If you’ve ever had to figure out how many bottles of alcohol to buy for your dinner party or how many drinks you’ve had over the course of an evening, you know that sometimes the math can be difficult. I’m sure you’ve found yourself asking: What is the standard size of a drink? How much alcohol is that? How much liquid is in each different bottle size?

Breathe! All you need is a little basic math and background knowledge to figure this out. Most importantly, you must remember that in the U.S., a standard drink has 14 grams of pure alcohol. Don’t get into a tizzy if math isn’t your thing though. It’s really easy, just start slow.

First, guesstimate how many drinks you’ll need for your party. As a general rule, assume guests will have two drinks during the first hour of the party, and one drink every hour after that.

Number of guests x Estimated number of drinks per guest = Total number of drinks

Next, figure out how you want to divide those drinks among wine, beer, and liquor. An easy way is to just allocate a third of the total number of drinks to each type.

Once you’ve done that, all that is left is knowing how many drinks are in each bottle size.

So that you don’t have to memorize all the quantities, here is a list of common bottle sizes and how to divide their quantities into individual drinks.

## Wine

Many people will say that a bottle of wine has 4 glasses, but that’s simply not true. If you’re pouring glasses with standard measurement, a 750-ml bottle of wine actually contains 5 servings.

So next time you need to know how many bottles of wine to buy, just divide the number of wine drinks you’ll need by 5.

## Magnum of Wine

Magnums make math easy.

A magnum is 1.5 liters of wine or twice as much as you’ll find in a standard bottle. Therefore, when purchasing for a party, divide the number of drinks you’ll require by 10.

## Can or Bottle of Beer

There’s nothing fancy here – no mixing or division. A standard can or bottle of beer is 12 ounces or one standard drink.

The good news is that drinking beer makes it easy to track the number of drinks that you’ve had.

## Beer Bomber

A beer bomber is an extra large bottle of beer. Weighing in at 22 ounces, these mega-large bottles are almost double the standard size. So if you’re in the mood for a party, these will be your go-to.

Just make sure you have a koozie so that they don’t get warm.

## Keg of Beer

If you’re having a crowd over, you’re probably going to want to invest in a keg. Unfortunately, keg sizes are not standardized.

However, you can have a pretty good idea if you know that generally, U.S. half-barrel kegs are 15.5 gallons and quarter-barrels contain 7.75 gallons. So, if you are using 10-ounce cups, slightly smaller than a traditional 12-ounce bottle, you will have 200 servings and 100 servings of beer, respectively.

## Fifth of Liquor

The fact that standard 750-ml bottles are called fifths is a remnant of the past when this measurement indicated that these size bottles were a fifth of a gallon. Now, the 750-ml bottles are technically a metric fifth, which is 1 percent smaller than its Imperial counterpart.

That being said, what you really need to know is that mixed drinks have a 1.5-ounce (45 ml) serving of liquor per drink, so a 750-ml bottle will make about 16 drinks.

For the math, you’re going to simply need to divide the number of liquor drinks needed by 16 to know how many bottles to buy.

## Handle of Liquor

A handle of liquor is 1.75 liters, which is 30 standard drinks.

So, just like with any other measurement, divide the number of drinks by 30 to determine the number of bottles you will need to purchase.

## Mini Liquor Bottles

Those fun little bottles that you get for party favors sometimes are 50ml. That means that they are only slightly over the size of a standard shot. So if you find yourself with one of these and no mixer, that’s okay.

Go ahead and have some fun with it. Bottoms up!