Compost Calculator

Compost turns up in two separate questions and this handles both. The first is how much to buy: enter the area and the depth and you get cubic feet, bulk yards, bags, weight and the rate per thousand square feet that soil reports are written in. The second is how to build a pile: enter what is going in it by weight and you get the resulting carbon-to-nitrogen ratio, whether that lands in the band a pile needs, and how much more of one material it takes to reach the target. The ratios in the picker are mid-range figures from composting tables rather than measurements, and the arithmetic assumes each material is a similar share of carbon by dry weight, which is the usual simplification.

Calculator Type

Units

Square feet, inches, cubic yards, pounds Square metres, centimetres, cubic metres, kilograms

The bag picker below covers both markets whichever you choose, because a bag is whatever size it is printed with.

A thin layer over a bed or a lawn: volume, bulk order, bags and weight, plus the spread rate soil reports are written in.

Area to Cover (sq ft) *

Square feet, or square metres in metric. Length times width for a rectangle. For a bed of an awkward shape, break it into rectangles and add them up.

Depth (in) *

A quarter to half an inch over a lawn, half to one inch over a bed each year, and up to two inches when starting a new bed. More than an inch at once on a lawn smothers the grass.

Bag Size

Price per Bag ($, optional)

Price per Bulk Unit Delivered ($, optional)

Per cubic yard, or per cubic metre in metric. Fill both prices in to see which way is cheaper.

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Weights In

Pounds Kilograms

All three weights are read in whichever you pick.

Enter what is going in the pile by weight. This gives the resulting C:N ratio and how much more of one material it takes to reach the target.

First Material

First Material C:N If You Chose "Something Else"

First Material Weight (lb) *

Second Material

Second Material C:N If You Chose "Something Else"

Second Material Weight (lb) *

Third Material (optional)

Third Material C:N If You Chose "Something Else"

Third Material Weight (lb)

Target C:N Ratio

A pile aims at 25 to 35 parts carbon to one of nitrogen. Thirty is the usual target.

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