RCC Slab Calculator

Quick material estimation for RCC slabs — Indian Standards IS 456:2000

Quick Presets

Slab Area (Sq Ft)Enter total floor area of the slab (including all floors if multi-level)

Slab Thickness (mm)Common: 150mm for residential, 200mm for commercial

Concrete Grade (IS 456)M20: General residential | M25: Better durability | M30: High load

Waste Factor: 5%Accounts for breakage, spillage, and site waste

Thumb Rule (Quick Check)

Steel ≈ 1% of concrete volume
For M25 slab: 0.05–0.07 bags cement/sqft
Expected steel: 3.5–4.5 kg/sqft

Click "Calculate" to see material estimates.

Concrete Grade Selection: Choose based on durability and load requirements. M25 is standard for most residential work in India. Higher grades (M30+) for commercial, exposed, or heavy-load areas.
Slab Thickness Thumb Rule: L/d ratio typically 20-30. For 4m span with L/d=25: d=160mm. Minimum 100-125mm for residential per IS 456:2000 Clause 23.2.
Reinforcement Ratio: IS 456 specifies minimum 0.15% (0.12% for HYSD) and maximum 4% of cross-sectional area. Typical practice: 0.75-1% for slabs.
Concrete Cover: Protects steel from corrosion. Mild exposure (indoor, non-aggressive): 20mm. Moderate/Severe: 30-40mm. Clause 26.4 of IS 456.
Unit Weight of RCC: 25 kN/m³ (2500 kg/m³) used for self-weight calculations in design.
Mix Design: Cement-Sand-Aggregate ratios shown are nominal. Actual design should account for aggregate quality, water-cement ratio, and curing conditions.
Waste Factor: 5% is standard for site conditions in India. Accounts for breakage during transport, formwork contact loss, and spillage.
Curing Period: Minimum 7 days wet curing (IS 456 Clause 9.3). Critical for strength development and crack control.
Deflection Control: Span/deflection ≤ 250 for live loads, ≤ 350 or 20mm for total (whichever is less). Adequate depth selection prevents excessive deflection.
Cost Estimate: Concrete: ₹6,500-8,500/cu.m (2026, incl. labor) in metros. Steel: ₹60-75/kg. Sand: ₹800-1200/cu.m. Vary by location & market conditions.

Concrete Grade	Ratio (C:S:A)	Compressive Strength	Cover (Top)	Cover (Bottom)	Reinforcement
M20	1:2:4	20 MPa	20mm	20mm	12mm @ 150mm c/c
M25	1:1.5:3	25 MPa	20mm	20mm	12mm @ 150mm c/c
M30	1:1:2	30 MPa	25mm	25mm	12mm @ 150mm c/c
M35	1:1.19	35 MPa	30mm	30mm	12mm @ 100mm c/c
M40	1:0.8:1.6	40 MPa	30mm	30mm	16mm @ 100mm c/c

Component	Details	Notes
Main Bars	12mm TMT @ 150mm c/c (Both ways)	Can be adjusted based on load and span. Clause 26.5.2
Distribution Bars	8mm @ 200mm c/c (perpendicular)	Prevents shrinkage & temperature cracks. Min 0.15% area
Spacing Limits	Max = Slab thickness or 300mm (whichever is less)	Clause 26.3.4 of IS 456:2000
Nominal Cover	15-20mm bottom, 15-20mm top	Based on bar diameter and exposure. Clause 26.4
Effective Depth (d)	Thickness - Cover - (Bar dia / 2)	Used for shear & deflection checks