A jigger is a measuring device used by mixologists and bartenders to pour precisely 1.5 ounces (approximately 43ml) of alcoholic spirits into a drink recipe. A jigger may also have a smaller 1 ounce cup (30ml) to measure out a "pony shot," a less potent variation on the standard recipe. A metal or glass jigger is standard equipment in most bar sets, although individual gradations and capacities may vary. A British jigger, for example, may measure out 50ml and 25ml of liquid instead of the Imperial ounce.

A standard 1.5 ounce jigger provides the equivalent of a shot glass serving of alcohol. Some bartenders prefer to pour shots without measuring, however, or rely on special bottle stoppers to dispense the proper 1.5 ounces of spirits. In drink recipes, however, accuracy and ratio of ingredients can be more critical to the success of the finished product. A bartender would most likely use a jigger to measure out the different wet ingredients in a complicated drink, such as orange juice, vodka, gin, or rum. Too much or not enough of an alcoholic ingredient can ruin the balance of a mixed drink.

Some jiggers are larger than the standard shot glass standard, either to measure out non-alcoholic mixers or "doubled" amounts of alcohol in a special order. A jigger measure may also have an attached metal rod between the two cups for easier pouring into a blender or martini shaker. The mixologist should be able to tell the difference between the various sizes of cups available in a jigger set. Some jigger sets may have gradations marked on the side of the cups instead of standard measurements.

It is not uncommon for professional drink recipes to use jigger as a standard measurement. For example, a cocktail might call for a jigger of scotch and a jigger of water. If a proper jigger cup is not available, the standard 1.5 ounce measurement would still apply. A clean shot glass could serve as a jigger in a pinch, although the ratio of ingredients may change slightly. Having a reliable jigger set behind a wet bar can also settle disputes over the amount of actual alcohol a served drink contains, which can only be a good thing.