"Two tablespoons per 6 ounces of water" is terrible advice. Tablespoons measure volume, and coffee volume varies wildly depending on grind size and bean density. A tablespoon of finely ground dark roast weighs about 10 grams. A tablespoon of coarsely ground light roast weighs about 5 grams. Same scoop, completely different coffee.
Use a scale. A $12 kitchen scale is the single best coffee upgrade you can make. Weigh beans in grams, measure water in grams (1 mL = 1 gram). Done.
The Ratios by Method
Pour Over (V60, Chemex, Kalita Wave): 1:15 to 1:17. Start with 15g coffee to 250g water (1:16.7). This produces a clean, balanced cup. Want it stronger? Go 1:15. More delicate? Go 1:17. Most specialty coffee shops use somewhere in this range.
French Press: 1:15 to 1:16. French press needs a slightly stronger ratio because the metal mesh filter lets oils and fine particles through (which adds body but also dilutes perceived strength). 17g coffee to 270g water works well for a single mug.
Drip Machine: 1:16 to 1:17. Most drip machines are calibrated for a slightly weaker ratio. 60g of coffee per liter of water (about 1:16.7) is the SCA Gold Cup standard. If your drip coffee tastes watery, you're probably using too little coffee, not too much water.
Espresso: 1:2 by weight. This is a completely different ratio because espresso concentrates the coffee. 18g of ground coffee in, 36g of liquid espresso out, in about 25-30 seconds. This is the modern standard for a double shot.
Cold Brew: 1:5 to 1:8 (this makes concentrate). 100g of coarse-ground coffee to 500-800g of cold water, steeped 12-24 hours. Dilute the concentrate 1:1 with water or milk when serving. If you're drinking it straight at 1:5, it'll be intense.
AeroPress: 1:12 to 1:16 depending on your recipe. The AeroPress is flexible. 15g coffee to 200g water for a standard cup. 17g to 100g water for a concentrated shot you can dilute.
Why the Ratio Matters More Than the Beans
You can buy $25/bag single origin beans and ruin them with a 1:20 ratio (watery, thin, sour). You can take $12 grocery store beans and make them taste solid at 1:16 with the right grind and water temperature.
The ratio controls extraction. Too little coffee (high ratio like 1:20) means each particle is over-extracted - the water pulls out bitter compounds after the good stuff is already gone. Too much coffee (low ratio like 1:10) means under-extraction - sour and thin because the water couldn't pull enough flavor from the dense bed.
The Adjustment Framework
Coffee tastes bitter or harsh: use less coffee (go from 1:15 to 1:17) or grind coarser.
Coffee tastes sour or thin: use more coffee (go from 1:17 to 1:15) or grind finer.
Coffee tastes perfect but too strong: keep the ratio, add hot water after brewing (this is an Americano with pour over and it's totally valid).
Coffee tastes perfect but too weak: keep the ratio, use more of everything. 18g to 300g instead of 15g to 250g. Same ratio, bigger cup.