Great pour over coffee is mostly arithmetic. Once the water is hot and the grounds are fresh, the difference between a sweet, balanced Chemex and a sour or bitter one usually comes down to a single number, the ratio of coffee to water. The Chemex Ratio Calculator above does that arithmetic for you. Tell it how much coffee or how much water you want to start from, choose your ratio, and it returns the complete recipe, including the bloom water, the totals in milliliters, liters, cups and ounces, and the coffee measured out in tablespoons for anyone brewing without a scale.
Guessing is the enemy of repeatability. A brewer who eyeballs the coffee one morning and weighs it the next will get two different cups from the same bag of beans, and will never know which variable changed. A ratio fixes the strength of the recipe on paper, so the only things left to adjust are grind size and pouring technique. Whether you brew a single mug before work or a full carafe for the table, the calculator scales the same trusted recipe up or down without any mental math at the kettle.
How to Use the Chemex Ratio Calculator
- Choose where to start. Pick coffee amount if you know how many grams of beans you want to use, or water amount if you know how much coffee you want in the carafe at the end.
- Enter the amount. Coffee is measured in grams and water in milliliters, which weigh the same as grams on a kitchen scale.
- Set the ratio. The second number is the grams of water used for every gram of coffee, so 15 means a 1 to 15 ratio.
- Press Calculate. The tool works out the matching coffee and water amounts, the bloom water, and the same recipe in liters, cups, ounces and tablespoons.
- Brew to the numbers. Weigh the water as you pour, start with the bloom amount, then add the rest in slow spirals.
What a Coffee to Water Ratio Really Means
A ratio is simply a recipe written as a proportion. A 1 to 15 ratio means that for every one gram of ground coffee, fifteen grams of water pass through the bed. Double the coffee and you double the water, and the strength of the cup stays the same. Halve both and the cup tastes identical, just smaller. This is why ratios travel so well between brewers of different sizes, from a small three cup Chemex to the large eight cup model, and why baristas write ratios on bags and café menus instead of fixed gram amounts.
Ratio controls strength, which is not the same thing as extraction. Strength is how concentrated the finished coffee is, and it is set almost entirely by the ratio. Extraction is how much of the coffee bean has dissolved, and it is governed by grind size, water temperature and contact time. A common beginner mistake is trying to fix a bitter cup by changing the ratio, when bitterness usually signals over extraction and calls for a coarser grind. Set the ratio for the strength you enjoy, then tune the grind for balance.
The Chemex Sweet Spot
The Chemex is a forgiving brewer with a very thick filter paper, and that paper shapes the ideal ratio. The filters strip out more oils and fine particles than a metal or cloth filter, producing the clean, tea-like cup the Chemex is famous for. Because the cup is so clean, slightly stronger ratios tend to taste better than they would in a French press. Most home brewers land somewhere in this range.
- 1 to 17: the classic golden ratio starting point, light and delicate, best for bright washed coffees.
- 1 to 16: a gentle step up in body while staying firmly in filter coffee territory.
- 1 to 15: the Chemex sweet spot for many drinkers, sweet and full without heaviness.
- 1 to 14: noticeably richer, a good choice for decaf or for coffee served with milk.
- 1 to 12: strong and concentrated, closer to a pour over brewed for iced coffee.
- 1 to 10: very strong, usually reserved for flash chilled recipes poured over ice.
Start at 1 to 15 if you are unsure. Brew a cup, taste it, and move one step at a time. Changing the ratio by a single point makes a clear difference in the cup, so there is no need to jump around. Keep notes on the bag or in your phone, because the ratio that flatters a fruity Ethiopian coffee may flatten a chocolatey Brazilian one.
A Worked Example
Say you want a solid morning brew and you weigh out 30 grams of coffee at a 1 to 15 ratio. The calculator returns 450 milliliters of water in total, which is 0.45 liters, about 1.9 US cups or 15.2 fluid ounces. The bloom water, set at twice the weight of the coffee, is 60 milliliters. The remaining 390 milliliters go in after the bloom, in two or three slow pours. If you do not own a scale, the same 30 grams of coffee is about 4.3 level tablespoons, though a scale will always be more consistent from scoop to scoop.
Working in the other direction is just as easy. If your kettle holds 500 milliliters and you want every drop used at a slightly gentler 1 to 16 ratio, the calculator asks for 31.3 grams of coffee, with about 63 milliliters of bloom water. This direction suits anyone who brews a fixed carafe size and wants the coffee amount to follow the water, rather than the other way around.
