReviewed August 2026
Defines concrete yield as produced fresh-concrete volume.
- QUIKRETE Concrete Mix Technical Data — QUIKRETE · 2025Reviewed August 2026
Supports approximate yields of 0.30, 0.45, and 0.60 ft³ for 40, 60, and 80 lb QUIKRETE Concrete Mix bags.