Coffee ratio calculator
Coffee grounds retain roughly two grams of water for every gram of coffee. Brew 500 g of water with 30 g of coffee and about 60 g stays in the filter, so you pour around 440 ml rather than 500. For a single cup it is a rounding error; for a carafe you meant to fill exactly, it is why it comes up short.
Brew ratios are stated by weight: 1:16 means one gram of coffee to sixteen of water. Five hundred grams of water at 1:16 needs 31 g of coffee. Stronger sits around 1:15, lighter around 1:17.
How to use a brew ratio
Ratio sets strength, but grind size sets extraction, and confusing the two is why adjustments often fail. A brew that tastes thin and sour is under-extracted and needs a finer grind or a longer time, not more coffee. One that tastes harsh and bitter is over-extracted and needs a coarser grind. Adding coffee to a sour brew makes a stronger sour brew. Change one variable at a time, and change the grind before the ratio.
Questions
1:16 by weight is the common starting point. 1:15 is stronger, 1:17 lighter.