How Many Bags for 1 Square Metre of Concrete?
Concrete volume depends on three dimensions, not just area. One square metre of concrete requires vastly different material quantities depending on thickness. This guide clarifies the relationship between area, thickness, and concrete requirements.
The Missing Dimension
When someone asks about "one square metre of concrete," they usually mean a slab one metre by one metre at some assumed thickness. The standard assumption is 100mm depth, which is typical for paths, patios, and shed bases in Australia. At this thickness, 1m² requires 0.1 cubic metres of concrete.
Bag Count at Standard Thickness
For one square metre at 100mm thick, you need 11 bags of 20kg concrete mix (0.1m³ × 108 bags). This modest quantity is readily managed as a simple DIY project. The same area at different thicknesses requires proportionally different quantities.
Thickness Variations
At 75mm (paths): 8-9 bags per square metre. At 100mm (standard): 11 bags per square metre. At 125mm (driveways): 14 bags per square metre. At 150mm (heavy duty): 17 bags per square metre. Choose thickness based on intended use, not arbitrary preference.
Area-Based Planning
For larger areas, multiply square metres by the per-square-metre bag count for your chosen thickness. A 10 square metre patio at 100mm needs approximately 110 bags. Our calculator handles these conversions automatically when you enter length, width, and depth.
Why We Calculate by Volume
Professional concrete work always uses volume (cubic metres) rather than area because thickness is variable and critical. Ordering ready-mix in cubic metres, calculating reinforcement for volume, and estimating labour all depend on accurate volume figures rather than just surface area.
Practical Application
For most planning purposes, remember that each square metre at 100mm thickness needs roughly 11 bags. This quick mental calculation helps assess project scale when you're measuring areas. For precise ordering, use our calculator with exact dimensions to avoid shortfalls or excess.