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Category Foundation & Concrete

Unit System

Structure Type

Length (ft)

Width (ft)

Thickness / Height (in)

Quantity

Concrete Grade (Ratio)

Wastage Margin (%) 5%

Pre-mix Bag Size

Price per Pre-mix Bag ($)

Total Wet Volume

0.00 yd³

0.00 m³

Pre-mix Bags Needed0
Est. Cost: $0.00

Raw Material Breakdown (Mix Your Own)

Cement 0 lbs

Sand 0 lbs

Gravel/Aggregate 0 lbs

Water (Approx) 0 gal

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About

Precise concrete estimation is the difference between a profitable job and a logistical nightmare. Underestimating volume leads to cold joints and structural weaknesses while overestimating results in wasted capital and disposal fees. This tool addresses the specific volumetric requirements of slabs, footings, and columns, adjusting for standard construction wastage protocols.

Construction professionals rely on accurate material breakdowns to procure the correct ratio of cement, sand, and aggregate. Whether mixing on-site with pre-mix bags or ordering a ready-mix truck, knowing the exact weight of materials required for specific compressive strengths (e.g., 3000 PSI vs 4000 PSI) ensures structural integrity. This calculator incorporates standard density variables and allows for customizable pricing to generate an immediate Bill of Materials.

Formulas

The core calculation determines the total volume required, including a safety margin for uneven subgrades or spillage.

Volume Calculation:

Vtotal = (L × W × D) × (1 + wastage100)

To determine the weight of individual dry materials based on the chosen mix ratio (rc:rs:ra), we use the dry volume yield factor (approx 1.54 to account for shrinkage when water is added).

Cement Weight = Vdry × Cratio × 1506TotalRatio

Reference Data

Concrete Grade	Mix Ratio (Cement:Sand:Aggregate)	Compressive Strength (28 Days)	Typical Application
C10	1 : 3 : 6	10 MPa (1450 PSI)	Patio slabs, pathways, non-structural work
C15	1 : 2.5 : 5	15 MPa (2175 PSI)	Residential flooring, kerbs
C20	1 : 2 : 4	20 MPa (2900 PSI)	Light footings, garage floors, internal slabs
C25	1 : 1.5 : 3	25 MPa (3625 PSI)	General construction, reinforced concrete
C30	1 : 1 : 2	30 MPa (4350 PSI)	Heavy-duty slabs, external driveways
C35	Design Mix	35 MPa (5000 PSI)	Structural columns, piling, heavy loads

Frequently Asked Questions

When water is added to the dry mix (cement, sand, aggregate), the particles settle into the voids, reducing the total volume by approximately 30-35%. The calculator automatically accounts for this "shrinkage factor" to ensure you order enough dry materials to fill the wet formwork.

Standard practice dictates a 5% to 10% wastage margin. However, for uneven ground (excavated earth footings), wastage can exceed 20%. Underestimating this often results in a "short pour," creating a cold joint which significantly compromises the structural strength of the slab.

It calculates both simultaneously. The tool provides the total cubic yardage/meterage for ordering a ready-mix truck, and also converts that volume into the number of 60lb/80lb (or 20kg/25kg) bags required for smaller DIY projects.

For non-load-bearing projects like walkways or patios, 2500-3000 PSI (C20) is typically sufficient. For driveways, garage floors, or foundations supporting structures, a minimum of 3500-4000 PSI (C30) is standard to prevent cracking under load and freeze-thaw cycles.