What this calculator does
Find out how much ground coffee to use for the water you have, or how much water suits your coffee. The biggest single thing that shapes how coffee tastes is the ratio of coffee to water. Too little coffee and the brew is thin and sour. Too much and it turns heavy and bitter. Brewers write the ratio as 1:x, meaning one gram of ground coffee for every x grams of water. A milliliter of water weighs about a gram, so you can measure the water by volume or by weight.
This calculator works in whichever direction you need. Tell it how much water you'll brew with, how many cups you want, or how much coffee you have. It fills in the other side using a brew method's typical starting ratio, or one of your own.
Where it's used
Why this math matters outside the classroom:
- Pour-over. At a 1:16 ratio, 20 g of coffee calls for 20 × 16, which is 320 g of water.
- Working backward. With 500 g of water at 1:15, the coffee needed is 500 ÷ 15, which is about 33 g.
- Equivalent ratios. Students see 1:16, 20:320 and 25:400 as equivalent ratios on a ratio table.
- Batch brewing. Cafés scale a tested cup up to a large urn by keeping the same coffee-to-water ratio for every batch.
- Cold brew. Cold brew makers start with a much stronger ratio, such as 1:8, then dilute the concentrate before serving.
Grade level and standards: Grade 6; Common Core State Standards for Mathematics 6.RP.A.3, 6.RP.A.1. © Copyright 2010. National Governors Association Center for Best Practices and Council of Chief State School Officers. All rights reserved.
How to use it
- Choose a brew method, or Custom ratio to enter your own 1:x value.
- Choose what you know: the water amount, the number of cups (and their size), or the amount of coffee.
- Enter the amount. You'll get the coffee in grams (with a rough tablespoon count) or the water in milliliters, fluid ounces and cups.
- Brew, taste, and adjust the ratio one step at a time. A lower x is stronger; a higher x is weaker.
What the inputs mean
- Brew method
- The presets are common starting points, not rules: 1:16 for pour-over and drip, and 1:15 for French press. Cold brew concentrate, which you dilute later, starts at 1:5, and espresso at 1:2.
- Water per 1 part coffee (1 : x)
- The water side of 1:x. Most hot brews fall between 1:14 and 1:18.
- Water
- The water you pour over the grounds. For espresso, it's the weight of the finished drink, called the yield.
- Size of each cup
- Coffee makers often count a 'cup' as 5–6 fl oz, while a typical mug holds 8–12 fl oz. Use the size you actually drink.
Formula and method
coffee (g) = water (g) ÷ x water (g) = coffee (g) × x water (g) ≈ water (mL) in the cup ≈ water − 2 × coffee
In the formulas, x is the water side of your 1:x ratio, g means grams and mL means milliliters. A 1:x ratio says the water weighs x times as much as the coffee. So dividing the water by x gives the coffee, and multiplying the coffee by x gives the water. A milliliter of water weighs very close to 1 gram. That's why grams and milliliters can be swapped for water.
Used grounds stay wet, holding back roughly twice their dry weight in water. The last line is a rough estimate of what ends up in the cup or jar. For espresso, the ratio already describes the drink's weight, so no adjustment is shown.
Worked example
You want to brew 500 mL of water as a pour-over at 1:16.
- Coffee = 500 g ÷ 16 = 31.25 g.
- The grounds hold back about 2 × 31.25 = 62.5 mL. So roughly 500 − 62.5 = 437.5 mL reaches the cup.
Result: Use about 31.3 g of ground coffee (roughly 6 level tablespoons) for 500 mL of water. Expect about 438 mL of brewed coffee.
Understanding the result
If the cup tastes weak or sour, use a smaller x (more coffee) or a finer grind. If it tastes harsh or bitter, use a larger x or a coarser grind.
Cold brew concentrate at 1:5 is meant to be diluted with water or milk before drinking, often about one to one.
Assumptions and limitations
- Water is taken as 1 g per mL. Hot water is very slightly lighter, which makes no practical difference.
- Cups and fluid ounces are US measures (1 fl oz = 29.5735 mL).
- Grams per tablespoon (about 5) and the water soaked up by the grounds (about 2 g per g) are rough averages.
- Grind size, water temperature, brewing time and the coffee itself all change strength and flavor as much as the ratio does.
- A tablespoon of ground coffee weighs very different amounts depending on the roast and grind. Weigh the coffee for results you can repeat.
- The presets are typical starting points, not standards. Many people prefer 1:15 to 1:17 for pour-over and anywhere from 1:4 to 1:8 for cold brew.
Frequently asked questions
How much coffee do I need for one 8 oz cup?
An 8 fl oz cup is about 237 mL of water. At 1:16, that's about 14.8 g of coffee, or roughly 3 level tablespoons. At 1:15, it's about 15.8 g.
Does 1:16 mean weight or volume?
Weight: 1 gram of coffee to 16 grams of water. Since a milliliter of water weighs about a gram, you can measure the water in mL. Ground coffee should be weighed, because how much space it takes up depends heavily on the grind.
Why is the espresso ratio so small?
Espresso ratios compare the dry coffee (the dose) with the weight of the drink that comes out, not with the water used. An 18 g dose pulled at 1:2 gives about a 36 g shot.
How strong should cold brew concentrate be?
A 1:5 concentrate is a common starting point. You dilute it before serving, so the drink you sip is weaker. Steeping longer or using a finer grind also makes it stronger.
How this calculator is checked
Method: Definition of a mass ratio; water density taken as 1 g/mL. Brew-method ratios are common starting points used by home brewers. The calculation is covered by automated tests with known reference values and edge cases. Last updated 2026-10-18. Found a problem? Tell us.
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