Enter amounts as roughly equal-sized units (5-gallon buckets, wheelbarrow loads, whatever's consistent) — the ratio only cares about proportions, not the actual unit.
Reading Your Ratio
25:1 to 30:1 is the sweet spot for a hot, actively decomposing pile — that's the ratio soil microbes work fastest at, breaking material down in weeks to a few months instead of a year or more.
Too high (too much carbon) and the pile breaks down painfully slowly — microbes run out of nitrogen before they can process all that carbon, so straw and leaves just sit there. The fix is more greens: grass clippings, kitchen scraps, or a nitrogen source like manure.
Too low (too much nitrogen) and the pile turns anaerobic and starts to smell like ammonia, since there's more nitrogen than the microbes can use and it off-gasses instead. The fix is more browns: dry leaves, straw, or shredded cardboard.
This calculator uses a simplified weighted-average method based on the volume of material you add, which is the standard approach most home composting guides use. It gets you close enough to guide real decisions, though the true ratio also depends on moisture content and particle size, which this can't measure for you.