Coffee Footprint Calculator
About 140 litres of water sit behind a single cup, almost all of it in growing the bean.
The formula
coffee = water / ratio
Ratios, not spoons
Coffee is measured by ratio because beans differ in density by more than a third between a light and a dark roast, so a scoop is not a fixed quantity. The Specialty Coffee Association standard is 55 g per litre, which is 1:18.2 — rather weaker than most people brew at home.
Grind matters more than ratio
Extraction depends on how much surface the water meets and for how long. A French press steeping four minutes needs a coarse grind; espresso pushing through in 25 seconds needs a fine one. Getting the grind wrong cannot be fixed by adjusting the ratio — under-extracted coffee tastes sour and thin, over-extracted tastes bitter and hollow, and both are ground problems rather than dose problems.
Cold brew is a different drink
Brewing cold for twelve to eighteen hours extracts far less of the acids and bitter compounds, which is why it tastes smooth and sweet at a strength that would be undrinkable hot. Concentrate is usually made at 1:8 and diluted to taste; brewed ready-to-drink it sits nearer 1:15.
Recipes are starting points
Ovens run hot or cold by 20 degrees, flour absorbs water differently by season and brand, and the same joint of meat cooks at a different rate depending on its shape rather than its weight. Everything here is a planning figure that gets you close enough to start, and the thermometer, the scales and your own notes from last time are what finish the job.