Why the Bloom Matters
Fresh coffee holds carbon dioxide trapped during roasting. When hot water first hits the grounds, that gas escapes in a bubbling rise that brewers call the bloom. If you pour the full amount of water straight away, the gas pushes water off the grounds and the bed extracts unevenly, leaving some grounds overworked and others barely touched. A bloom pour of roughly twice the coffee weight in water, followed by a rest of thirty to forty five seconds, lets the gas leave before the real brewing starts.
The calculator fixes bloom water at two times the coffee weight, which suits most fresh beans. Very fresh coffee, less than a week off roast, can gas aggressively and may bloom better with two and a half or even three times its weight in water. Coffee that has sat open for a month has already lost most of its gas and needs nothing more than the standard double weight. Watch the bloom as a freshness gauge, because a lively, swelling dome almost always means the cup will taste vibrant.
Grind, Temperature and Timing
Ratio sets the strength, but three other variables decide whether the recipe tastes sweet or harsh. Grind size is the biggest lever after ratio. Chemex brews need a medium coarse grind, roughly the texture of coarse sea salt, because the thick paper already slows the drawdown. Too fine a grind stalls the filter and drags bitter flavors out of the coffee. Too coarse a grind lets water race through and leaves the cup thin and sour.
- Water temperature: aim for 93 to 96 degrees Celsius, just off the boil, for most beans.
- Total brew time: most Chemex recipes finish between three and a half and four and a half minutes.
- Pour pattern: pour in slow spirals from the center outward, keeping the water level steady.
- Filter rinse: rinse the paper with hot water before brewing to wash out any papery taste and warm the glass.
- Freshness: beans two to twenty days off roast usually give the liveliest results.
If a brew finishes in under three minutes, grind finer. If it drags past five minutes and tastes dry or bitter, grind coarser. Change only one variable per brew, and lean on the ratio to set strength, so the notes you take stay useful next time.
Scaling a Recipe Up or Down
The real power of a ratio is that it scales without distortion. A 1 to 15 recipe that tastes right at 20 grams of coffee and 300 milliliters of water tastes the same at 40 grams and 600 milliliters, as long as the grind and pour keep the brew time in the same window. In practice, larger brews often need a slightly coarser grind, because a deeper coffee bed slows the drawdown on its own. Smaller brews may need the opposite nudge.
Batch size also affects how the coffee ages in the carafe. Chemex coffee is at its best within twenty minutes of brewing, so scaling up for a crowd works only when the crowd is actually there to drink it. For a long brunch, two medium brews back to back usually beat one giant brew that sits and cools. The calculator makes those medium brews effortless, because the same ratio can be re-entered at any size in seconds.
Common Ratio Mistakes
The most common mistake is mixing up which number in the ratio is which. In a 1 to 15 ratio, the larger number is always the water. Brewers who reverse the figures end up with an undrinkably strong slurry or, more often, wonder why their coffee tastes like tinted water. The second mistake is measuring coffee by volume with scoops of varying heap, which can swing the dose by several grams between brews. The third is changing the ratio and the grind in the same brew, then having no idea which change fixed or broke the cup.
A quieter mistake is using a ratio borrowed from a different brewer. A French press recipe at 1 to 12 works because immersion brewing extracts differently and the metal filter lets oils through. Poured into a Chemex unchanged, that recipe tastes muddy and heavy. Every brewer has its own comfortable band, and for the Chemex that band sits between about 1 to 13 and 1 to 17 for hot coffee. The calculator keeps every recipe inside sensible limits and warns you when a ratio drifts outside the range where a Chemex shines.
Frequently Asked Questions
What is the best ratio for a Chemex?
Most brewers find their favorite cup between 1 to 14 and 1 to 16, with 1 to 15 as the most reliable starting point. Lighter roasted and more delicate coffees often taste better toward 1 to 16, while darker roasts and decaf usually prefer the extra strength of 1 to 14. Brew at one ratio, taste carefully, then move a single step and brew again.
How much coffee do I need for 500 milliliters of water?
At a 1 to 15 ratio, divide 500 by 15 to get about 33 grams of coffee. At 1 to 16 you need about 31 grams, and at 1 to 14 about 36 grams. Enter the water amount in the calculator with the start from water setting and it will give the exact dose along with the bloom water for your chosen ratio.
How much water do I need for 30 grams of coffee?
