m
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cement:sand:aggregate.
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Concrete Calculator
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This Concrete Calculator estimates the volume of concrete needed for a slab, footing, or similar pour from its length, width, and thickness, then breaks that down into cement, sand, and aggregate quantities based on your chosen mix ratio (like the common 1:2:4 nominal mix), including an estimated number of 50kg cement bags. It applies the standard 1.54× dry-to-wet volume conversion used in construction estimating, plus an adjustable wastage allowance to avoid running short on site. It's built for homeowners planning a small pour and contractors doing a quick material estimate before ordering. Everything runs locally in your browser. Scroll down to enter your dimensions and mix ratio.
Features
- Computes wet and dry concrete volume from slab dimensions
- Breaks down cement, sand, and aggregate by your mix ratio
- Estimates cement bags needed (50kg bags)
- Adjustable wastage allowance percentage
- Supports any cement:sand:aggregate ratio, e.g. 1:1.5:3 or 1:2:4
Why use this concrete calculator?
- Faster than manual dry-volume and ratio math
- Reduces the risk of under-ordering materials
- Fully private — nothing is uploaded
- Free with unlimited use
Frequently asked questions
What mix ratio should I use?
1:2:4 (cement:sand:aggregate) is a common nominal mix for general use like slabs and footings; higher-strength work may use richer ratios like 1:1.5:3 — check your local building code or engineer's spec.
Why is the dry volume larger than the wet volume?
Dry materials (cement, sand, aggregate) have air gaps between particles that get filled with water and compaction, so roughly 54% more dry volume is needed to produce a given wet/poured volume — the standard 1.54 factor accounts for this.
How many bags of cement are in a bag?
This calculator assumes standard 50kg cement bags (≈0.0347 m³ per bag), common in many regions — adjust manually if your local bag size differs.
What wastage allowance should I use?
5% is a common default for careful sites; increase it for hand-mixing or less controlled conditions where more material is typically lost.
Is this a substitute for a structural engineer's mix design?
No, this is a general estimating tool for nominal mixes; structural or load-bearing work should follow an engineer-specified mix design.