Lululemon and Athleta are the two heavyweights of premium women's activewear, and shoppers constantly ask which one runs bigger. Short answer: Athleta runs about half a size larger than Lululemon across leggings, tops, and sports bras. If you're a Lululemon 6, you're usually an Athleta XS or 4.
Leggings — the core comparison. Lululemon Align (size 6) has a 27" waist and 36" hip. Athleta Salutation Stash (size 6) has a 28" waist and 37" hip. Same labeled size, roughly 1" more room at Athleta. Lululemon's compression is also noticeably firmer; Athleta uses a softer hand feel with more give.
Sports bras. Lululemon uses numeric sizes (2–14) tied to underbust + cup, while Athleta uses XS–XL with explicit cup ranges (A/B, C/D, D/DD). A Lululemon size 6 C/D ≈ Athleta M C/D, but Athleta's band sits looser. If you're between sizes, size down at Athleta and up at Lululemon.
Tops and tanks. Athleta's tanks (Renew, Conscious Crop) fit true to a US 6–8 = Small. Lululemon's Swiftly and Align tanks fit closer to US 4–6 = size 6. Same body, Lululemon size 6 ≈ Athleta XS for fitted tops, S for relaxed.
Side-by-side measurement table (women's bottoms, in inches): Lulu 2 = waist 25, hip 34 | Athleta XXS = waist 25, hip 34.5. Lulu 4 = 26 / 35 | Athleta XS = 26.5 / 35.5. Lulu 6 = 27 / 36 | Athleta S = 28 / 37. Lulu 8 = 28.5 / 37.5 | Athleta M = 29.5 / 38.5. Lulu 10 = 30 / 39 | Athleta L = 31 / 40. Lulu 12 = 32 / 41 | Athleta XL = 33 / 42.
Fit notes from reviews. Athleta consistently gets called out for being more forgiving through the waistband and easier on the hips — a better pick if you carry weight in the midsection or hips. Lululemon Align is the gold standard for a 'second skin' feel; the Wunder Train and Fast & Free run firmer and slightly smaller than Align in the same numeric size.
Inseams. Both brands offer 23", 25", and 28" inseams in most leggings. Athleta also stocks Petite (shorter rise + 21" inseam) and Tall (31" inseam) in more silhouettes than Lululemon, which is the main reason taller and shorter shoppers default to Athleta.
Bottom line. If you wear a Lululemon size 6, start at Athleta size 4 or XS for fitted styles, size 6 or S for relaxed. If you wear an Athleta M, expect to need a Lululemon 8. Always cross-check the product page measurements — both brands list cm/inch values per item, and that's still the most reliable signal.
Want exact conversions across brands? Use SizeHub's brand size charts for Lululemon and Athleta side by side, or open the size converter to translate any measurement.