Roast loss is the weight a batch loses in the roaster, as a share of the green weight that went in: (green in − roasted out) ÷ green in. A 12 kg batch that comes out at 10.2 kg lost 15%. To get the cost of a bag, divide the green price per kilogram by what's left after the loss (1 − loss), multiply by the coffee in the bag, then add the bag, the valve, the label, your time and a share of overhead. For the lot below, that's $2.45 of coffee in a 12 oz bag and $4.22 all in.
The short version
- Roast loss = (green in − roasted out) ÷ green in. Weigh every batch both ways.
- Roasted cost per kg = landed green cost per kg ÷ (1 − roast loss).
- Coffee in a bag = roasted cost per kg × kg in the bag (0.34 kg for 12 oz).
- Then add packaging, labor, gas and overhead, and allow for the coffee that goes to samples and cupping.
- Use each lot's own loss, not the house average. TaroStack records it on every roast; more below.
Step 1: roast loss
From a two-person roastery's log, batch R-0914-1 of the Brazil lot G-0907-BR:
Roast loss = (green in − roasted out) ÷ green in
= (12.0 − 10.2) ÷ 12.0
= 15.0%
In a spreadsheet, with green in D2 and roasted out in E2, it's =1-E2/D2, formatted as a percentage. That lot's
four batches that day lost 15.0%, 15.8%, 15.0% and 14.2%, and across all its batches it averaged 15.3%, which is the
number to cost with. The roastery's other lots lost between 12.5% and 17.1%, which is why one house average misprices
some of them. The whole log is in the coffee roaster inventory spreadsheet.
Step 2: what a kilogram of roasted coffee costs
Start from the landed cost of the green: what you paid per kilogram, plus freight and anything else it cost to get it to your door. The Brazil came to $6.10 a kilogram landed.
Roasted cost per kg = green cost per kg ÷ (1 − roast loss)
= $6.10 ÷ (1 − 0.153)
= $6.10 ÷ 0.847
= $7.20
It's a division, not a multiplication. Adding 15.3% to $6.10 gives $7.03, which is wrong: you need 1.18 kg of green to make a kilogram of roasted, so every roasted kilogram carries the cost of 1.18 kg of green.
Step 3: the coffee in one bag
A 12 oz bag holds 340 g, so 0.34 kg:
Coffee in a 12 oz bag = 0.34 × $7.20 = $2.45
Allow for the coffee that never reaches a bag: cupping, samples for cafés, the scoop that hits the floor. If that's about 1% of what you roast, divide by 0.99: $2.45 becomes $2.47.
Step 4: the full cost of a bag
| Per 12 oz bag | |
|---|---|
| Coffee ($7.20 × 0.34, with 1% for samples) | $2.47 |
| Bag with valve, and label | $0.48 |
| Labor (4 hours at $20 to roast and pack 120 bags) | $0.67 |
| Gas and roaster upkeep | $0.20 |
| Overhead (rent, insurance, the website, spread over the month's bags) | $0.40 |
| Full cost | $4.22 |
The labor line is the easiest one to leave out. Four 12 kg batches of the Brazil make about 40.8 kg of roasted coffee, which is 120 bags, and roasting plus packing them takes one person about four hours. The overhead and gas figures are examples; yours come from your own monthly bills divided by your monthly bags.
At a wholesale price of $9.00 a bag, that leaves $4.78, or 53%. Whether that's enough depends on what the café negotiates and what your retail price is, and the general method for getting from cost to price is in how to price baked goods, which works the same way for coffee.
What each point of loss costs
Roast the same Brazil darker and it loses more:
| Roast loss | Roasted cost per kg | Coffee in a 12 oz bag | Difference per bag |
|---|---|---|---|
| 15.3% | $7.20 | $2.45 | |
| 16.3% | $7.29 | $2.48 | +3¢ |
| 18.0% | $7.44 | $2.53 | +8¢ |
Eight cents a bag doesn't sound like much. On 300 bags a month it's $24, every month, on one lot, and it lands on the dark roasts, which lose the most. That's the case for costing each lot from its own loss, made with real money in coffee roaster inventory software, where the Colombian costs $3.93 a bag at its own loss and $3.83 at the house average.
A roast loss calculator, in six cells
If you'd rather not build the whole spreadsheet, this does the job:
A2 Green in (kg) 12.0
B2 Roasted out (kg) 10.2
C2 Green cost per kg 6.10
D2 Roast loss =1-B2/A2
E2 Roasted cost per kg =C2/(1-D2)
F2 Coffee in a 12 oz bag =E2*0.34
Change the bag weight in the last formula for 5 lb bags (2.268 kg) or 2 oz samples (0.057 kg).
Where this stops working
Every number depends on the roast log being filled in: weight in, weight out, which lot, every batch. That's easy when one person roasts and keeps a notebook by the roaster. It slips when two people roast on different days, when a batch gets roasted from two lots, or when the scale reading is written on the back of a hand and copied later. And the landed cost of green has to be updated every time a new lot arrives at a new price, or every bag is costed at last season's coffee.
How TaroStack does it
In TaroStack a roast is a batch with a yield, so the loss is recorded as you roast rather than worked out later. The green comes in as a lot, with freight and other landed costs spread over what arrived, so $6.10 a kilogram is what the lot really cost. When you record the roast, TaroStack takes 12 kg from the green lot you used, you enter the 10.2 kg that came out, and the batch shows its loss and its actual cost against the recipe's standard. The roasted cost is worked out on that batch, for that lot ($7.18 a kilogram for R-0914-1, at 15.0%), without anyone doing the division.
Packing is a second recipe: the bag, the valve and the label come off as stock, and the 12 oz bag gets its own lot from the roast, so the cost per bag follows the coffee that's actually in it. From your own batch history, TaroStack checks whether a roast yields what its recipe claims, which is how a drifting scale or a wetter lot shows up. One limit, plainly: labor isn't turned into dollars yet, so the labor line above is still yours to add.
Roasts, packing and true cost are on Standard at $99 a month, and the first 30 days are free. Your green lots and products import from a spreadsheet. If you'd like a hand setting up, ask, and we'll do it with you.