Materials Calculator
Work out how much concrete, gravel, or mulch a site needs, plus bags and estimated weight.
Site dimensions
Waste & packaging
How this is calculated
Volume is area (length × width) times depth. A waste allowance is added on top to cover compaction, spillage, and uneven ground — 10% is a reasonable default. That volume converts to an estimated weight using a typical density for the chosen material (concrete, gravel, and mulch pack very differently — mulch is mostly air by comparison), and to a bag count using the coverage-per-bag figure printed on your specific product (check the bag label — coverage varies between brands and even between bag sizes of the same brand).
Common questions
Where does the default coverage-per-bag number come from?
It pre-fills with a common real bagged-product size for the selected material — an 80 lb bag of concrete mix (0.6 cu ft, per Quikrete's published yield), a 0.5 cu ft bag of landscape gravel, or a 2 cu ft bag of mulch. Switching material updates this default automatically, but it stays editable — once you type in the coverage printed on your actual product, switching material again won't overwrite your number.
Why is the weight only an estimate?
The density used here (2400 kg/m³ for concrete, 1600 kg/m³ for gravel, 300 kg/m³ for mulch) is a typical reference value, not your specific product's exact spec — moisture content, compaction, and particle size all shift real density. Use it for a rough sense of load (can your vehicle carry it?), not a precise order quantity.
Why does the same volume need such different amounts of material by weight?
Density varies enormously by material — a cubic meter of concrete weighs about 8x as much as a cubic meter of mulch, because mulch is bulky, loosely packed organic material while concrete is dense and heavily compacted. Bag count also depends entirely on the coverage printed on your specific product, which is unrelated to weight.
Part of Home Improvement Calculators