THE SHORT ANSWER
For everyday filter coffee, 1:16 is a practical starting point: one gram of dry coffee for every 16 g of brewing water. A 20 g dose therefore pairs with 320 g water. Treat the ratio as a starting recipe, not a rule for every brewing method.
The arithmetic, without the headache
Multiply your coffee dose by the second number. At 1:16, 15 g coffee needs 240 g water; 30 g needs 480 g. To work backwards, divide the water by 16. Weighing avoids the changing size of scoops and the gaps between beans in a spoon.
Strength and extraction are different
Ratio helps determine how concentrated the drink feels. Extraction describes what the water dissolves from the grounds. A strong cup can still taste poorly balanced. Before adding more coffee to every problem, ask whether you need a grind adjustment, a cleaner brewer or a different roast.
Build a house recipe
Choose a mug, write down one dose and keep it for three mornings. If the cup feels heavy, try a little more water. If it is too light, try a little less. Espresso and cold-brew concentrates need their own ratios, and espresso ratios normally compare dry coffee with finished beverage rather than all water entering the machine.
Change one thing, taste, and keep a short note. A recipe becomes useful when you can repeat the cup you enjoy.
Try it for yourself
Sources & further reading
Source links support the factual context. Our home recipes and tasting suggestions are identified as starting points.