Many homebrewers enjoy using an outdoor gas burner and a propane tank for homebrewing. It’s usually faster than brewing on an electric stove and it allows you to brew outside. But how can make sure you don’t want to get caught halfway through your boil with an empty gas tank?

One method to prevent a frustrating situation is to have a spare propane tank on hand. This is definitely a good idea. But if you’re DIY-er or haven’t had that chance to exchange a tank, you might find it helpful to know whether you have enough propane to get through a brew day.

Here’s what you need in order to figure out how much fuel is left in your propane tank for homebrew day:

- a propane tank
- a scale with at least 40 lbs. capacity (for a 20 lb. tank)
- records of how many brews you’ve done since the last fill up
- a calculator

Here’s how to figure out how much propane is left in your tank:

- Weigh your propane tank.

- Check the rim of the propane tank, near the handles, for a stamp that shows the tare weight of the tank. This is usually labeled “TW.” The tare weight is the weight of the tank when it’s empty.

- Subtract the tare weight from the weight of the tank to find the weight of the fuel left in the tank.

Now, to calculate whether you have enough propane to get through a brew day:

- Determine how much fuel has been used so far by subtracting the remaining fuel from the fuel tank capacity. For example, you find that you have 5 lbs. of fuel left in the tank. Assuming the tank was a full 20 lbs. to begin with, that means you’ve gone through about 15 lbs. of fuel. (For best results, you will have weighed the tank right after you bought it to have an accurate starting point.)

- Take the amount of fuel that has been used so far and divide by how many brews you’ve done on that tank. Checking your homebrew notes, you know that you’ve done five brews with this tank. Divide the total fuel used (15 lbs.) by the number of brews (5) to arrive at how much fuel you typically use per brew (3 lbs.).

- Estimate how many brews you have remaining. Continuing with the example above, if you have 5 lbs. of fuel left and you use an average of 3 lbs. of fuel per brew, you have about 1.67 brews left in that tank (5 / 3 = 1.67). After your next brew, you should definitely refill or exchange your propane tank!

Are you curious whether propane burners save time over electric stoves when homebrewing? Check out Bryan Roth’s Water Boil ExBEERiment.

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David Ackley is a beer writer, homebrewer, and self-described “craft beer crusader.” He holds a General Certificate in Brewing from the Institute of Brewing and Distilling and is founder of the Local Beer Blog.