About

Concrete mixing requires precision; guessing ratios leads to structural weakness or crumbling surfaces. This calculator computes the exact volume of your slab or footing and decomposes it into the required dry materials based on standard construction ratios (e.g., C20, C25). Uniquely, it translates these dry weights into practical construction units like "Buckets" or "Shovels", addressing the reality that most DIYers and small contractors do not weigh materials on site. It accounts for the 'Shrinkage Factor'-dry volume loses roughly 30-35% of its bulk when water is added.

Formulas

To produce 1 m³ of wet concrete, roughly 1.54 m³ of dry material is required due to void filling. The formula for the Cement Volume is:

V_cement = V_wet × 1.54∑ Parts × Part_cement

Material Weight is calculated using standard densities:

Weight = Volume × Density

Typical Densities: Cement (1440 kg/m³), Sand (1600 kg/m³), Gravel (1500 kg/m³).

Reference Data

Mix Type	Ratio (Cement:Sand:Agg)	Application
C15 (General)	1 : 3 : 6	Non-structural, patio bases, kerbs.
C20 (Standard)	1 : 2 : 4	Internal floors, garage bases, paths.
C25 (Strong)	1 : 1.5 : 3	Foundations, footings, external driveways.
C30 (Structural)	1 : 1 : 2	Heavy duty, reinforced beams/columns.

Frequently Asked Questions

Dry materials (sand/gravel) contain air gaps. When you add water and cement, these fine particles fill the voids in the gravel. Therefore, to get 1 cubic meter of finished wet concrete, you need approximately 1.54 cubic meters of dry ingredients. Ignoring this leaves you short on material.

A C25 mix (1:1.5:3) or C30 mix is recommended for driveways to withstand vehicle weight and freeze/thaw cycles. The standard C20 (1:2:4) is often too weak for heavy traffic.

It is an approximation for sites without scales. We assume a standard 'Builder's Shovel' holds roughly 4-5kg of sand/gravel. Always measure volume (using buckets) for critical structural mixes rather than relying solely on shovel counts.