Check Your Compost Mix: Browns to Greens Ratio Calculator

This tool was built by Serge (MSc) using established science and government sources. My academic background covers plant biology, environmental biology, and biogeochemistry. My tools are for educational purposes and give practical guidance, not professional advice.

A compost pile that will not heat up, or that smells of ammonia, almost always has the wrong balance of browns and greens.

This calculator checks your mix against the balance that compost microbes work best at, and tells you what to add to fix it.

It uses the simple parts-by-volume method, which is the practical way to hit the ideal carbon-to-nitrogen balance without weighing anything.

Parts of greens you have

Greens are nitrogen-rich: kitchen scraps, grass clippings, coffee grounds, fresh plant cuttings.

Parts of browns you have

Browns are carbon-rich: dry leaves, cardboard, straw, wood chips, shredded paper.

Please enter the parts of greens and browns, above zero.

Your current mix:

Advice:

Aim for roughly 2 to 3 parts browns to 1 part greens by volume. When in doubt, add more browns.

How this works

Compost microbes work best at a carbon-to-nitrogen balance of around 25 to 30 parts carbon to 1 part nitrogen.

You cannot count atoms at home, so the practical stand-in is roughly 2 to 3 parts carbon-rich browns to 1 part nitrogen-rich greens by volume.

The calculator compares your parts of browns and greens to that target and tells you which way to adjust.

Understanding your result

If you have too few browns, the pile gets wet, dense, and smelly, since the extra nitrogen escapes as ammonia.

If you have too many browns, the pile just sits there and breaks down slowly.

Landing in the 2 to 3 parts browns to 1 part greens zone gives the microbes what they need to heat up and work fast.

Keep the pile damp like a wrung-out sponge and turn it now and then for air.

Important limitations

This uses parts by volume, which is a rule of thumb, not a lab measurement.

Different materials carry very different amounts of carbon and nitrogen, so a pile of woody browns behaves differently from one of shredded paper.

Treat the result as a starting balance and adjust by how the pile looks and smells over the following weeks.

Scientific basis

The carbon-to-nitrogen target behind this tool comes from Cornell University's composting program, part of the land-grant university system:

Keep Planning With These Calculators

I recommend these calculators alongside this one because finished compost ends up in beds, on top of soil, and in the pH and nutrient picture of the whole garden.

To plan how much compost and soil a bed can take, the Soil Volume Calculator converts bed size into litres, cubic feet, and bags.

Compost used as a surface layer pairs with the Mulch Calculator, which sizes the covering at the right depth.

If a soil test points to a pH problem, the Soil pH Amendment Calculator estimates the lime or sulphur needed alongside the compost.

Compost ratio (browns to greens)