What is the ideal green to brown ratio?

By volume, aim for roughly 1 part green to 2-3 parts brown. By weight, the optimal carbon-to-nitrogen ratio is 25-30:1. Volume ratio is easier to judge in practice.

What counts as green material?

Greens are nitrogen-rich: grass clippings, fruit/veg peelings, coffee grounds, fresh plant trimmings, and weeds (without seeds).

What counts as brown material?

Browns are carbon-rich: dry leaves, cardboard, newspaper, straw, wood chips, sawdust, and dry garden stalks.

My compost is slimy and smells, what should I do?

Add more brown materials and turn the heap. Slimy, smelly compost has too much nitrogen (green) and not enough carbon (brown) and airflow.

Can I compost cooked food?

Avoid cooked food, meat, and dairy in open compost heaps as they attract rats. These can go in a sealed hot composter or Bokashi bin, then be added to compost.

GardenCalcs.uk

Green to Brown Ratio Calculator — Compost Balance

Balance green and brown materials for optimal composting.

Green Materials — nitrogen-rich (litres per week)

Grass Clippings

Fresh mowings, high in nitrogen. Add thin layers — a full grass box is roughly 30-40 L and mats down if piled deep.

Kitchen Scraps

Fruit/veg peelings, coffee grounds, tea, crushed eggshells (a full kitchen caddy is about 5 L). No cooked food, meat or dairy.

Fresh Leaves/Weeds

Green plant trimmings and annual weeds — leave out anything in seed or with running roots like bindweed.

Brown Materials — carbon-rich (litres per week)

Dry Leaves

Autumn leaves once brown and crisp — a key free carbon source. Scrunch handfuls to stop them packing flat.

Cardboard/Paper

Torn corrugated cardboard, egg boxes, newspaper — scrunch or shred. Remove tape and glossy print.

Woody Prunings

Shredded twigs and chipped wood. Slow to break down, so chop small and add sparingly to keep the heap aerated.

Straw

Straw or dried stalks add bulk and air gaps. Loosen compacted flakes before adding so the centre stays oxygenated.

How We Calculate This

This calculator totals your green (nitrogen-rich) and brown (carbon-rich) materials by volume, then checks the ratio against composting best practice.

The ideal ratio by volume is 1 part green to 2-3 parts brown. This typically produces the 25-30:1 carbon-to-nitrogen ratio that microbes need for efficient decomposition.

Too much green = wet, slimy, anaerobic compost. Too much brown = dry, slow decomposition.

Frequently Asked Questions

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Last updated: February 2026

All calculations are estimates based on standard gardening guidelines. Results may vary with soil conditions, climate, and plant varieties.