Enrichment · Cultural Studies · Gardening

How much compost
to order, before
the truck arrives.

List your beds and choose a depth. The calculator gives the cubic yards and the bags, then sets bag prices against a bulk load with delivery, so you buy once and buy enough.

Work out the amountWhat you get

The soil amendment calculator

The worked example is made up: 2 inches of compost on three raised beds and an herb strip. Nothing you type leaves this browser.

Loading the calculator. If nothing appears, turn on JavaScript.

What you get

Enrichment · Cultural StudiesFree

What you finish with
Area, cubic feet and cubic yards, each bed’s volume, the number of bags and their cost, and the bulk cost with delivery. It prints as a summary and downloads as a spreadsheet.
Who it is for
Home and school gardeners, families building raised beds, and students practising area and volume.
Format
Browser calculator for a phone, tablet or computer, by touch or keyboard. Prints a summary; downloads a spreadsheet (.csv); export and import a file.
Access
Free. No account, no sign-in and nothing to install. Everything you type stays in this browser; nothing is sent to Caveat.
Where it lives
The Cultural Studies space in Caveat Enrichment.
Support
Questions, a correction or a request: team@caveatacademic.com.

How to use it

  1. Add each bed size and how many there are.
  2. Type the depth and choose a settling allowance.
  3. Choose the bag size and type bag and bulk prices.
  4. Read cubic yards, bags and which is cheaper.
  5. Print the summary for the garden centre.

Work out the amount

How the amounts are worked out

Area, depth, and a unit that trips everyone up.

The worked example: compost for four bedsArea121 sq ft3 × 8 × 4 + 10 × 2.5× depth20.2 cu ft× 2 in ÷ 12+ settling22.2 cu ft+ 10%÷ 270.82 cu ydor 15 bags of 1.5 cu ftThe worked example: compost for four bedsArea121 sq ft3 × 8 × 4 + 10 × 2.5× depth20.2 cu ft× 2 in ÷ 12+ settling22.2 cu ft+ 10%÷ 270.82 cu ydor 15 bags of 1.5 cu ft
Area times depth gives volume; the depth is in inches, so divide by 12 to stay in feet, and by 27 to buy by the yard.

The arithmetic

Volume is area times depth, but beds are measured in feet and depth in inches, so the depth is divided by 12. Bulk material is sold by the cubic yard, a cube 3 feet on a side, which holds 27 cubic feet, not 9. Loose compost and mulch settle as they are watered, so add about 10 percent; very fluffy mixes can settle more.

How deep to spread

University extension services generally suggest working 1 to 3 inches of compost into the top 6 to 8 inches of a garden bed, and 2 to 3 inches of mulch on the surface, kept back from stems and trunks. Filling a new raised bed is a different job: there the depth is the full bed height, and the mix sinks over the first season.

Sources

  1. Colorado State University Extension. Fact sheet 7.235, Choosing a soil amendment (extension.colostate.edu).
  2. Penn State Extension. Mulching landscape plants (extension.psu.edu).
  3. University of Minnesota Extension. Building raised beds and improving garden soil (extension.umn.edu).
  4. National Institute of Standards and Technology. Handbook 44, appendix C: units of volume, 27 cubic feet to the cubic yard (nist.gov).

The worked example is made up. Prices are what you type; check bag volumes on the label. Your figures stay in this browser. Support: team@caveatacademic.com.