Coffee ratios: why 1:16 doesn't give you 1:16 in the cup

Why you’d do this

You weigh 18 g of coffee, pour 288 g of water for a 1:16 brew, and expect 288 g in the cup. You get something closer to 250 g. Nothing is wrong with your pouring: dry coffee grounds soak up water and keep it, and that water never reaches the cup. A plain ratio widget ignores this, which is why a “1:16” recipe and a “1:16” result are two different numbers.

The Coffee Brew Calculator includes the missing step. It tells you the water to pour, the water the grounds keep, and what actually lands in the cup, so you can work from the cup size you want and get the dose right the first time.

How, with the named tool

1. Pick the method. Choose V60, Chemex, AeroPress, French press, Moka pot, Cold brew or Espresso. The ratio, grind, water temperature and time guidance change with it; your dose stays put.
2. Choose what to solve for. Under Solve for, pick I have beans to go from a dose to the cup, or I want a cup size to work backwards from the amount you want to drink.
3. Enter the amount and ratio. Type the grams in Coffee dose (or Desired yield in cup), or use the − and + buttons and the 1 cup, 2 cups and 4 cups chips. Set the ratio with the slider or the Strong, Balanced and Light presets.
4. Read the result. The tiles show the dose, Total brew water and Expected yield in cup, and the subtraction is spelled out beneath them. Open Advanced to change Water kept by grounds or add Bypass water added after brewing.
5. Follow the plan. Tap Start brewing for the stages and the timer.

The arithmetic is shown under The maths, in the open, and it is short:

• brew water = dose × ratio
• kept by grounds = dose × absorption
• in the cup = brew water − kept

The worked example: 18 g at 1:16 needs 288 g of water. The default absorption is 2.0 g of water per gram of coffee, so the grounds keep 36 g, and 252 g reaches the cup. Ask for 252 g in the cup under I want a cup size and the calculator works back to exactly 18 g.

The tool’s own note puts it plainly: grounds keep water, the water you pour is not the water that reaches the cup, and most calculators never subtract it.

What to watch for

Espresso has no absorption step. For espresso the ratio is dose to liquid in the cup, so nothing is subtracted. The tool’s note gives the example: 18 g at 1:2.2 is a 39.6 g shot. Taking about 36 g of retention off a shot that size would make no sense, so the tool shows the espresso note instead of a “kept” figure.

Pour targets are cumulative. For V60 and Chemex the plan starts with a bloom of 2.5 times your dose in water, then adds the remaining pours. Every target is a running total — “pour to 150 g”, not “add 55 g” — because that is what your scale reads. The last target equals the total brew water exactly. Immersion methods (AeroPress, French press, Moka pot, Cold brew) get add, steep and press steps instead, and cold brew counts its time in hours.

Two g/g is a starting point. The default of about 2 g of water kept per gram of coffee is reasonable, but coarser grinds and deeper beds keep a little more. If your scale disagrees, change Water kept by grounds in Advanced; the tool accepts values from 1.5 to 2.6 g per gram.

Every figure is a starting point to adjust to taste, not a rule. Beans, grinder, water and equipment all move the target. Grind, temperature and time appear as ranges described in generic terms; the tool carries no bean database and no named recipes from other people, so treat its guidance as a place to begin and change one thing at a time.

Impossible combinations are refused, not hidden. At a very low ratio the grounds would keep every drop and nothing would reach the cup, and the calculator says so instead of returning a negative dose.

FAQ

Why do I get less coffee in the cup than the water I poured?

Ground coffee absorbs and retains water. At the default of 2 g per gram, 18 g of coffee keeps 36 g, so 288 g of water gives about 252 g in the cup.

Does the same subtraction apply to espresso?

No. Espresso’s ratio is dose to liquid in the cup, so there is no absorption step to subtract. 18 g at 1:2.2 is a 39.6 g shot.

Why are the pour targets running totals?

Your scale shows the total weight on it. “Pour to 150 g” is something you can follow while watching the scale; “add 55 g” means doing sums mid-brew. The calculator’s final target always equals the total brew water.