Moka Pot Coffee and Water Calculator

The moka pot is deceptively simple — a bottom chamber fills with water, steam pressure pushes it through a coffee basket, and espresso-strength brew collects in the top chamber.
But the dose matters more than most people realize.

Underdosing (too little coffee) produces a watery, bitter cup because the water blasts through the puck too fast with too little resistance.
Overdosing (packing the basket too full) restricts flow, builds excess pressure, and can cause sputtering or an uneven extraction.

Here is the part that trips people up: on a moka pot you do not choose the dose. The basket does. Fill it level and full, every time, no tamping, and the dose is whatever that basket holds. A Bialetti 3-cup basket takes about 16 grams, a 6-cup about 30, a 9-cup about 45, a 12-cup about 60. That works out near 5 grams per nominal cup, and paired with a boiler filled to just under the valve it lands the brew around 1:9, which is the ratio moka has always run at.

Keep in mind that moka “cups” are espresso-sized, roughly 40 to 60 ml of finished brew, not the 240 ml you would pour into a mug. A 3-cup pot makes something like 110 ml in total: three small servings, or one respectable American-sized coffee.

Basket and boiler volumes vary a little between brands and between the aluminium and stainless lines, so treat the millilitre figures here as Bialetti-shaped estimates. The two physical rules are what actually matter, and they are the same on every pot: level-full basket, water to just below the valve.

Water fill: fill the bottom chamber to just below the safety valve.
Never overfill — the valve is there to release excess steam pressure, not to indicate the fill line.
Most bottom chambers have a fill line or a visible bottom of the valve; use that.

Grind size matters a lot.
Too fine (espresso grind) and the puck packs too tight — slow extraction, sometimes no flow at all.
Too coarse (drip grind) and the water rushes through without proper resistance, producing a thin brew.
Target a medium-fine grind: slightly coarser than espresso, finer than drip.
If all you have is pre-ground espresso it will still work, but expect a slower, fussier extraction, and definitely do not tamp it.

For a stronger cup, take water out rather than putting coffee in.
The basket is already level-full at the standard setting, so there is nowhere for extra grounds to go, and cramming them in is exactly the overdosing that causes sputtering. Dropping the water level a centimetre concentrates the same coffee into less brew, which is the lever the strength setting above pulls.
Grinding a touch finer works too, though it is fussier: go too far and the puck chokes.