Compost Rate

Free Compost Rate calculator with clear step-by-step results.

About Compost Rate

Compost is sold by volume but spread by depth, so the starting point is area times depth. Multiplying by bulk density gives the mass you actually have to shift, and restating the same figure as tonnes per hectare lets you compare a garden dressing against agronomic guidance.

Formulas

Volume required

Volume m3 = area m2 x depth mm / 1000

Field rate

Tonnes per hectare = (mass kg / area m2) x 10,000 / 1000

Worked example

With the default values below, Compost Rate returns Compost volume needed of 1.500. Change any input above and every figure here is recalculated in your browser.

Inputs used

Area to be dressedminimum 0.1 m2: 60 m2
Application depthaccepts 1–200 mm: 25 mm
Compost bulk densityaccepts 100–1,200 kg/m3: 550 kg/m3
Bag sizeminimum 1 L: 50 L

Results

Compost volume needed: 1.500 m3
Mass to move: 825.0 kg
Bags required: 30.0 bags
Equivalent field rate: 137.50 t/ha

Step by step

1Values used
2Volume required
3Field rate
4Compost volume needed= 1.500 m3
5Mass to move= 825.0 kg
6Bags required= 30.0 bags
7Equivalent field rate= 137.50 t/ha

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 3 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

How thick should a compost dressing be?

Ten to fifteen millimetres as an annual mulch on established beds, and 25-50 mm when improving a new bed before planting. Deeper than that risks smothering shallow roots.

Why does bulk density vary so much?

Moisture content and screening. A fine, wet green-waste compost can exceed 800 kg/m3 while a dry, woody one may be under 400.