How to estimate aggregate
Measure the area and intended finished depth before choosing a bag size
Back to calculator ↑Measure the area
Measure length and width in metres. Break irregular areas into rectangles and add them. Use intended layer depth rather than the height of a loose pile.
Trace only the surface that will receive aggregate, excluding planters, steps and planting beds. If a path changes width, divide it into measured sections and add their areas. Check existing levels in several places: hollows and slopes change the fill compared with a flat rectangle. Enter site measurements rather than relying solely on a drawing.
Choose the depth
Enter the intended finished or compacted layer in millimetres. Suitable depth depends on the use and subgrade; this tool does not specify an engineered layer.
The example 50 mm is the desired finished layer and becomes 0.05 m before multiplication. Decorative cover, pedestrian paths and load-bearing bases need different materials and depths, so this calculator does not choose a thickness. For vehicle loads or weak ground, have the base construction and drainage checked before using the bag count as an order.
Calculate volume
The 0.75 m³ result is the geometric layer; 0.825 m³ includes the entered 10% allowance. Multiplying by 1,000 gives 825 L, which is exactly 33 bags at 25 L each. When changing bag size, divide the order litres by the new bag volume and round up again. Rescaling an already rounded bag count can give the wrong purchase quantity.
Check before ordering
Ask the supplier whether stated bag volume is loose or compacted yield, and confirm aggregate grading for the job. An entered price covers material only.
A bag volume does not itself state mass. Density varies with stone type, grading and moisture, so do not guess kilograms from litres. For bulk tonnes or truckloads, ask the supplier for the specific product density and loose-to-finished yield. Confirm vehicle access and unloading space, and consider staged deliveries if one large pile would obstruct the work.
Common questions
How do I convert millimetres?
Enter 50 in the millimetre field; the calculator converts it to 0.05 m. Make sure it is the intended finished layer rather than the depth of one isolated hollow.
Why add allowance?
Allowance covers measurement and spreading variation, but is not a universal compaction factor. For loose bulk aggregate, ask the supplier about finished yield.
What is a 25 L bag in cubic metres?
Since 1 m³ equals 1,000 L, divide 25 by 1,000. This volume does not state bag mass because aggregate density varies by product.
Sources and calculation guidance
Check these against your chosen product’s label and instructions.