Theory Sizing: Does Theory Run Small, Big or True to Size?

Theory does not run uniformly small or large; the size chart is a starting point, and each cut needs its own fit read. The official chart maps US numeric sizes 00 through 18 to alpha XS through XXL, with short, regular, and long inseams for bottoms. Those inseam bands are 26 to 29 inches, 30 to 33 inches, and 34 to 35 inches, so long is the brand's stated length option. The chart does not show a separate plus-size range; Bloomingdale's Rib Knit Slim Fit Cardigan has a P option, but available sizes are style-specific. The search for a theory size chart is only useful if you also check garment fabric and product-level notes. Bloomingdale's marks its Classic Straight Pants and Fluid Flare Pants true to size, while its Wide Leg Pants have a relaxed cut and are also marked true to size. Shopbop's Demitria Trousers model is shown in size 2 though she usually wears 0, and the Crew Neck Knit Dress model is shown in S though she usually wears XS. Those are individual page examples, not a brand-wide order to size up or down. Measure your waist, hip, and preferred inseam, then compare the exact fabric and shape with a garment that already fits.

Start with the trousers, because rise and inseam change how the same waist size feels. Shopbop's Demitria Trousers have low-stretch suiting and a 35-inch inseam; the model is shown in size 2 though she usually wears 0. Wide Pleated Trousers use low-stretch wool, with a 12.5-inch rise and 30.25-inch inseam; its model note is also a size 2 versus a usual 0. That is useful context, not a brand-wide reason to size up. Bloomingdale's Wide Leg Pants are true to size with a relaxed fit and a 29-inch inseam, while Fluid Flare Pants are true to size with a 32-inch inseam. Together, the examples put a low-rise long trouser, a higher pleat, a relaxed wool leg, and a longer flare side by side. Measure a pair you like at the waistband and along the inseam, then match the waist first and hem length second. The chart's Short, Regular, and Long labels can help, but the style page decides which length is actually available.

Knits are where fabric and ease do most of the talking. The Shopbop Cashmere Crew Neck Sweater is 100% cashmere in a lightweight stretch knit; its model is shown in M though she usually wears XS to S. The Purl Henley Long Sleeve Tee is a lightweight super-stretch cotton-modal jersey, and the size S model usually wears XS, so use its 22.75-inch body length as one clue, not an order to size up. Bloomingdale's Wool Crewneck Sweater Shell is sleeveless, 100% wool, and marked true to size; the Rib Knit Slim Fit Cardigan Sweater is a long-sleeve, hip-length viscose blend also marked true to size. Those aren't interchangeable: the shell is a base layer and the cardigan gives more coverage. If you plan to layer, compare bust and shoulder measurements and decide how much ease you need. Don't force a close fit if it pulls across the shoulders or makes the sleeve uncomfortable.

The dress names are less helpful than their fabrics and lengths. Shopbop's Crew Neck Knit Dress is 100% merino with stretch and measures 52.25 inches; its model wears S though usually XS. Square Neck Seamed Dress is a stretch linen-viscose weave with a hidden side zip and 46.75-inch length. Bloomingdale's Sleeveless Mock Neck Wool Dress is 100% virgin wool, marked true to size, and measures 32.75 inches. Its Short Sleeve Button Down Midi Dress is polyester, designed for midi length, and marked true to size in product data, but the sole review says it runs large. My verdict: Theory works for shoppers who compare measurements, stretch, and intended length rather than betting on a label alone. Skip a rushed order if the fit notes conflict or you cannot return or alter it. Start with a cut you already understand, check how the neckline and waist align on your body, and let the specific fabric decide whether another size makes sense.