Compost Moisture Blend Calculator

How to use this estimate

Moisture percentages are treated as wet-basis mass fractions: water mass divided by total wet mass. The model solves for added material mass, assuming the starting blend and addition are homogeneous and no water evaporates during mixing. It does not determine compost maturity, sanitation, or an agronomic target.

Method

Added mass = starting mass × (target moisture - current moisture) / (added-material moisture - target moisture). A nonnegative finite addition exists only when target lies between the two moisture percentages (or equals the start, requiring no addition).

Worked example

Blending 100 lb at 35% moisture with material measured at 80% reaches a chosen 55% moisture at an estimated 80 lb addition, for 180 lb total.

Assumptions and supported inputs

Use measured dimensions and the listed field ranges. Values outside those bounds, missing entries, non-finite numbers, and fractional counts where a whole number is required are rejected. Displayed results are rounded to two decimal places; internal calculations retain full precision. This is a planning estimate, not a substitute for an on-site layout, product instructions, or a qualified trade decision where applicable.

Related planning tools

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Northstar Calculators provides this arithmetic for scenario planning. Verify the assumptions and physical fit before buying or building.