The Margarita is the classic example of what limits batching: fresh citrus oxidizes. A bottled Negroni holds for a month because nothing in it can spoil. A pitcher of Margaritas holds for two days because the lime starts to brown and flatten within hours. That's not a flaw — it's the design constraint. A Margarita pitcher exists for the situation where you know how many drinks you'll pour, and roughly when.
The lime in a fresh Margarita is a clock. Pitchering it just lets you start the clock earlier.
— Practical batchingThe ratio is 2:1:0.75:0.25
Two ounces tequila, one ounce Cointreau, three-quarters of an ounce fresh lime juice, a quarter-ounce of simple syrup to round the citrus. This is the Margarita the canonical bars pour. The pitcher scales it linearly: ten drinks means twenty ounces tequila, ten ounces Cointreau, seven and a half ounces lime juice, and two and a half ounces simple syrup.
Use a 100% agave silver or blanco tequila — Espolòn, Lunazul, El Tesoro, anything with a real backbone. Cointreau over generic triple sec, every time; the cost difference per drink is pennies and the aromatic difference is enormous.
Lime: the limiting factor
Fresh lime juice begins oxidizing within hours. At 48 hours refrigerated it's drinkable but flat; at 72 it's noticeably off. Squeeze the limes the morning of service, or — for longer shelf life — substitute Lime Super Juice (see /ingredients/lime-super-juice/), which holds for 2-3 weeks and is indistinguishable from fresh in this context.
Service
Stir the pitcher with a long spoon. Salt the rim of each rocks glass; pour 4 oz over ice. Garnish with a lime wheel. The pitcher's pre-mix replaces the shake, which the lime juice would have aerated; the dilution you'd expect from shaking is built into the ratio above.
Don't add ice to the pitcher itself — it'll over-dilute as the party slows down. Keep the pitcher refrigerated; pour over individual glassware ice.