Both the rocks glass and double old fashioned, or “DOF,” are standard issue behind any well-stocked bar, and together they’ll cover just about any spirit or cocktail on your menu. But do you know the difference between the two – and when you should use them? Read on to find out: 

The rocks glass 

The rocks glass is also known as an old fashioned, named for the OG cocktail of the same name. Sometimes called a lowball, this short, sturdy glass clocks in at around 6 to 10 ounces, with a wide mouth and thick, balanced base ideal for muddling.  

Traditionally, an old fashioned was always served in cut glass, though today’s rocks glasses come in an endless variety of designs.  

Rocks glasses are preferable (naturally) for on-the-rocks cocktails built directly in the glass, as well as straight spirits and neat drinks. Other popular rocks cocktails include the Negroni (on the rocks), the mint julep and the classic Sazerac. 

The smaller capacity of the rocks glass is perfect for high-proof, spirits-forward drinks, meant to be enjoyed in slow, measured sips.  

The double old fashioned 

Despite its name, the double old fashioned is not necessarily twice the size of a traditional old fashioned glass, but at 12 to 14 ounces, it is significantly larger.  

If you could only have one glass behind your bar, this would be it: The versatile double old fashioned can serve anything from a straight pour of your favorite spirit to martinis to mixed drinks. A single ice cube can be added to unlock the complex flavor of dark spirits like whiskey and bourbon. 

Still, with its volume, the DOF is ideal for lower-alcohol cocktails that feature lots of ice and mixers, like a creamy white Russian or tiki-style drinks like the Mai Tai. This is the glass of ordering round after round.