How to calculate roast loss: a practical guide for coffee roasters

If you sell a 12 oz bag of roasted coffee, you did not pull 12 oz of green from inventory. You pulled closer to 14.5 oz — more if you roast dark, less if you roast light. That gap is roast loss, and it is the single most common reason roasters think their green inventory is accurate when it is quietly lying to them.

What roast loss actually is

Roast loss is the weight your green coffee gives up during roasting — mostly water in the early phase, then organic matter (chaff, CO2, volatile aromatics) as development progresses. The percentage is almost entirely driven by development time and end temperature, which is why the same lot roasted to a light and a dark profile can differ by 5+ percentage points in final yield.

The math, in one line

green ounces required = roasted ounces sold ÷ (1 − loss%). A 12 oz bag at 16% loss needs 12 ÷ 0.84 ≈ 14.29 oz of green. A 12 oz bag at 20% loss needs 15 oz. Multiply that by a few hundred bags a month and the delta between 'close enough' and 'correct' becomes inventory you didn't know you had — or didn't know you lost.

Measuring loss per profile

1. Weigh green before charging (to the gram, not the pound).
2. Roast normally and note the profile used.
3. Weigh roasted output after it has cooled (same day).
4. Loss % = (green − roasted) ÷ green × 100.
5. Repeat 3–5 times per profile and take the average. One batch is not data.

Once you have a stable per-profile loss number, stop guessing. Every product you sell maps to a roast profile. Every order should back-calculate to green on its own, without you touching a spreadsheet.