The shot count, not the cup, sets the caffeine
A latte is espresso and steamed milk, and Starbucks pulls a fixed number of shots per size. Each shot of its signature espresso carries 75 mg. Short and Tall lattes get one shot (75 mg); Grande and hot Venti get two (150 mg). So a hot Venti, 20 oz, has exactly the caffeine of a Grande, and a Tall exactly that of a Short. The bigger hot size buys more milk, not more caffeine.
The iced latte breaks the pattern. The iced Venti is a 24 oz cup with three shots, 225 mg, one more than the hot Venti.
Much less than brewed coffee
A Grande latte has less than half the caffeine of a Grande Pike Place Roast (315 to 390 mg), and less than a Grande Cold Brew (205 mg). Against home coffee it lands between one and two 8 oz cups of drip coffee at USDA’s reference strength (95 mg each).
The flavoured lattes follow the same shot structure: a Grande Pumpkin Spice Latte, White Chocolate Mocha or Caramel Macchiato carries the same 150 mg. The exceptions use different espresso. A Grande Blonde Vanilla Latte has 170 mg, because blonde shots carry 85 mg each, and a Grande Flat White, made with ristretto shots, has 195 mg.
Adding it to your day
Two Grande lattes, 300 mg, leave 100 mg of the 400 mg daily figure the FDA cites for healthy adults. At 150 mg, a Grande is also under the 200 mg that EFSA assessed as a safe single dose for healthy adults.
In pregnancy, working to the 200 mg daily ceiling ACOG uses, one Grande latte leaves 50 mg for the rest of the day: about a Grande Starbucks hot chocolate (25 mg) and an ounce of dark chocolate (23 mg). A Tall latte, at 75 mg, leaves far more room.