Coffee-to-Water Ratio Explained: How to Calculate It
People ask me for the "right" coffee-to-water ratio like there's one magic number. There isn't — but the ratio is just the weight of grounds compared to water, written as 1:15 or 1:16, meaning 1 gram of coffee for every 15 or 16 grams (or ml) of water. Here's how I think about it.
The formula
Water (g) = Coffee (g) × Ratio. Or Coffee (g) = Water (g) ÷ Ratio. Because both are weighed, the result stays accurate whether you brew 200 ml or 2 litres.
Worked example
For 300 g of water at a 1:16 ratio: 300 ÷ 16 = 18.75 g of coffee. The OneCup Recipe Calculator does this for you and scales to any amount.
What the number means
- Lower ratio (1:13–1:15) → stronger, bolder cup.
- Higher ratio (1:16–1:18) → lighter, more diluted cup.
Ratio is a starting point, not a rule. Beans, grind, and taste shift the best value. See my Methodology for how I label sources.
Where the number comes from
I'm not pulling 1:16 out of thin air. Ratio guidance is everywhere — the SCA's brewing reference lands around 55 g/L, roughly 1:18, for filter coffee. I treat that as one public reference, not a rule for every bean and method. Find the number that tastes right to you.