When getting into nitro coffee and draft coffee, it is important to know all of the costs involved. Since it is recommended that coffee be served using nitrogen, you'll want to know how many keg (or cups) can be served using a tank of nitrogen. While we won't be able to answer this 100% accurately due to the varying sizes of kegs, nitrogen tanks and different draft pressure settings, we can give you some guidelines based on our experiences.
In this example, we're going to assume that we're serving 5-gallon kegs. Our most common size nitrogen tank is 20CF (cubic feet), and in our experience, this size tank will typically serve 6-8 kegs off cold brew and/or nitro coffee. We have heard customers say that they've gotten as many as 13 kegs out of a tank this size, so we just use 6-8 kegs as a guideline. There can also be some fluctuation if you are serving more nitro coffee than flat cold brew, and vice versa.
Obviously when serving more nitro coffee, you will use a lot more nitrogen as you are pressurizing your kegs upwards of 40psi vs when serving more flat cold brew coffee you are serving at much lower pressures (around 4-8psi) saving a lot more nitrogen. So if you serve more flat cold brew coffee, your nitrogen tank will last longer than if you were to be serving more nitro coffee on draft.
Note that pre-infusing kegs with nitrogen for serving nitro coffee will decrease the total number of kegs that you'll be able to serve, since infusing the keg is generally done in the range of 40-50psi. One way to save nitrogen when serving nitro coffee is by installing a nitro infuser. The nitro infuser removes the need to pre-infuse your coffee with nitrogen and it also operates at a lower pressure (28psi vs 40psi+).