Inputs
System: Imperial (ft / in)Switch units anytime; values persist per row.
Includes spillage, uneven subgrade, edges, and over-excavation.
Used to estimate material cost for selected bag size.
Areas (Rectangular)
| # | Length | Width | Thickness | Units | Volume |
|---|
Imperial: length/width in feet, thickness in inches. Metric: length/width in meters, thickness in centimeters.
Auto-fills from size. Adjust if your brand differs.
40 lb ≈ 0.30 ft³
50 lb ≈ 0.375 ft³
60 lb ≈ 0.45 ft³
80 lb ≈ 0.60 ft³
90 lb ≈ 0.675 ft³
| Bag Size | Yield (ft³) | Bags Required |
|---|
Example Data
Common slab dimensions at 4 in thickness, 10% waste, 60 lb bags.
| Slab | Length (ft) | Width (ft) | Thickness (in) | Volume (ft³) | Bags @60 lb |
|---|---|---|---|---|---|
| Patio | 10 | 12 | 4 | ||
| Driveway Section | 12 | 16 | 4 | ||
| Garage | 24 | 24 | 6 |
Formulas Used
- Rectangular volume: \( V = L \times W \times T \)
- Imperial inputs: L, W in feet; T in inches ⇒ \( V_{ft^3} = L_{ft} \times W_{ft} \times \frac{T_{in}}{12} \)
- Metric inputs: L, W in meters; T in centimeters ⇒ \( V_{m^3} = L_{m} \times W_{m} \times \frac{T_{cm}}{100} \)
- Unit conversion: \( 1\,m^3 = 35.3146667\,ft^3 \), \( 1\,yd^3 = 27\,ft^3 \)
- Waste allowance: \( V_{adj} = V \times (1 + \frac{\text{waste}\%}{100}) \)
- Bags required: \( \text{Bags} = \lceil \frac{V_{ft^3}}{\text{yield per bag (ft}^3)} \rceil \)
Yields vary by brand; adjust "Yield per Bag" to match your product data.
How to Use
- Select your measurement system.
- Add one or more rectangular areas representing the slab footprint.
- Enter length, width, thickness per area using the shown units.
- Choose waste percentage for contingencies.
- Select bag size; adjust yield per bag if your brand differs.
- Optionally enter cost per bag to estimate material cost.
- Click Recalculate to update totals and bag counts.
- Export your results to CSV or PDF for recordkeeping.
Tips & Guidance
- For 4 in slabs, many projects target 3000–4000 psi mixes.
- Consider control joints at 24–36 times slab thickness.
- Compacted subgrade and consistent forms reduce overuse and waste.
- Mesh or rebar needs are project-specific; consult local codes.
FAQs
Estimates depend on inputs, selected yields, and waste. Brand yields and site conditions vary; include an appropriate contingency.
The tool calculates per size. You can run multiple scenarios and combine results as needed on site.
Use the product bag’s stated yield. Defaults are typical for premix; override “Yield per Bag” to match your brand.
Approximate complex shapes by adding multiple rectangles that partition the slab footprint.
Total volume is multiplied by (1 + waste/100) before converting to bag counts.
Enter a unit price per bag. The tool multiplies by the required bags for the selected size.
Disclaimers
This calculator is for planning only. Verify mix requirements, reinforcement, and placement practices with local codes and a qualified professional.