The short answer
Start at 1:16: one gram of coffee for every sixteen grams (millilitres) of water. That is 15 g of coffee for an 8 oz cup (240 g of water), 20 g for a standard 320 ml mug and 30 g for two cups (480 g). Bloom with twice the coffee's weight in water, then pour to the total and aim to finish in about three minutes.
From there, taste and adjust. A tighter ratio like 1:15 gives a stronger, heavier cup. A looser 1:17 stretches the same coffee into something lighter, closer to tea. Almost all good pour over lives between 1:14 and 1:18.
Pour over ratio chart by cup size
Coffee in grams at 1:15, 1:16 and 1:17, for the amount of water you pour:
240 g of water (one 8 oz cup): 16 g, 15 g, 14 g.
320 g (a standard mug): 21 g, 20 g, 19 g.
360 g (a 12 oz mug): 24 g, 22.5 g, 21 g.
480 g (two 8 oz cups): 32 g, 30 g, 28 g.
720 g (three cups): 48 g, 45 g, 42 g.
1,000 g (one litre): 67 g, 62.5 g, 59 g.
The water figure is what you pour, not what ends up in the cup. Wet grounds hold back roughly twice their own weight, so 20 g of coffee and 320 g of water gives you about 280 g to drink. If your mug is full at 320 g, pour closer to 360 g and use 22.5 g of coffee.
Why ratios beat scoops
Beans vary hugely in density. A level scoop of a dense light roast can weigh several grams more than the same scoop of a dark roast, so 'two scoops' means something different every time you change bags. Brewing by weight removes the variable, which is why a $15 kitchen scale improves more cups than most $100 gadgets.
If you have no scale yet, a level tablespoon of ground coffee weighs somewhere around 5 to 7 g, depending on the roast and the grind. The old rule printed on many bags, two tablespoons for every 6 oz of water, therefore lands anywhere from about 1:13 to 1:18. That spread is the whole argument for weighing.
Ratios also scale without thinking. Brewing for two? 40 g of coffee, 640 g of water. Still 1:16. The recipe never changes, only the quantities.
Common ratios at a glance
1:14 is strong and syrupy, and can turn muddy with fine grinds.
1:15 gives a rich, full cup that suits darker roasts.
1:16 is the balanced default and works for almost everything.
1:17 has a lighter body and more clarity, flattering bright, fruity light roasts.
1:18 is delicate and tea-like, and unforgiving of stale beans. It is also close to the Specialty Coffee Association's Golden Cup standard of 55 g of coffee per litre of water, plus or minus 10 percent, which is why some brew guides call 1:18 the official ratio. Most home recipes run a little stronger than that.
Bloom, then pour
Wet all the grounds with about twice their weight in water, so 40 g for a 20 g dose, and wait 30 to 45 seconds. Fresh coffee releases gas as it wets, and pouring straight through that pushes water around the bed instead of through it.
Then pour the rest in two or three stages, keeping the water level steady rather than flooding the cone. For a single cup, aim for the bed to finish draining somewhere between 2:30 and 3:30. A litre batch takes longer.
Use the drain time to set the grind, not the ratio. Much faster than that and the cup tends to taste thin, so grind finer. Much slower and it turns bitter, so grind coarser.
Does the brewer change the ratio?
Not really. 1:16 works in every dripper we cover. What changes is how much you can brew at once and how fast the water drains, and the grind is what absorbs that.
The Chemex counts a cup as 5 oz, so a full 6-cup Classic is about 890 g of water and 55 g of coffee at 1:16. Most people brew half that. Its thick bonded filter drains slowly, so go coarser than you would on a V60 rather than loosening the ratio.
The V60 is the reference single-cup cone, and 15 g to 240 g is the usual starting recipe. Its one large hole means pour speed controls the flow, so it rewards a steady kettle.
The Kalita Wave 185 brews 16 to 26 oz, which is roughly 30 to 48 g of coffee at 1:16. The flat bed and three small holes make it more forgiving of an uneven pour.
The Hario Switch 03 holds 360 ml, so 22.5 g of coffee fills it at 1:16. With the valve closed it steeps like a French press, and the ratio behaves the same way.
When the ratio isn't the problem
Sour or thin? The grind is usually too coarse or the water too cool. Bitter and harsh? Too fine, or the brew ran too long. The ratio is rarely the culprit in either case.
Fix one variable at a time. Lock the ratio at 1:16, dial the grind until the cup balances, and only then play with the ratio to taste. A consistent burr grinder makes the dialling-in far easier than any blade grinder will.
Water temperature matters too. Aim for 90 to 96°C, which in practice means just off the boil. Cooler water under-extracts light roasts. Very hot water can push dark roasts into bitterness. No thermometer? Thirty seconds off the boil lands you in the zone.