How this calculator works
A coffee is mostly water, but the emissions come from the coffee that was grown, processed and shipped, and from the milk poured into it. The life cycle figures used here are from the global food emissions study by Poore and Nemecek: roasted coffee carries about 28.5 kg of carbon dioxide equivalent for every kilogram, and dairy milk about 3.15 kg per kilogram. A latte uses roughly 18 g of coffee and 200 mL of milk, so the milk usually accounts for the larger share, even though a kilogram of coffee is far more emissions intensive than a kilogram of milk. Plant milks are much lower, from about 0.7 kg for almond to 1.0 kg for soy. The estimate leaves out the cup, the boiling of water, transport and refrigeration, so it is a floor rather than a full life cycle. It is useful for comparing habits, not for auditing a business.
Formula
annual cups = weekly cups x 52. coffee emissions = annual cups x grams per cup / 1000 x 28.5. milk emissions = annual cups x millilitres per cup / 1000 x milk factor, with 3.15 for dairy, 0.9 for oat, 1.0 for soy and 0.7 for almond. total = coffee + milk. The average per cup = total / all cups.
Worked example
Three lattes and five brewed coffees a week with dairy milk. The lattes use 3 x 52 = 156 cups a year, 156 x 18 g = 2.808 kg of coffee, which is 2.808 x 28.5 = 80.0 kg CO2e, and 156 x 0.2 L = 31.2 L of milk, which is 31.2 x 3.15 = 98.3 kg CO2e. The brewed coffees use 5 x 52 = 260 cups, 260 x 15 g = 3.9 kg of coffee, or 111.2 kg CO2e, and 260 x 0.02 L = 5.2 L of milk, or 16.4 kg CO2e. The total is about 305.9 kg CO2e a year, with 62.5 percent from the coffee and 37.5 percent from the milk.
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Frequently asked questions
Is milk or coffee the bigger part of the footprint?
It depends on the drink. A black coffee is almost all coffee emissions, while a latte with 200 mL of dairy milk can have more emissions from the milk than from the coffee. Switching milk is usually the single easiest change.
Does a reusable cup help?
It avoids the disposable cup, which the estimate here leaves out because the drink dominates. A reusable cup is still worth using, and it reduces waste as well as emissions. The bigger savings come from the milk and from not wasting the drink.
Are the emissions figures the same everywhere?
No. Coffee is grown in tropical countries and shipped, and farming methods, transport distance and processing all change the figure. The numbers are global averages from a large study, so they show the size of the choice rather than the exact footprint of one brand.
What about the energy used to boil the water?
Boiling a cup of water takes a small amount of electricity, and the emissions depend on the grid. In a province with hydroelectric power it is small; on a coal heavy grid it is larger. It is left out here to keep the comparison about the drink itself.