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Chemex Ratio Calculator: Coffee & Water

Pick your Chemex size and how many 5 fl oz cups to brew to get the coffee, water, bloom and pour schedule, with a target brew time.

Build your Chemex recipe

1:16.0
Bold (1:14)Clean (1:18)

Coffee needed

4 cups

36.9g

Water

591g

Water (fl oz)

20.0fl oz

Target time

4:00-5:00

Approx. tbsp

7.4tbsp

Pour schedule (scale readings)

Bloom

74 g · 45s

Pour 1

to 333 g

Pour 2

to 591 g

Drawdown

4:00-5:00

Coffee to water by weight

Next: The thick Chemex filter drains slowly, so grind medium-coarse. Over 6 minutes means grind coarser; under 3:30 and thin means finer.

Brew this with the step timer →

The math behind the calculator

Water = cups × 5 fl oz (Chemex counts 5 fl oz cups), converted to grams. Coffee = water ÷ ratio. The bloom is about 2× the dose, and the rest goes in two pours.

The target time grows with batch size, because more coffee makes a deeper bed that drains more slowly through the thick filter.

How to use the result

  1. 1Rinse the filter (three-layer side to the spout).
  2. 2Bloom, then pour in two stages to the total.
  3. 3Lift the filter out when the drawdown finishes.

Common mistakes

  • Grinding as fine as for a V60.
  • Putting the single-layer side of the filter over the spout.
  • Counting 8 oz mugs instead of 5 fl oz Chemex cups.

What this calculator assumes

Every fixed figure the maths uses, so you can check the result against your own gear.

  • A Chemex cup is 5 fl oz (about 148 ml).
  • Water is taken as 1 g per ml.
  • Bloom water is 2× the coffee dose, left for about 45 seconds.
  • Brew times assume a medium-coarse grind and Chemex bonded filters, rinsed first.
  • A level tablespoon of ground coffee is taken as about 5 g.

What you need

The kit that makes the numbers above repeatable.

  • Chemex: sized by 5 fl oz cups: a 6-cup brews up to about 30 fl oz.
  • Chemex bonded filters: thicker than most papers, which is what gives Chemex its clean cup. Fold so the three-layer side faces the spout.
  • Burr grinder: medium-coarse, between drip and French press. Too fine and the thick filter stalls.
  • Scale with a timer: for the bloom and the two main pours.
  • Gooseneck kettle: a steady, slow stream keeps the bed level in the tall cone.
  • Fresh beans: medium and light roasts show off the clean, bright cup Chemex is known for.

Step by step

Follow along with the calculator's scale readings.

  1. Heat water to about 93-96°C (200-205°F).
  2. Place the filter with the three-layer side over the spout, rinse it with hot water, then pour that water out through the spout.
  3. Add the ground coffee, level it, and tare the scale.
  4. Start the timer and pour the bloom amount, about twice the coffee weight. Wait 45 seconds.
  5. Pour slowly in circles up to the first scale reading, keeping the water level a little below the filter rim.
  6. Pour the rest up to the total weight.
  7. Let it drain, then lift the filter out. A 4-cup batch usually finishes in 4 to 5 minutes.

Which ratio should you use?

Ratio sets strength; grind sets extraction. Change one at a time.

RatioTastesUse it for
1:15Rich, rounder bodyDarker roasts or when brewing for milk
1:16Balanced and cleanThe standard Chemex starting point
1:17Light, very clean, brightLight roasts and floral coffees

Common problems and fixes

Read the cup and the brew time, then change one thing.

ProblemLikely causeFix
Drains for 6+ minutesGrind too fine for the thick filterGrind coarser; Chemex usually needs coarser than a V60
Thin and sour, fast drawdownGrind too coarseGrind a step finer and keep the ratio
Filter collapses or seals the spoutSingle-layer side over the spoutTurn the filter so the three-layer side faces the spout
Coffee cools quicklyGlass not preheatedRinse with plenty of hot water and pour it out first
Brew tastes flat for a big batchBed too deep for the pourUse two or three pours and keep the stream slow and central

"Chemex cups are 5 fl oz, so \"6 cups\" is about three mugs. If you would rather not pour by hand, the Chemex Ottomatic brews into the same carafe automatically."

Grinders for a Medium-Coarse Chemex Grind

Chemex needs an even medium-coarse grind or it stalls. These are the filter-friendly burr grinders we rate.

Fellow Ode Gen 24.8

Fellow

Fellow Ode Gen 2 Review

A single-dose grinder built specifically for pour-over and filter coffee enthusiasts — not intended for espresso.

Baratza Encore ESP4.5

Baratza

Baratza Encore ESP Review

An electric grinder with micro-stepped adjustment and Baratza's repair-friendly design, spanning espresso through French press.

Want Chemex Coffee Without the Pouring?

Our Chemex Ottomatic review covers the automatic brewer that pours over a Chemex for you.

Chemex Ottomatic 2.04.3

Chemex

Chemex Ottomatic 2.0 Review

An automated take on the Chemex ritual, keeping the same clean, bright cup character but without the standing-over-a-kettle routine.

Frequently Asked Questions

Quick answers before you buy.

What is the best ratio for a Chemex?

1:16 is a good start, about 30 g of coffee to 480 g of water for a medium batch.

Move to 1:15 for more body or 1:17 for a cleaner cup.

How big is a Chemex cup?

5 fl oz, about 148 ml.

A 6-cup Chemex brews about 30 fl oz, which is closer to three or four mugs.

How much coffee for a 6-cup Chemex?

About 30 to 50 g, depending on how many cups you brew.

Four cups (about 590 ml of water) at 1:16 needs roughly 37 g.

Why is my Chemex so slow?

The thick bonded filter drains slowly, so a grind that works in a V60 is often too fine here.

Grind medium-coarse and aim for 4 to 5 minutes for a mid-size batch.

Do you need to rinse a Chemex filter?

Yes.

Rinsing with hot water removes the papery taste and preheats the glass.

Pour the rinse water away before adding coffee.

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