Coffee Roast Weight Loss Calculator
Predict roasted coffee weight from green weight and roast loss, or find the loss percentage that describes your roast level.
How it works
Roasted weight = green weight × (1 − loss%) · Weight lost = green − roasted
Roasting drives off moisture and burns off some organic matter, so beans always weigh less after roasting than as green coffee — this "roast loss" or "shrinkage" typically runs 12–20%. The loss climbs with darker roasts because more water and mass are driven off, which makes measured loss a handy proxy for roast development. Knowing the loss lets you buy the right amount of green coffee to end up with the roasted weight you actually need.
Worked example
Roasting 1,000 g of green beans at a 15% loss leaves 1,000 × (1 − 0.15) = 850 g of roasted coffee, having shed 150 g of moisture and chaff — a medium roast.
Frequently asked questions
How much weight does coffee lose when roasted?
Usually 12–20%. Light roasts lose around 12–14%, mediums about 15%, and dark roasts 18% or more as additional water and organic material are driven off.
How do I buy enough green coffee?
Divide the roasted weight you want by (1 − loss). For 850 g roasted at 15% loss you need 850 ÷ 0.85 = 1,000 g of green beans.
Why does loss indicate roast level?
The longer and hotter you roast, the more moisture and mass are lost, so higher weight loss generally corresponds to a darker roast. It is one of several development metrics roasters track alongside time and colour.
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This calculator is for educational purposes. Double-check important results before acting on them.