Foundational
International coffee units and measurements
Grams versus ounces, Celsius versus Fahrenheit, bar versus psi, and why a US cup, an imperial cup and a café serving size aren't the same volume.
In short
Coffee recipes arrive in whatever units their author grew up with: ounces and Fahrenheit from one country, grams and Celsius from another, and cups from everywhere, meaning something different each time. Following a recipe accurately starts with knowing which units it is written in.
CoffeeHQ's tools and recipes use grams, millilitres and degrees Celsius. This page gives the conversions, and points out the three places where a conversion alone will mislead you.
Weight: grams and ounces
Widely documented
| Variable | Typical range | What moving it does |
|---|---|---|
| 1 ounce | 28.35 g | |
| 15 g of coffee | 0.53 oz | A typical single filter cup. |
| 18 g of coffee | 0.63 oz | A typical double espresso dose. |
| 60 g of coffee | 2.12 oz | About a litre of filter coffee. |
| 250 g bag | 8.8 oz | |
| 12 oz bag | 340 g | |
| 1 lb bag | 454 g |
These are weights. A fluid ounce is a volume and a different thing: see the section on cups below.
Why a scoop is not a unit
CoffeeHQ explanation
Spoons and scoops measure volume, and the weight of coffee in a given volume changes with the coffee. A dark roast is less dense than a light one, so a level scoop of it weighs less. Ground coffee packs differently from whole beans, and fine grounds differently from coarse. The same scoop can vary by a couple of grams from one coffee to the next, which is more than enough to change the taste of a single cup.
Water has the opposite property, and a convenient one. One millilitre of water weighs almost exactly one gram, so water can be weighed on the same scale as the coffee. That is why brewing recipes give water in grams: it is a volume you can measure by weight.
Volume: the cup that is four sizes
Widely documented
| Variable | Typical range | What moving it does |
|---|---|---|
| US customary cup | 236.6 ml | 8 US fluid ounces. The cup in most American recipes. |
| Metric cup | 250 ml | Used in recipes from Australia, Canada and elsewhere. |
| Imperial cup | About 284 ml | Half an imperial pint. Found in older British recipes. |
| Coffee-maker cup | Commonly about 150 ml | The marks on many filter-machine carafes are five US fluid ounces or thereabouts, not eight. It varies by maker. |
| 1 US fluid ounce | 29.57 ml | |
| 1 imperial fluid ounce | 28.41 ml |
A café's small, regular and large are business decisions and not units at all. When a recipe says one cup, find out which cup, or convert it to millilitres once and use those.
Ratios, and grams per litre
Widely documented
| Variable | Typical range | What moving it does |
|---|---|---|
| 1:15 | 66.7 g of coffee per litre of water | |
| 1:16 | 62.5 g per litre | |
| 1:17 | 58.8 g per litre | |
| 1:18 | 55.6 g per litre | |
| 60 g per litre | 1:16.7 | |
| 1:2 for espresso | 36 g of espresso from 18 g of coffee | Measured on the drink, not the water put in. |
A ratio of 1:16 means sixteen grams of water for each gram of coffee, so a larger second number is a weaker drink. Filter ratios count the water poured; espresso ratios count the liquid in the cup, because some water stays in the grounds. The two are not directly comparable.
Temperature and pressure
Widely documented
| Variable | Typical range | What moving it does |
|---|---|---|
| Fahrenheit from Celsius | °F = °C × 9 ÷ 5 + 32 | |
| 60 °C | 140 °F | Around where steamed milk is served. |
| 90 °C | 194 °F | |
| 93 °C | 199 °F | |
| 96 °C | 205 °F | |
| 100 °C | 212 °F | Boiling at sea level; lower at altitude. |
| 1 bar | 14.5 psi | Close to one atmosphere. |
| 9 bar | About 130 psi | The conventional espresso pressure. |
Water boils at a lower temperature the higher you are, by roughly one degree Celsius for every 300 metres, so 'just off the boil' is cooler in a mountain town than at the coast.
Units you meet on water reports and refractometers
Widely documented
- mg/L and ppm
- For dilute solutions in water these are the same number: one milligram per litre is one part per million. Water hardness and alkalinity are usually quoted this way, as calcium carbonate.
- Grains per gallon
- An older hardness unit still used on some test kits and softeners. One grain per US gallon is about 17.1 mg/L.
- German degrees of hardness
- Written °dH and common on European appliance manuals. One degree is about 17.8 mg/L as calcium carbonate.
- TDS as a percentage
- On a coffee refractometer, total dissolved solids is the share of the drink that is dissolved coffee: a little over one per cent for filter coffee, commonly cited as about 1.15 to 1.45, and several times that for espresso. The same abbreviation on a water meter means dissolved minerals in mg/L. They are different measurements with one name.
What to do next
- Coffee ratio and strength calculator — Does the ratio arithmetic for any dose or batch size.
- Brew recipe scaler — Scales a recipe to a different number of servings without changing its ratio.
- Coffee-to-water ratio — What the ratio does to the cup, once you can read one.
- International café ordering conventions — How drink names and sizes change between countries.