Concrete Calculator

Free Concrete Calculator – Estimate Concrete Volume for Slabs, Footings, and Columns

Ordering the right amount of concrete is one of those things that looks simple and turns out to be surprisingly easy to get wrong. Order short and your pour is incomplete — a serious problem when working with ready-mix that has a limited working time and cannot be paused. Order too much and you are either disposing of surplus concrete or paying a waste surcharge. This free concrete volume calculator gives you an accurate estimate for slabs, footings, columns, and other standard pours so you can order with confidence and avoid expensive mistakes.

How Concrete Volume Is Calculated

Concrete volume is measured in cubic metres (m³). The formula depends on the shape of the element you are casting:

• Slab or pad: Length × Width × Depth (all in metres)
• Column or post: π × radius² × height
• Strip footing: Length × Width × Depth
• Drive or path: Total area × slab depth

The calculator handles the geometry automatically. Enter your dimensions in the units you are working with and it converts and computes the volume in m³, along with a weight estimate based on standard concrete density (approximately 2,400 kg/m³ for general-purpose concrete mixes).

How to Use the Concrete Calculator

1. Choose the shape of the element you are pouring from the options provided.
2. Enter the dimensions — length, width, and depth or height — in the fields shown.
3. Get an instant volume estimate in cubic metres.
4. Add a 5–10% overage to account for uneven subgrade, minor spillage, and form imperfections.

Bagged Concrete vs Ready-Mix — Which Should You Use?

For small volumes under approximately 0.5 m³, mixing by hand or with a small drum mixer is often more practical than ordering ready-mix. Ready-mix trucks typically have a minimum load charge and a small-load surcharge that makes them expensive at low volumes. Above 1 m³, ready-mix almost always makes more sense — it is more consistent, arrives ready to pour, and is faster to place than hand-mixing bag after bag.

• Bagged concrete: A 20 kg bag of general-purpose concrete mix yields approximately 0.009 m³ when mixed. For 1 m³ you would need roughly 110 bags. At 25 kg per bag you need around 90 bags per cubic metre.
• Ready-mix: Ordered in cubic metres directly from the plant. Common residential mixes include C20 (for non-structural slabs and landscaping), C25 (house foundations and general construction), and C30 (driveways and exposed slabs).

Common Projects This Calculator Is Used For

• Garden shed and garage floor slabs
• Driveway, path, and patio concrete pours
• House extension and new build foundation footings
• Fence post and gate post base holes
• Structural columns and in-situ retaining walls
• Swimming pool surrounds and base slabs
• Concrete steps and entrance platforms

Key Tips Before You Pour

• Always compact and level the subgrade before pouring a slab — an uneven base is the primary cause of cracking
• Use reinforcing mesh (A142 or A193) or rebar in any structural slab or footing
• In hot or windy weather, cover fresh concrete with wet hessian or polythene to slow evaporation and prevent plastic shrinkage cracking
• Do not pour concrete if overnight temperatures are forecast to fall below 5°C without taking additional precautions
• Allow at least 28 days for concrete to reach its full design strength before applying structural loads
• Include expansion joints in any slab longer than 4–5 metres to control cracking as the concrete expands and contracts

Getting the volume right before you order is the single most important step in planning any concrete project. Use this calculator, apply your overage, and order with the confidence that you have the right amount to complete the job without a costly mid-pour shortfall.