A relaxed fit and an accidentally-too-big shirt look similar on a hanger but feel completely different once worn. The difference is whether the extra room was a deliberate choice made with real numbers, or a guess that happened to land loose.
What “sizing up” actually adds
Using our own manufacturer spec as a real example: moving up one size (say, Medium to Large) adds about 1 inch of flat chest measurement (2 inches to the full chest circumference) and roughly 1 to 1.25 inches of body length. That’s a specific, modest amount of extra room — enough to read as a genuinely relaxed, boxier fit without crossing into “swimming in it” territory. The full breakdown by size is in Youth Tee Sizes in Inches.
How to decide if sizing up is the right call
Start from an actual measurement, not a guess. Measure a tee she already owns and likes the fit of, compare that number to the size chart, and then decide deliberately: true-to-measurement fit if you want the standard silhouette, one size up if you’re specifically after a looser, more relaxed drape.
When sizing up works well — and when it doesn’t
Sizing up tends to work best when the goal is an intentionally relaxed, boxy silhouette — the kind that’s meant to look loose on purpose. It tends to work less well if the goal is just “more room to grow,” since a shirt sized up specifically for growing room can look noticeably oversized in the meantime, rather than relaxed on purpose.
Fit attribute, not just a size swap
This is also why we tag pieces with a Relaxed or Boxy fit attribute directly, rather than leaving it to a size-up guess — it’s a real styling choice built into specific pieces, using the actual garment measurements rather than “buy a size big and hope.”
Common questions
Using our own spec, one size up adds roughly 1 inch of flat chest measurement (2 inches to full chest circumference) and about 1 to 1.25 inches of body length. It’s a specific, modest increase, not an arbitrary “buy it big” guess.
Not really — sizing up on purpose for a relaxed silhouette is a styling choice made against real current measurements. Buying larger purely for future growth tends to look oversized in the meantime, which is a different goal with a different tradeoff.
Measure a shirt that already fits the way you like, compare it to the actual size chart, and decide from there — true-to-measurement for a standard fit, one size up if you specifically want a looser, more relaxed drape.
Use the Size & Fit Guide calculator to compare your own numbers directly, or check the fit attribute (Relaxed or Boxy) listed on any individual product.