Soil Calculator
Calculate how many cubic meters and bags of soil you need for a bed, lawn or raised bed, based on length, width and depth.
Density and bag size are editable example values, not specifications for your product. Allowance starts at 0%; ask the supplier about compaction.
Measure the space, then choose the product
- Measure the inside length and width in metres and the layer depth in centimetres. For an irregular area, calculate separate rectangles and add their volumes.
- Enter the supplier's loose bulk density and litres per bag. The defaults are examples; soil composition and moisture change the weight.
- Set an explicit allowance if needed. The calculator shows the geometric volume separately from the quantity including your allowance, and rounds purchases up to whole bags.
What the numbers mean
Order volume = volume × (1 + allowance ÷ 100)
Weight in metric tonnes = order volume × bulk density in kg/m³ ÷ 1,000. One metric tonne (t) is 1,000 kg, not a US short ton. Bag count = order volume × 1,000 ÷ litres per bag, rounded up.
Example: 40-litre bags for a raised bed
A 3 × 1.5 m bed filled 30 cm deep needs 1.35 m³, or 1,350 litres, before allowance. With 40-litre bags this is 33.75 bags, so buy 34. A chosen 10% allowance makes 1,485 litres and 38 bags. At the example density of 750 kg/m³, the latter quantity weighs about 1.114 t.
Allowance is not the same as volume loss
A 20% increase in your order and a 20% reduction during settling are different calculations. If a supplier specifies that the finished volume is 80% of the loose volume, divide the finished volume by 0.8: the required allowance is 25%. This is a mathematical example, not a recommendation for your material. Do not apply compaction twice if the supplier's conversion already includes it.
Frequently asked questions
Do I need gravel under the soil?
Not as a general drainage fix in a container. Water can collect in soil above a gravel layer. Use suitable growing media and drainage openings; open-bottom beds require assessment of the ground underneath. See Illinois Extension on container drainage.
Why does changing density not change the bag count?
Soil bags here are measured in litres. Density changes the weight estimate, not the volume needed or litres per bag.