TryBuildCalcSlab Concrete Calculator in Feet (RCC Volume, Cement, Sand & Aggregate)
Calculate slab concrete volume and materials.
Calculate slab concrete materials when length and width are entered in feet. Adjust slab dimensions, thickness, mix ratio, and wastage for your RCC estimate.
🕒 Last updated: August 6, 2026
Inputs
ℹ️Typical: 100–150 mm
Optional Deductions
Deduct staircase openings, ducts, lift shafts, or other voids from the slab area before calculating concrete volume.
Cost
Concrete Volume: 3.540 m³ / 125.0 cft
Wet Volume: 3.540 m³ / 125.0 cft
Dry Volume: 5.451 m³ / 192.5 cft
Sand: 1.487 m³ / 52.5 cft
Aggregate: 2.973 m³ / 105.0 cft
Cement Required (Including 5% Wastage): 30 bags
Extra (Wastage): 1.43 bags
Planning the shuttering and prop layout for this slab? Slab Shuttering Process Guide →
Approximate results for planning only. Verify with a professional.
Looking for the verification checklist, reference tables, tips, or common mistakes?See the complete Concrete Slab Calculator.
Slab concrete from feet and inches
This page is useful when slab dimensions are measured in feet and inches.
The calculator is pre-filled for this slab use case. Edit any input and the worked example updates from the active values.
- Default slab: 20 ft x 15 ft.
- Thickness: 5 in.
- Converts to cubic meters.
How does the concrete slab calculator work?
The calculator follows standard civil engineering formulas to estimate concrete volume and material quantities step-by-step, from the net slab area down to cement bags.
Step 1 — Calculate Net Slab Area
For a single rectangular slab this is just Length × Width. Multiple Sections sums each rectangle (for L-shaped/irregular footprints); Optional Deductions subtracts any staircase, duct, or void areas.
Step 2 — Calculate Wet Volume
Step 3 — Convert to Dry Volume
The factor 1.54 accounts for voids, bulking of sand, and material losses during mixing.
Step 4 — Calculate Material Proportions
Step 5 — Convert Cement Volume to Bags
Step 6 — Add Wastage
Step 7 — Cost (Optional)
All three quantities are priced at their wastage-adjusted amount. Sand and aggregate prices can be entered per m³ or per cft — whichever unit you enter is converted to match automatically.
Worked Example: Concrete Slab Calculation
This example uses the active inputs above and follows the same steps as the Formula section.
Input Values Used
| Input | Value |
|---|---|
| Length × Width | 20 ft × 15 ft = 27.871 m² |
| Thickness | 5 in (0.127 m) |
| Concrete Mix | M20 (1:1.5:3) |
| Wastage | 5% |
Step 1 — Net Area & Wet Volume
| Calculation | Substitution | Result |
|---|---|---|
| Net Area = Gross − Openings | 27.871 − 0 | 27.871 m² |
| Wet Volume = Net Area × Thickness | 27.871 × 0.127 | 3.54 m³ / 125.0 cft |
Step 2 — Dry Volume
| Calculation | Substitution | Result |
|---|---|---|
| Dry Volume = Wet Volume × 1.54 | 3.54 × 1.54 | 5.451 m³ / 192.5 cft |
Step 3 — Materials & Cement Bags
| Material | Share of Mix (1:1.5:3) | Result |
|---|---|---|
| Sand | 1.5 / 5.5 | 1.487 m³ / 52.5 cft |
| Aggregate | 3 / 5.5 | 2.973 m³ / 105.0 cft |
| Cement Bags (with 5% wastage) | 1 / 5.5 | 30 bags |
Therefore, this slab needs approximately 3.54 m³ / 125.0 cft of concrete, requiring 30 cement bags, 1.487 m³ / 52.5 cft sand, and 2.973 m³ / 105.0 cft aggregate (including 5% wastage on cement).
Cross-check against the Standard Concrete Mix Ratios table in the complete Concrete Slab Calculator.