How much extra concrete should I order?

Order 10% extra for waste, spillage, and minor surface variations. For large projects or complex shapes, consider 15% extra.

What is the right mix ratio for my project?

For general use (foundations, slabs): 1:2:3. For high strength: 1:1.5:3. For screed/finish: 1:2:4. Add fiber or steel reinforcement for added strength if needed.

How long does concrete take to cure?

Initial set takes 24-48 hours. Concrete reaches 70% strength in 7 days and full strength in 28 days. Keep it moist during curing for best results.

What is M20 concrete and why does this calculator use it?

M20 refers to a concrete mix that achieves a compressive strength of 20 N/mm² at 28 days. It uses a 1:1.5:3 ratio of cement, sand, and coarse aggregate. This grade is widely used for residential slabs, beams, and columns, making it a practical default for most general-purpose projects.

How many bags of cement do I need per cubic meter of concrete?

For a standard M20 mix, approximately 8 bags of 50 kg cement are required per cubic meter of concrete. This figure can vary slightly depending on the water-cement ratio and the grading of your aggregates, so always confirm with your mix design or supplier.

Can I use this calculator for a round column or circular slab?

This calculator is designed for rectangular sections (length × width × depth). For a round column, calculate the volume manually using the formula: Volume = π × radius² × height, then use the material ratios from this calculator to determine how much cement, sand, and gravel you need.

What happens if I add too much water to the concrete mix?

Excess water increases the water-cement ratio, which reduces the final strength and durability of the concrete. A mix that looks very fluid or soupy is likely too wet. The standard water-cement ratio for M20 concrete is approximately 0.5, meaning 0.5 liters of water per kilogram of cement.

Concrete Volume Calculator - Bunny Calculator

Complete User Guide

Our Concrete Calculator helps you estimate materials for projects. Here's how to use it:

Step 1: Select your project type: slab, column, foundation, or custom shape.

Step 2: Enter dimensions (length, width, depth/height) in meters or feet.

Step 3: For multiple structures, enter the quantity.

Step 4: Click 'Calculate' to see total concrete volume needed.

The calculator displays: - Volume in cubic meters and cubic feet - Estimated pre-mix bags needed - Raw materials for on-site mixing (cement, sand, gravel) - Recommendation for 10% extra for waste

The Mathematical Formula

Volume = Length × Width × Depth

Concrete volume calculations:

Slab: Volume = Length × Width × Thickness

Column (round): Volume = π × radius² × height

Standard concrete mix (1:2:3 ratio): - 1 part cement - 2 parts sand - 3 parts aggregate gravel - 0.5 parts water (water-cement ratio)

1 cubic meter of concrete ≈ 7-8 bags of cement (50kg each)

About Concrete Volume Calculator

The Concrete Volume Calculator estimates how much concrete you need for a given structure and breaks down the raw materials required based on a standard M20 mix ratio (1:1.5:3). Whether you are planning a floor slab, a column, a foundation, or any rectangular pour, entering the length, width, and depth gives you the total volume in both cubic meters and cubic feet — so you can order or mix the right amount from the start.

Concrete is a composite of cement, sand (fine aggregate), coarse aggregate (gravel), and water. The proportions of these components determine the final strength and workability of the mix. The M20 grade used in this calculator — one of the most common grades for residential and light commercial work — refers to a design mix that achieves a characteristic compressive strength of 20 N/mm² after 28 days of curing.

Why accurate volume estimation matters: Ordering too little concrete can lead to cold joints — visible and structurally weak seams that form when a fresh pour is placed against partially hardened concrete. Ordering too much wastes money and creates disposal challenges. A 10% buffer over your calculated volume is a standard practice that accounts for spillage, surface leveling, and minor form imperfections.

The material quantities shown — bags of cement (50 kg each), cubic feet of sand, and cubic feet of gravel — give you a reliable starting point for on-site batching. Always verify against your local concrete supplier's specifications, as minor variations in aggregate size and moisture content can affect the final quantities needed.

Frequently Asked Questions

Concrete Volume Calculator