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Grinder Purge Calculator
Your grinder keeps a little of yesterday's coffee inside it. So you purge — a quick grind-and-dump in the morning and after every grind change. That is the right habit, but it is not free. Enter how much you purge and how often, and this calculator shows the real cost: grams a day, whole shots a month, and dollars a year in the bin.
1Your grinder and your purging habit
Presets set the purge slider — drag it if you have weighed your own retention (grind, weigh what comes out vs what went in; the gap is retention).
How many grams you grind and throw away each time you purge — roughly your grinder's retention, cleared once.
Count the morning clear-out plus one for every grind-size change you dial in that day. One morning purge only = 1.
Used to turn wasted grams into wasted shots — the number that actually stings.
2What the bin is eating
Share of a bag wasted each month: about 35% of a 340 g bag
?Three ways to purge less without stale shots
☀️ One morning purge beats five small ones
Stale grounds do their damage overnight, not between shots an hour apart. Clear the grinder once when you start, then leave it alone unless you change the grind size by a lot.
🔔 A bellows or a puff clears most of it
On many single-dose grinders a bellows puff after grinding pushes retained grounds out into the cup instead of the bin. What lands in the dose is not waste at all.
⚖️ Single-dose if the number above hurts
Weighing beans per shot and running the grinder empty each time cuts retention to a fraction of a gram. Run this calculator at 0.3 g to see the yearly difference before you buy anything.
?Grinder Purge FAQ
Do I actually need to purge at all?
If your grinder holds grounds overnight, yes — a small one. Retained grounds go stale and the first shot of the day pulls a mix of old and new coffee. One purge about equal to the retention amount clears it. Skipping it entirely saves the grams above and costs you the first shot's taste instead.
How do I weigh my grinder's retention?
Clean the grinder out as well as you can, weigh 18 g of beans in, grind it all through, and weigh what lands in the cup. The missing grams are sitting inside. Repeat once — retention on an empty grinder is higher than on one already in use, so the second run is the honest everyday number.
Is purging after every grind change wasteful?
A change needs a purge — the first grounds out are still at the old setting. But a one-notch nudge mixes in within a gram or two; a big swing needs the full retention amount. Match the purge to the size of the change instead of running a full dose through every time.
Can I use purge grounds for anything?
They are stale for espresso but fine for a French press top-up, cold brew experiments, or the compost. Most people who track the number in this calculator just bin them — the point is knowing what the habit costs, not rescuing every gram.
Are these costs exact?
The grams are your inputs; the money math is exact on a 30-day month: waste per day × 30, priced at your bag price ÷ bag size. If you brew five days a week instead of seven, scale the monthly figures by about 0.7 — the habit ranking stays the same.