07 January 2019

Making coffee: unit conversions in everyday life

We replaced our coffee grinder and coffee maker. This fact wouldn't ordinarily be blog-worthy; we've generally found these everyday appliances to have a useful life of a few years, after which point they don't seem to work as well. This replacement round brought a small puzzle and lesson, though. Our prior grinder had a dial setting, numbered in "cups", corresponding to the intended number of cups of coffee which a grinding cycle was intended to serve. I put "cups" in quotes, because it was intended to align with a corresponding measure on the same manufacturer's coffeemaker. I'd taken to calling them Arbitrary Coffee Units, or ACUs. I think that those "cups" may have been 6 ounces each, though our new coffeemaker designates its "cups" as 5 ounces. Clearly, either of those is smaller than the 8 ounces in a standard, measuring, unquoted cup.

But, our new grinder doesn't have a numbered dial. Perhaps to embrace coffee purists, other minimalists, or perhaps to avoid the cost of a timer mechanism, it just has an on-off switch. You put as much whole-bean coffee into the hopper as you need, and grind until it's done and ground. You wouldn't want to grind more, as the excess would go stale quickly. But how much whole-bean coffee do you need to brew a pot? One recommendation urged a large number of tablespoons of ground coffee, which seemed messy and inconvenient and still wouldn't answer the question of how many beans to process in order to obtain that ground result. A friend suggested their practice of weighing 66 grams of coffee to fuel their 8-cup coffeemaker - and, no, I'm not sure how large its cups are - but we didn't have a suitably precise kitchen scale and didn't want to add something else to the counter. I converted weight to volume by weighing a measuring cup with and without coffee beans on a postal scale set to metric, and found that an (8-ounce) cup of the coffee beans that I tested weighed about 72 grams, not too far off. In our kitchen for the moment, therefore, we grind a loosely-filled measuring cup of beans to yield 8 of our current ACUs and are enjoying the result.


  1. Our super duper fancy coffee maker (approved by the Coffee Geeks of America, or some similar-sounding body) turns out to use 5 oz cups after all. The coffee math I was taught was 17-1 by weight for water-to-beans. That comes out to 70 grams for 1.2L (40 oz). We seem to prefer it a bit less strong at 66g.

    1. Actually, the organization is the SCAA - Specialty Coffee Association of America. The name sounds suspicious, as if it's responsible for mint-flavored coffees and similar offenses.