Coffee goes into the drum heavier than it comes out. Between eleven and twenty percent of the green weight leaves as water vapour and gas, and that lost weight quietly changes three numbers a business runs on: how much green coffee to buy, how much a roaster really produces, and what a kilogram of roasted coffee costs. This guide gives the figures, the arithmetic, and a table to work from.
What is lost, and how much
Green coffee arrives at around 10–12% moisture. Roasting drives nearly all of it out as steam, and the chemical reactions of roasting release carbon dioxide and other gases as well. Chaff — the silverskin that separates in the drum — leaves too. The total is the roast loss, and it rises with roast degree because more of the bean's structure is broken down the further the roast goes.
Typical figures for washed arabica:
| Roast degree | Weight loss | Roasted yield from 1 kg green |
|---|---|---|
| Very light, dropped at the start of first crack | 10–12% | 0.88–0.90 kg |
| Light to medium-light | 12–14% | 0.86–0.88 kg |
| Medium | 14–16% | 0.84–0.86 kg |
| Medium-dark | 16–18% | 0.82–0.84 kg |
| Dark, into second crack | 18–20% | 0.80–0.82 kg |
| Very dark | 20–25% | 0.75–0.80 kg |
Two cautions. Naturals and honeys with more chaff, and coffees that arrive wetter than 12%, lose a little more. And these are ranges, not your numbers — the last section explains why.
The three numbers it changes
1. How much green coffee to order
Work backward from roasted demand. If you sell 100 kg of roasted coffee a week at a medium roast losing 15%, the green required is 100 ÷ 0.85 ≈ 118 kg. For a dark roast at 20% it is 125 kg. Ordering 100 kg of green for 100 kg of sales leaves you 15–20% short — a mistake that appears in the second month, when the shelf is empty before the next shipment lands.
A quick rule: green needed = roasted needed ÷ (1 − loss). For planning, divide by 0.85 for medium and 0.80 for dark and you will be close.
Green coffee is also bought in bags of fixed size — commonly 60 or 70 kg — so round the requirement up to whole bags and add a margin for cupping, profile development and the occasional rejected batch. Storage conditions then keep that margin usable; see green coffee storage.
2. What the roaster actually produces
A roaster's capacity is rated in green weight charged. A 12 kg machine charged with 12 kg of green does not make 12 kg of coffee; at medium roast it makes about 10.2 kg. Over a day of eight batches that is nearly 82 kg of roasted output, not 96.
This matters when sizing a machine. A roastery that needs 400 kg of roasted coffee a week and reads the spec sheet as roasted output will buy a machine that is 15–20% too small and discover it on the first full week. Size from roasted demand, convert to green with the loss factor, then match the green figure to batch size and batches per day — the method in our batch size guide and, for the models, our commercial coffee roaster range.
3. What a roasted kilogram costs
Green coffee is priced per green kilogram. Roasted coffee is sold per roasted kilogram. The loss sits between them. If green costs a certain amount per kilogram and you lose 15%, the green cost per roasted kilogram is that figure ÷ 0.85 — about 18% higher. At 20% loss it is 25% higher. Any costing that uses the green price per kilogram as the cost of the coffee in the bag understates it by that margin, and the error compounds on every bag sold. Fuel, labour and packaging are then added on top; see coffee roaster running costs.
Measuring your own loss
The ranges above are a starting point. The number to use is the one your machine produces, and it is easy to get.
Weigh the green charge. Roast. Cool completely — not "cool enough to handle" but room temperature, because the beans keep losing a little weight as they finish degassing on the tray. Weigh the roasted batch. Then:
loss % = (green − roasted) ÷ green × 100
Do this for every batch in the first weeks on a new machine and record it against roast degree and coffee. You will find your machine has its own loss figure for each coffee at each drop point, and it will differ from published ranges by a point or two, because airflow, batch size and drum design all change how much moisture and chaff leave. A high-airflow roaster loses slightly more than a low-airflow one at the same colour. A roast log with loss recorded alongside the curve is also one of the best consistency checks available: if two batches of the same coffee dropped at the same temperature show different loss, they were not the same roast.
