Data Source and Methodology
Primary references:
- QUIKRETE Companies. “Concrete Mix No. 1101” Product Datasheet (Yield and Coverage), 2019. View source.
- NIST Special Publication 811. “Guide for the Use of the International System of Units (SI),” 2008 (Superseding edition). View source.
Tutti i calcoli si basano rigorosamente sulle formule e sui dati forniti da questa fonte.
The Formula Explained
Mathematical formulas
Slab Volume (consistent units):
\[ V = L \times W \times T \]
US Customary conversions:
\[ T_{\text{ft}} = \frac{T_{\text{in}}}{12} \quad;\quad V_{\text{ft}^3} = L_{\text{ft}} \times W_{\text{ft}} \times T_{\text{ft}} \] \[ V_{\text{yd}^3} = \frac{V_{\text{ft}^3}}{27} \]
Metric conversions:
\[ T_{\text{m}} = \frac{T_{\text{cm}}}{100} \quad;\quad V_{\text{m}^3} = L_{\text{m}} \times W_{\text{m}} \times T_{\text{m}} \] \[ V_{\text{yd}^3} = V_{\text{m}^3} \times 1.30795 \]
Waste allowance:
\[ V_{\text{waste}} = V \times \left(1 + \frac{p}{100}\right) \]
Bag counts (using yield Y in ft³):
\[ \text{Bags} = \left\lceil \frac{V_{\text{ft}^3,\,\text{waste}}}{Y} \right\rceil \]
\[ V = L \times W \times T \]
US Customary conversions:
\[ T_{\text{ft}} = \frac{T_{\text{in}}}{12} \quad;\quad V_{\text{ft}^3} = L_{\text{ft}} \times W_{\text{ft}} \times T_{\text{ft}} \] \[ V_{\text{yd}^3} = \frac{V_{\text{ft}^3}}{27} \]
Metric conversions:
\[ T_{\text{m}} = \frac{T_{\text{cm}}}{100} \quad;\quad V_{\text{m}^3} = L_{\text{m}} \times W_{\text{m}} \times T_{\text{m}} \] \[ V_{\text{yd}^3} = V_{\text{m}^3} \times 1.30795 \]
Waste allowance:
\[ V_{\text{waste}} = V \times \left(1 + \frac{p}{100}\right) \]
Bag counts (using yield Y in ft³):
\[ \text{Bags} = \left\lceil \frac{V_{\text{ft}^3,\,\text{waste}}}{Y} \right\rceil \]
Glossary of Variables
- L (Length): Longer side of the slab. Input in feet/inches or meters.
- W (Width): Shorter side of the slab. Input in feet/inches or meters.
- T (Thickness): Slab thickness. Input in inches or centimeters.
- p (Waste %): Additional percentage to cover loss and irregularities.
- V: Volume of concrete (ft³, yd³, or m³).
- Y (Yield): Concrete volume per bag in cubic feet (e.g., 80 lb → 0.60 ft³).
- Area: Slab surface area (ft² or m²).
How It Works: A Step‑by‑Step Example
Suppose you need a 12 ft by 10 ft patio, 4 in thick, with a 10% waste allowance.
- Convert thickness to feet: 4 in ÷ 12 = 0.333 ft.
- Compute base volume: V = 12 × 10 × 0.333 = 39.96 ≈ 40 ft³.
- Apply 10% waste: 40 × 1.10 = 44 ft³.
- Convert to cubic yards: 44 ÷ 27 = 1.63 yd³.
- 80 lb bags (0.60 ft³ per bag): 44 ÷ 0.60 = 73.3 → round up to 74 bags.
Frequently Asked Questions (FAQ)
- What dimensions does this calculator support?
- Rectangular slabs. For irregular shapes, break them into rectangles, calculate each, and sum the results.
- How accurate are the bag counts?
- Bag yields are based on widely cited manufacturer data sheets (e.g., QUIKRETE). Actual yield can vary with compaction and water content. Always order a bit extra.
- Should I use 4 inches or 6 inches?
- Walkways/patios are commonly 4 in. Driveways and heavier loads often require 4–6 in. Always follow local codes and soil conditions.
- Does adding reinforcement change how much concrete I need?
- No. Rebar or mesh is volumetrically negligible for ordering purposes.
- What’s the difference between ready‑mix and bagged concrete?
- Ready‑mix is delivered by truck and priced per cubic yard. Bags are convenient for small jobs but involve more labor and may cost more per yard.
- Can I switch units after entering values?
- Yes. Switching between US and Metric converts the values and preserves your inputs.