Concrete Calculator
Calculate the volume of concrete needed for slabs, footings, columns, or steps. Get results in cubic metres, cubic feet, and bags of ready-mix.
Did this tool work for you?
How to use this calculator
Volume in cubic metres (m³). A standard 25 kg bag of ready-mix concrete covers approximately 0.012 m³; a 40 kg bag covers 0.019 m³.
- 1
Enter the length, width, and depth of your concrete slab or footing in metres.
- 2
A 10% waste allowance is standard — increase for complex shapes.
- 3
Bag counts assume standard pre-mix concrete bags; adjust for your supplier's bag size.
Frequently asked questions
How thick should a concrete slab be?
Residential driveways: 100–150 mm. Garage floors: 100 mm. Footpaths: 75–100 mm. Structural slabs and commercial floors: 150–200 mm. Always check local building codes and soil conditions.
How many bags of concrete do I need?
A 25 kg bag of standard pre-mix concrete yields about 0.012 m³ when mixed. For 1 m³ you need approximately 85 bags. Ordering ready-mix truck concrete is more economical for volumes above 0.5 m³.
What is a good concrete mix ratio?
A general-purpose mix is 1 part cement : 2 parts sand : 3 parts aggregate (1:2:3 by volume). For stronger concrete (driveways, structural): 1:1.5:3. Always add the minimum water needed — excess water weakens concrete.
Concrete Calculator — Slabs, Footings & Bag Counts
How to use the concrete
Use this concrete to he volume of concrete needed for slabs, footings, columns, or steps. Enter your values above and get your result in seconds. The tool is free, works on all devices, and keeps your data private — nothing is stored or shared.
How the concrete works
The concrete calculator uses standard formulas used in building projects, renovation planning, and material ordering. Enter your inputs, and the tool calculates the result instantly in your browser. No server-side processing means your data stays on your device. Results update in real time as you change inputs.
When to order ready-mix vs bags
For small pours under 0.5 m³ (e.g., fence posts, small pads), bagged pre-mix is more practical. For volumes above 0.5–1 m³, ordering ready-mix concrete by truck is faster, stronger (quality-controlled mix), and often cheaper per m³ despite the minimum delivery charge.
Curing concrete properly
Concrete gains most of its strength in the first 28 days. Keep it moist for at least 7 days (cover with wet hessian or plastic sheeting) and avoid foot traffic for 24 hours, vehicle traffic for 7 days. Temperature affects curing: avoid pouring below 5°C or above 35°C without special precautions.
Concrete: how it works
Construction estimation tools save time and reduce material waste by calculating exact quantities before you buy. This tool uses standard industry formulas for accurate estimates across common building and renovation tasks.
Who uses this tool?
Contractors, DIY homeowners, quantity surveyors, and architects use it to generate material lists before requesting quotes. It supports better project planning and reduces the risk of costly underestimates.
Learn more from an authoritative source:
WikipediaPaint Calculator
Calculate how many litres of paint you need to cover walls, ceilings, or a room. Accounts for doors, windows, coats, and paint coverage rate.
Flooring Calculator
Calculate how many square metres of flooring you need for any room. Supports rectangular and L-shaped rooms, with waste percentage.
Tile Calculator
Calculate how many tiles you need for a floor or wall. Enter room dimensions and tile size to get tile count, boxes needed, and grout quantity.
Fence Calculator
Calculate the number of fence posts, rails, pickets, and panels needed for any fence length. Supports common picket and panel fence styles.
Results are estimates for informational purposes only and do not constitute professional financial, medical, legal, or technical advice. Read full disclaimer →