Basic Brewing Math

Keep track of basic brewing math

Brewing does involve plenty of math, but for the most part, it’s a practical kind of math. Brewing math is focused primarily on the concentration of sugars in water, which tells us how much alcohol is likely to be created from fermentation.

A Gallon of Water

  • There are 128 ounces in a gallon
  • 64 ounces in a half gallon (large growler)
  • 32 ounces in a quart (small growler)
  • There are four cups in a quart
  • There are four quarts in a gallon

How Much Does Water Weigh?

A gallon of water weighs just over 8 pounds, so when buying a kitchen scale to weigh material, look for one whose max weight is 10 pounds or so. You’ll be surprised how often you want a precise number of ounces or gallons of water when you’re brewing. (8.34 is the technical answer, so maybe “8-and-one-third-pounds” is more accurate.)

20L Kettle?

Kettles and coolers are usually described in liters, like a “20 liter stainless steel kettle.” Liters and quarts are roughly comparable, so your 20 liter stainless steel kettle = 20 qt / 4 (quarts in a gallon) = 5 gallons when full. This is certainly usable for brewing tasty beer, but if you’re making the investment, a larger kettle volume will give you the ability to do full volume boils. This gives you more control over color and can make transfers simpler.

Hydrometers, LME, and DME

Hydrometers, while not strictly necessary, give the brewer useful information about the amount of alcohol the wort + yeast can produce.

One pound of liquid malt extract per gallon will produce a gravity slightly below 1.040. Liquid malt extract – LME – is usually sold in 3.3 pound cans or jars.

One pound of dry malt extract per gallon will produce a gravity just above 1.040. Dry malt extract – DME – is usually sold in one pound or three pound bags for the home brewer’s use.