Coffee ratio calculator
How much coffee for how much water, at the published standard rather than the rounded version of it — because 55 g per litre and “1:18” are not the same ratio. Nothing you type here leaves your browser — it is worked out on your own device, so there is nothing to send and nothing to log.
The standard is 55 g per litre, not 1:18
The Specialty Coffee Association’s Golden Cup standard is 55 grams of coffee per litre of water, with a tolerance of ±10%.
Almost everywhere you see it, it has been converted to “1:18”. It is not 1:18. 55 g/L is 1:18.18, and a flat 1:18 works out at 55.56 g/L — about 1% stronger than the standard it is being quoted as.
One per cent will not ruin anybody’s coffee. It is here because a number quoted as a standard ought to be the standard, and because the same rounding turns the ±10% tolerance (49.5–60.5 g/L) into the much tidier and slightly wrong “50 to 60”.
Which way round is the ratio?
1:18 means one part coffee to eighteen parts water, by weight. A larger second number is weaker coffee, which is the opposite of how a strength setting usually reads and is the commonest way people get it backwards.
So the weak end of the SCA tolerance is 1:20.2 and the strong end is 1:16.5. If that feels inverted, it is because grams-per-litre and ratios run in opposite directions.
What this does not decide
The Golden Cup standard is a target for brewed strength — 1.15–1.35% dissolved solids at 18–22% extraction — arrived at through consumer panels for filter coffee. It is not a claim about what you should like, and the SCA’s own more recent work acknowledges that preference varies.
It is also for filter brewing. Espresso ratios are a different scale entirely, usually quoted between 1:1.5 and 1:3, and nothing on this page applies to them.