A jigger is a double-sided measuring vessel — typically with a 1.5 oz (standard pour) cup on one end and a 0.75 oz cup on the other, though sizes vary by jigger. It's used to measure every liquid ingredient in a cocktail before it goes in the shaker or glass. A jigger is not optional equipment — it is the single most important tool for making consistent drinks. Even experienced bartenders who can "freehand" pour accurately do so because they've poured the same measures thousands of times. Until you have that experience, the jigger is how you learn the ratios that make cocktails work.
Why It Matters
Even a quarter-ounce difference in a sour recipe changes the balance of the drink noticeably. Without a jigger, you're guessing — and cocktails don't reward guessing the way cooking sometimes does. A jigger costs almost nothing and eliminates the single biggest variable in cocktail quality.
Where You'll Use It
Every cocktail. Every time.