Using loss as a quality tool
Beyond planning, loss percentage is a check on the roast itself. Roasters who track it use it two ways.
As a roast-degree confirmation. Colour meters are expensive; a scale is not. Once you know that your medium roast of a given coffee loses 15.2%, a batch that loses 14.1% was dropped early and one that loses 16.5% went long — before anyone has tasted it.
As a moisture check on incoming green. A new lot of the same coffee that loses noticeably more at the same drop point arrived wetter, or has been sitting in a humid store. That is worth knowing before the profile is blamed. Roast faults and their signatures are in coffee roast defects.
A worked example
A roastery sells 250 kg of roasted coffee a week: 200 kg at medium (15% loss) and 50 kg at dark (20%).
- Green for the medium: 200 ÷ 0.85 = 235 kg
- Green for the dark: 50 ÷ 0.80 = 63 kg
- Total green: 298 kg per week, round to five 60 kg bags, plus margin
- Machine: a 15 kg roaster charged at 15 kg green yields about 12.7 kg medium per batch; 298 kg green is 20 batches a week — four batches a day over five days, comfortably inside one shift with a between-batch protocol
- Cost per roasted kg: green price ÷ 0.85 for the medium, ÷ 0.80 for the dark, before fuel, labour and packaging
Change the roast degree, and every line changes with it.
FAQ
How much weight does coffee lose when roasted?
Between about 11% and 20% for most commercial roasts — lighter roasts at the low end, darker at the high end, and very dark roasts up to 25%. Most of the loss is water; the rest is carbon dioxide, other gases and chaff. Measure your own machine's figure rather than relying on published ranges.
How much green coffee do I need for 1 kg of roasted coffee?
Divide 1 kg by (1 − loss). At a medium roast losing 15% you need about 1.18 kg of green; at a dark roast losing 20% about 1.25 kg. For weekly planning, divide roasted demand by 0.85 for medium and 0.80 for dark, then round up to whole bags.
Does a 12 kg roaster produce 12 kg of coffee?
No. Capacity is rated in green weight charged. A 12 kg charge at a medium roast yields about 10.2 kg of roasted coffee; at a dark roast about 9.6 kg. Size a machine from roasted demand converted to green, not from the roasted figure alone.
When should I weigh the roasted coffee?
After it has cooled fully to room temperature. Beans continue to release gas and lose a little weight for some minutes after leaving the drum, so weighing on a warm tray reads high and understates the loss. Weigh green before charging and roasted once cold, then calculate.
Why is my weight loss different from published figures?
Because loss depends on your machine's airflow, batch size and drum design as well as roast degree and the coffee's moisture and processing. A point or two either way is normal. Build your own table by recording loss for each coffee and drop point; that table is the one to plan from.
Can weight loss tell me if a roast is consistent?
Yes. For the same coffee dropped at the same point, loss should repeat within a few tenths of a percent. A batch that loses noticeably less was dropped early; one that loses more went long or the green was wetter. It is a cheap, fast check that needs only a scale.
Does weight loss affect the cost of roasted coffee?
Directly. Green is bought per green kilogram and sold per roasted kilogram, so the green cost per roasted kilogram is the green price divided by (1 − loss) — about 18% higher at 15% loss and 25% higher at 20%. Costing that ignores this understates every bag.
Final Thoughts
Roast loss decides how much green you buy, how much your roaster really makes and what each roasted kilogram costs. Measure it on your own machine, keep it on the log, and size everything from roasted demand converted to green. If you are choosing a machine, tell us your weekly roasted volume and roast degree and we will do the conversion with you — for any capacity in our commercial coffee roaster range, from the 3 kg up.
Request a factory-direct quote or message us on WhatsApp at +86 184 0771 4607.
Get a Quote → WhatsApp +86 184 0771 4607Last updated: September 17, 2026
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