Why is my coffee weak and watery?

The dose, grind and ratio that make coffee taste thin, and the order to change them in.

Difficulty: beginner
Time: 10 min
Read: 2 min

Short answer

Almost always too little coffee for the water. Start at 60g of coffee per litre — about 1 heaped tablespoon per 200ml cup — and grind finer if it is still thin. Weak and bitter at the same time means under-extraction, not too little coffee.

Weak coffee has two distinct causes that need opposite fixes. Not enough coffee gives a thin, watery cup. Under-extraction — water passing through too fast or too coarse a grind — gives a thin cup that is also sour or harsh. Tasting for sourness tells you which you have.

What you'll need

Coffee
Scales (optional)
Grinder (optional)

Step by step

Weigh the coffee rather than using spoons.Scoop size varies enormously with grind and bean. Around 60g per litre of water is a solid starting ratio for filter and cafetière.
Taste for sourness before adjusting anything.Thin and flat means not enough coffee. Thin and sour or harsh means under-extraction, which is a grind or time problem.
Increase the dose first if it is simply flat.Add 10-20% more coffee and taste again. This is the fastest fix and it works for most weak coffee.
Grind finer if it is thin and sour.Finer grind slows the water and extracts more. Change one step at a time — grind adjustments have a large effect.
Check the water temperature.Around 92-96°C. Water straight off a rolling boil scalds; water below about 88°C under-extracts and tastes thin and sour.
Check the brew time for your method.Cafetière about four minutes, pour-over three to four, espresso 25-30 seconds. Short times under-extract.
Check the coffee is fresh.Ground coffee loses most of its aroma within a fortnight. Stale coffee tastes flat regardless of dose.
Check the water itself.Very soft or heavily filtered water extracts poorly and gives a hollow cup. Coffee is 98% water and its mineral content matters.

Tips

Buy a cheap set of scales before any other coffee equipment. Consistency is what makes every other adjustment meaningful.
If the coffee is too strong rather than weak, dilute the finished cup with hot water instead of brewing weaker. That is what an americano is.
Preheat the cafetière or dripper. A cold vessel takes several degrees off the water immediately.

Common mistakes

Adding more water to stretch the coffee — It dilutes an already thin cup. Adjust the dose, not the volume.
Changing grind and dose at the same time — You cannot tell which change did what, and the next adjustment is guesswork.
Using boiling water — It scalds the grounds and produces bitterness on top of whatever else is wrong. Let it stand thirty seconds off the boil.

Questions people ask

How much coffee per cup?

Around 60g per litre of water, which is roughly one heaped tablespoon per 200ml cup. Adjust from there by taste — weigh it once to see what your spoon actually holds.

Why is my coffee weak and sour?

That combination is under-extraction: water is passing through too fast, too coarse, or too cool. Grind finer, extend the brew time, and check the water is 92-96°C.