The short answer
A plain Greek yogurt cup of about 170g typically carries 15–18g of protein, against roughly 5–8g in the same amount of regular yogurt — that gap is what you are buying. Beyond protein, compare cup weight, added sugar, and fat level, and confirm the product is genuinely strained rather than "Greek-style."
What the straining is for
Greek yogurt is regular yogurt with much of the whey strained off. Removing whey concentrates the protein, which is why the same cup weight delivers two to three times the protein of unstrained yogurt, and why Greek yogurt tastes tarter and thicker. Straining also removes some lactose along with the whey, so plain Greek yogurt usually shows less total sugar than plain regular yogurt — typically around 5–7g per 170g cup instead of 11–12g. Both numbers are lactose, not added sweetness.
Greek-style is not the same as Greek
Some products skip the straining and simulate thickness with corn starch, gelatin, pectin, or milk protein concentrate. The clue is in the ingredients: a truly strained yogurt lists milk and live cultures and little else, while a Greek-style product lists thickeners. The protein line confirms it — a thickened 170g cup often shows 8–12g of protein rather than 15–18g. Greek-style products are not necessarily bad; they are just a different product wearing the same shelf label, and they should not win a protein comparison they have not earned.
Separate lactose from added sugar
Because yogurt is made from milk, total sugars always contains lactose, so total sugar alone cannot tell you whether the product was sweetened. On U.S. labels, added sugars is indented beneath total sugars. A plain cup can show 6g total sugar with 0g added; a vanilla cup can show 15g total with 9g added — roughly the same story as three teaspoons of sugar stirred in. Read the two lines together, and remember that the lactose portion shrinks a little in strained yogurt because some of it drains off with the whey.
Check the cup weight before the lid claims
Single-serve cups look interchangeable but commonly hold anywhere from 150g to 170g, and large tubs list a 3/4-cup (170g) serving you will not measure at 7 a.m. A higher protein number can simply describe a larger cup. Compare the cup you plan to finish first, then normalize to protein per 100g if sizes differ: 15g per 170g is about 8.8g per 100g. This two-view habit prevents a size difference from impersonating a nutrition advantage.
Worked yogurt example
Yogurt A is a plain cup: 170g, 15g protein, 120 calories, 12g total sugars, 0g added sugars. Yogurt B is flavored: 150g, 14g protein, 130 calories, 16g total sugars, 8g added sugars. A gives slightly more protein in a larger cup with no added sugar; B's extra 4g of total sugar understates the real difference, because 8g of B's sugar was added while all of A's is lactose. The labels are close enough that taste and price can legitimately decide — but only after the sugar lines are read as two different facts, not one.
Fat level is a separate dial
Nonfat, 2%, and whole-milk Greek yogurts usually share similar protein per cup; what changes is fat and therefore calories. A nonfat 170g cup sits around 90–120 calories while a whole-milk version can reach 160–190. Whole milk also means roughly 4–5g of saturated fat per cup against essentially none in nonfat. Pick the fat level that matches the rest of your day rather than assuming protein comes only with the nonfat version — it does not.
Mix-ins change the product, not just the flavor
Fruit-on-the-bottom, honey, granola, and chocolate pieces add sugar and calories that belong to the comparison. A flavored cup plus a separate bag of granola is not the same purchase as a plain cup, and "I will add my own fruit" only counts if you actually do it. Compare plain with plain and flavored with flavored; if you are weighing a pre-flavored cup against plain yogurt plus toppings at home, put both toppings into the scenario, including their price.
When both cups look reasonable
If protein and added sugar are within a gram or two, the honest tie-breakers are price per cup, which texture you prefer, and whether you will finish the size you bought. Store brands frequently match national brands gram for gram at a lower price — check per 100g rather than trusting the tub size. And if the difference that remains is one rounded gram on the label, call it tied and buy the one you enjoy; rounding alone can manufacture gaps that size.
What this comparison cannot tell you
Label math cannot rank protein quality, probiotic benefit for your situation, or whether yogurt fits a medical diet. For milk allergy, lactose intolerance severe enough to need avoidance, pregnancy, or a clinician-set diet, the package allergen statement and professional advice come first. Label lines themselves are defined in the FDA's Nutrition Facts guidance and its added-sugars page. Recheck cups after packaging changes — reformulations are common in this category.
In the dairy aisle, AptBite can scan two cups, normalize them to the same weight, and show protein against added sugar without flattening the trade-off into a score.
