A tablespoon of coffee varies by 4-8g depending on grind size and roast — the same "two scoops" can span nearly a 2x difference in actual coffee weight.
Coffee-to-water ratios (1:16 for pour-over, 1:15 for French press, 1:2 for espresso) are defined by weight because volume measurement is genuinely unreliable — a kitchen scale removes the single biggest source of inconsistent home coffee.
Weight fixes the dose, not the extraction. The same 18 g will taste sour or bitter depending on grind, water temperature and contact time — the scale removes one variable of several, and it is not the one that most often makes a bad cup.
Estimate with the rule, then check it against the calculator that models it properly.
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