Tool · ratio

Coffee-to-water ratio: the guide and the calculator

The ratio — grams of water per gram of coffee — is the single most useful number in home brewing. Here is where the common targets come from, and a calculator that does the arithmetic.

Updated 2026-10-14 · sources listed at the end

One milliliter of water weighs about one gram, so you can read the water result as grams on a scale or milliliters in a measuring jug. The ratio is measured on the water you pour, not on the coffee that ends up in the cup — the grounds keep some of it.

The formula

Where the targets come from

The SCA "Golden Cup" reference: 55 g per liter

The Specialty Coffee Association's published best practices recommend a coffee-to-water ratio of 55 g/L ± 10%, with water at 200°F ± 5° (93.0°C ± 3°) at the point of contact. That is about 1:18.2, and the ±10% allowance covers roughly 1:16.5 to 1:20. The SCA's 2021 home-brewer standard (Standard 310-2021) uses the same 55 g of coffee per 1.000 kg of water as its test ratio and expects the finished brew to reach a strength of 1.15–1.55% total dissolved solids.

The brewing control chart

Those numbers trace back to Ernest Earl Lockhart, who, as director of the Coffee Brewing Institute, published work in 1957 proposing that coffee quality could be indexed by how much of the grounds dissolve. The resulting Coffee Brewing Control Chart plots strength (TDS) against extraction (percent of the grounds dissolved), with brew ratios drawn as diagonal lines and an "ideal" box in the middle. Commonly cited targets are an extraction of 18–22% and a strength of 1.15–1.35% under the American standard (European and Norwegian standards sit somewhat higher). To place your own brew on the chart, measure its TDS and use the extraction yield calculator.

Recent UC Davis Coffee Center research, run with the SCA's Coffee Science Foundation, revisited the chart with trained panels and more than 58,000 sensory data points. It found, for example, that bitterness rises with both strength and extraction, while sweetness was highest in the low-strength, low-extraction corner — evidence that "weak" and "strong" labels are too simple. A related model from the same program suggests that, for immersion brewing, strength is controlled more easily by changing the ratio than by chasing extraction.

Ratios by brew method

Note the espresso row: there the ratio is usually quoted as dry coffee to finished beverage, not water poured, so it is not directly comparable to the filter rows — the espresso ratio guide covers dose, yield and shot time, with a yield calculator. Cold brew is different again: it is often steeped as a strong concentrate and diluted afterwards — see the cold brew guide.

How to use the ratio in practice

1. Pick a starting point. For filter coffee, 1:16 is a central value inside both the SCA allowance and the common range.
2. Too strong or too weak? Change the ratio first. It moves strength predictably.
3. Sour, hollow or bitter at a ratio you like? That points to extraction — adjust grind size or contact time rather than the ratio.
4. Changed roast level? Roast affects how readily coffee extracts, so re-taste and re-dial the ratio when you switch from a medium to a dark roast.
5. Write it down. Dose, water, grind setting, time. Change one thing per brew.

Per cup: 55 g/L (the SCA/American reference) to 63 g/L (the Norwegian standard) works out to about 13–15 g of coffee per 240 ml of water (240 × 0.055 = 13.2 g; 240 × 0.063 = 15.1 g); some references round this up to 14–16 g. For every common cup size and ratio in one table, use the printable coffee ratio chart. A scale removes the guesswork — see coffee scales explained.