Compost Requirement Calculator

Work out compost requirement instantly with clear inputs, formula shown and shareable results.

About Compost Requirement Calculator

Compost is ordered by weight but hauled and spread by volume, so the tonnage (area x rate) is converted through bulk density to cubic metres. Dividing that volume by the area gives the spread depth in millimetres, which is the figure to check against what a spreader can lay down in one pass.

Formulas

Compost quantity

Tonnes = area (ha) x rate (t/ha); volume (m3) = tonnes x 1000 / bulk density

Spread depth

Depth (mm) = volume (m3) / area (m2) x 1000

Worked example

With the default values below, Compost Requirement Calculator returns Compost Required of 10.00. Change any input above and every figure here is recalculated in your browser.

Inputs used

Areaminimum 0.01 ha: 1 ha
Compost Application Rateminimum 0.1 t/ha: 10 t/ha
Compost Bulk Densityminimum 100 kg/m3: 550 kg/m3
Compost Priceminimum 0 per tonne: 3,000 per tonne

Results

Compost Required: 10.00
Volume Required: 18.18
Compost Cost: $30,000.00
Spread Depth: 1.82

Step by step

1Values used
2Compost quantity
3Spread depth
4Compost Required= 10.00
5Volume Required= 18.18
6Compost Cost= 30,000.00
7Spread Depth= 1.82

Assumptions and limits

The result is derived only from the 4 inputs listed above. Anything not among them is not part of the calculation.
In particular, this calculator does not take inflation, tax, fees or charges or compounding frequency into account.
Figures are rounded for display to 2 decimal places, so totals built from several rounded parts can differ slightly from the unrounded arithmetic.

How these calculators are built and tested is described on the Methodology page. If a figure looks wrong, please report it.

Frequently Asked Questions

What application rate should I use?

5-10 t/ha annually is a maintenance rate for arable soils; 20-40 t/ha is used to build organic matter on degraded land or in horticulture. Match it to a compost analysis so nutrients are not over-applied.

Should compost replace mineral fertiliser entirely?

Not immediately. Compost releases nutrients slowly and its nitrogen availability in year one is often under 15%. Use it to build soil and reduce mineral rates gradually as organic matter rises.