Ten pounds of green went in. Eight and a half came out.
Type in your green weight, your loss, and your bag size — get the roasted weight, the bags you can actually sell with the leftover called out, and the true green cost riding in each one. Everything stays in your browser.
The roast
The standing order
The numbers here are yours to check. This page does arithmetic on what you type — it cannot see your recipe, your equipment or your batch.
For anything you will eat or sell as food, double-check it against your own process and your local rules. This page does maths, not food safety.
Want it to remember?
In MadeKeeper, logging a roast pulls the green beans out of inventory and cascades your roasted cost per pound straight into the cost of every 12-oz bag and the price on your market table. See for growers & farmstands or poke around the live demo. $19/mo for the whole back office, kept for as long as you stay. The shop stays free for cost a piece and one fair — no product cap. The tax packet, Etsy and Square, and more fairs are the $19.
Free tool · Small-batch coffee roasting
The math that trips up every garage roaster at least once, worked through with the same numbers the calculator runs — a 10 lb batch at 15% loss, packed into 12-oz bags.
Why did my ten pounds of green turn into eight and a half pounds of roasted?
Roasting drives off water, and the beans leave the drum lighter than they went in — plus a little chaff on the way. How much lighter is the most argued number in small-batch roasting: light roasts commonly land around 11–13% loss and dark roasts around 16–20%, which is why this calculator treats loss as a setting seeded at 15% — a stated middle — instead of pretending it's a constant. Weigh in and weigh out for a few batches, then use your own number; your log beats anyone's chart.
How much green coffee does a 12-oz bag actually take?
Divide the bag weight by one minus your loss — don't multiply. At 15% loss, a 12-oz bag needs 12 ÷ 0.85, about 14.1 oz of green; the tempting shortcut of 12 × 1.15 gives 13.8 oz and leaves every bag a little short. It's the same trap that makes a pound of green feel like a pound of roasted right up until the scale disagrees.
Why does the calculator round bags down and show a leftover?
Because 11.3 bags is 11 bags — the .3 isn't a sellable bag, it's the open jar by the grinder. From 10 lb of green at 15% loss you get 8.5 lb of roasted, 136 oz, which fills 11 twelve-oz bags with 4 oz left over; a calculator that says 12 is quietly lying to your price. And if you pack a few grams heavy so no customer ever opens a light bag, that giveaway is a setting too — enter your overfill per bag and the bag count honors it.
What did each bag really cost me in green?
Divide your whole green spend by the bags you can sell. Ten pounds at $6.50/lb is $65, and if that batch gave you 11 bags, each one carries $5.91 of green — not the $5.74 you'd get by pricing only the 14.1 oz that ended up inside it. The leftover ounces don't pay for themselves, so the sellable bags have to; that's where the cash actually went.