The brew-ratio formula
Coffee strength is set by the ratio of coffee to water by weight. Because 1 ml of water weighs 1 gram, cup volume converts directly to water weight:
water (g) = cups × cup size (ml)
coffee (g) = water (g) ÷ ratio
A ratio of 1:16 means one gram of coffee for every 16 grams of water. Lowering the ratio number (toward 1:14) makes a stronger brew; raising it (toward 1:18) makes it milder.
Worked example
Two 240 ml cups at a 1:16 ratio:
Water: 2 × 240 = 480 g.
Coffee: 480 ÷ 16 = 30 g.
Brew: 30 g coffee + 480 g water.
Golden ratio: the Specialty Coffee Association's classic guideline is around 1:16–1:18 by weight. Dial within that band to taste — go stronger for darker roasts, lighter for delicate ones.
Ratios by brew method
Pour-over and drip sit comfortably near 1:16. French press is often brewed a touch stronger at about 1:15. Cold brew and concentrates use much stronger ratios such as 1:8, then dilute before serving. The strength toggle gives you a fast 1:15 / 1:16 / 1:18 starting point.