Compost Builder

×

Overview

The Compost Builder helps you design a fungal-dominated compost heap using locally available waste streams. Enter the feedstocks you have access to, set a C:N ratio target, and the calculator will work out the volumes you need.

1. Choose a Compost Target

Select one of the four target cards at the top. Each card represents a different C:N ratio range suited to a specific composting goal:

• Bacterial (15–20 : 1) — annual crops, vegetables, fast nutrient cycling
• Balanced (20–25 : 1) — general-purpose, mixed farming systems
• Fungal (25–30 : 1) — orchards, perennials, woody perennial systems
• Highly Fungal (30–40 : 1) — forest floor simulation, heavy wood-chip composting

The selected target sets the C:N range the calculator aims for. The gauge and status indicator update in real time as you add materials.

2. Set Heap Dimensions

Enter the length, width, and height of your planned compost heap in metres. The calculator shows the total heap volume automatically.

3. Add Feedstocks by Priority

Feedstocks are entered one at a time in order of priority — cheapest or most readily available first.

1. Select a material from the dropdown (or choose “Add new material…” to enter a custom feedstock with its own C:N ratio)
2. Enter the volume available in cubic metres
3. Click Add
4. The material appears in the priority list with a priority number. A new dropdown row opens for the next feedstock
5. Repeat until all your available feedstocks are entered

Materials already in the list are removed from the dropdown so you cannot add duplicates. Use the × button to remove a feedstock from the list.

4. Auto-Calculate

Press Auto-Calculate to let the tool work out the optimal volumes. The algorithm follows your priority order:

1. It uses all of the highest-priority feedstock first
2. Then adds as much of the next priority as needed
3. It continues down the list until the C:N ratio falls within your target range
4. When a partial volume of a feedstock brings the ratio into range, it calculates the exact amount needed

If the Heap Cap is on, the total will not exceed your heap volume. The algorithm may swap volumes between feedstocks to fit within the cap while still hitting the target ratio.

5. The C:N Gauge

The gauge shows your current C:N ratio in real time. The coloured zone represents your selected target range:

• Green zone — your mix is within the target range
• Left of green — too nitrogen-heavy (add more carbon materials)
• Right of green — too carbon-heavy (add more nitrogen materials)

The status text below the gauge tells you whether you are on target, and suggests which direction to adjust.

6. Editing Results

After auto-calculating, the Use Volume column in the results table is editable. Click any value to adjust it manually. The C:N ratio, gauge, and amendments update live as you type.

7. Amendments

The amendments section shows recommended additions based on your heap volume:

• Rock Phosphate — 2% of heap volume
• Agricultural Lime — 1% of heap volume
• Liquid IMO3 (LIMO) — 15 L per m³ of heap

These values adjust automatically when you change the heap dimensions or toggle the heap cap.

Tips

• Enter feedstocks in order from cheapest (free waste streams) to most expensive — the auto-calculator maximises use of your cheapest materials
• Use the heap cap when you have a fixed windrow size and want to fill it optimally
• Turn the heap cap off when you want to find out how much material you need regardless of heap size
• Custom feedstocks require a C:N ratio — if you do not know it, check a reference table or laboratory analysis
• Press Reset All to clear everything and start a new calculation