Multiply the coffee by the second number of your ratio. At 1 to 15, 30 grams of coffee needs 450 milliliters of water. At 1 to 16 it needs 480 milliliters, and at 1 to 17 it needs 510 milliliters. The bloom takes 60 milliliters of whichever total you choose, poured first and left to rest.
What does the bloom mean in a Chemex recipe?
The bloom is the first small pour of water, usually twice the weight of the coffee, that wets all the grounds and lets trapped carbon dioxide escape. You can see the coffee bed swell and bubble as the gas leaves. Wait thirty to forty five seconds after the bloom pour before adding the rest of the water, so extraction stays even across the whole bed.
Can I use tablespoons instead of a scale?
Yes, with a small loss of precision. A level tablespoon of ground coffee weighs roughly 7 grams, so the calculator converts your dose into tablespoons as a fallback. Scoops vary with grind size and how heaped they are, so your ratio may drift by a gram or two per spoon. A basic kitchen scale removes that guesswork and makes every brew repeatable.
Why does my Chemex coffee taste sour?
Sourness usually means under extraction rather than a wrong ratio. The usual causes are water that is too cool, a grind that is too coarse, or a brew that finished too quickly. Try a finer grind first, keep the ratio the same, and aim for a total brew time closer to four minutes. Hotter water, just off the boil, also helps pull more sweetness from the grounds.
Why does my Chemex coffee taste bitter?
Bitterness points to over extraction. A grind that is too fine slows the drawdown and keeps water in contact with the coffee for too long, dragging out harsh compounds. Grind coarser, pour a little faster, and check that the total brew time stays under about four and a half minutes. If the cup is balanced but simply stronger than you like, weaken the ratio instead.
Does the ratio change for iced Chemex coffee?
Yes. Flash chilled Chemex coffee is brewed strong, often at 1 to 10 or 1 to 12, because part of the water in the recipe is replaced by ice in the carafe and the melting ice dilutes the brew. Brew hot and concentrated directly onto the ice, using the calculator with the total water figure counting both the hot water and the ice weight together.
How many cups does a Chemex ratio make?
That depends on your mug size rather than the brewer size printed on the box. Chemex cup markings are five ounce cups, so an eight cup Chemex holds about 40 ounces or 1.18 liters. At a 1 to 15 ratio, a full eight cup brew needs roughly 79 grams of coffee. For two generous mugs of about 300 milliliters each, brew 600 milliliters with 40 grams of coffee.
Should I rinse the Chemex filter before brewing?
Yes. Chemex filters are thick and can leave a papery taste in the cup if they go in dry. Rinse the filter thoroughly with hot water, discard the rinse water, and then add your grounds. The rinse also warms the glass, which helps keep the brew temperature steady during the pour, especially in a cold kitchen.
What grind size works best with these ratios?
A medium coarse grind, similar to coarse sea salt, suits the Chemex and its thick filters. The paper already slows the flow, so the coffee bed does not need to. If the drawdown stalls and the brew drags past five minutes, go coarser. If water races through in under three minutes and the cup tastes thin, go finer. Keep the ratio fixed while you tune the grind.
How does the Chemex ratio compare with a V60 ratio?
The two brewers overlap heavily, and many recipes work in both. V60 brewers often sit between 1 to 15 and 1 to 16.5, while the Chemex, with its thicker paper and cleaner cup, often tastes best a touch stronger, between 1 to 14 and 1 to 16. If you move a recipe from a V60 to a Chemex, strengthen it by one ratio point as a starting guess.
Can I reuse a ratio for a different amount of coffee?
Yes, that is the whole point of brewing by ratio. The same proportion scales cleanly from a small 250 milliliter brew to a full liter carafe. Very large brews sometimes need a slightly coarser grind because the deeper coffee bed slows the water on its own, but the coffee and water amounts the calculator gives you stay correct at any size.
How much coffee is in a strong Chemex brew?
Strong in ratio terms means a low second number. A 1 to 12 brew of 600 milliliters uses 50 grams of coffee, while a 1 to 10 brew of the same size uses 60 grams. Strong recipes shine for iced coffee and for coffee served with milk, but they also highlight any staleness in the beans, so use fresh coffee when you brew strong.
Does water quality change the ratio I should use?
Water quality changes flavor more than it changes the ideal ratio. Very hard water can mute acidity and make a cup taste flat, while very soft water can leave it sharp. Most brewers get their best results with filtered water that tastes clean on its own. Keep your preferred ratio, fix the water first, and only adjust the ratio afterward if the cup still feels too strong or too weak.