Between Sizes: Should You Size Up or Down in Knit Tops?

Between sizes on a knit top? The short answer: size up. Knitted fabric stretches across the body but the shoulders, neckline and seams cannot shrink to fit you — a knit that is slightly loose drapes the way the designer intended, while one that is half a size too small pulls at the closure, rides up at the hem and shows every line underneath. The one exception: a deliberately relaxed cut with generous ease, where staying at your measured size keeps the intended silhouette. Every RUIJIN product page flags its fit as petite-friendly and says the same thing — between sizes, go up. Here is how to decide in thirty seconds, with real examples from the current collection.

What does "between sizes" actually mean?

You are between sizes when your measurements sit in the gap between two rows of a size chart — for example, a 92 cm bust where size S tops out at 90 cm and size M starts at 94 cm. It is not a fitting failure; it is arithmetic. Size charts use fixed steps (usually 4–6 cm between adjacent sizes), and real bodies do not move in neat increments.

The gap shows up most often in two places: the bust on fitted knits, and the waist on tailored trousers. It also appears when your top and bottom measurements would put you in different sizes — a common pattern for petite frames, where the bust may fall in S while the waist sits closer to M. That is why the question "should I size up or down" has no single answer until you have actually measured. If you have not measured yourself recently, the five-minute guide on how to measure yourself for womenswear is the fastest fix.

Should you size up or down in knit tops?

For knit tops, size up. Three reasons, in order of importance:

• Knits give horizontally, not at the edges. A knit fabric can stretch 5–10% across the bust and still recover, but the shoulder seam, neckline rib and armhole are fixed points. Size down and those fixed points sit slightly off your frame; size up and everything stays where the pattern intended.
• A too-small knit shows what you wear under it. In hot, humid weather you want air between the fabric and your skin. A knit at exactly your measurements clings; one with a centimetre of ease breathes and moves.
• Knits relax with wear anyway. Fine-gauge cotton, Lyocell and viscose blends open up slightly over a day of wear. If you start at the smaller size, by afternoon the fit that was "snug but fine" at 9am is straining at the shoulder by the commute home.

The Seamless-Knit Short-Sleeve Top ($32.99, sizes S–M) is a textbook case: a slim, second-skin cut in a Lyocell blend. Its product page says exactly what this article argues — it runs petite, and if you are between sizes you should take the larger one. The fabric will skim, not cling.

When should you stick with your usual size?

Size up is the default for fitted knits, not a universal rule. Stay at your measured size — or even accept the smaller one — in these situations:

• The cut is already relaxed. Wide-leg trousers, boxy shirts and "relaxed proportion" pieces carry design ease built into the pattern. The High-Waist Wide-Leg Pants with Fluid Drape, for example, are cut with volume through the leg; sizing up there adds fabric without adding comfort.
• The waist is elastic or drawstring. Pieces like the Effortless Straight-Leg Pants with Elastic Waist forgive a centimetre of gap at the waist, so the smaller size stays comfortable.
• The fabric is a firm weave, not a knit. Ramie and linen shirting (100% ramie in the relaxed minimalist shirt, for instance) barely stretches — but woven shirts are also cut with more room through the body than a fitted knit. Follow the size chart, not the "size up" instinct.

One honest note on the current collection: one two-piece knit set is offered in a single "One size" with generous cut. There is no between-sizes decision to make there — check the garment measurements on the product page instead of the letter on the label.

How does a petite fit change the decision?

All 24 styles in the current RUIJIN collection flag their sizing as petite-friendly on the product page, and most knit tops are offered in S–M. That changes the between-sizes math in two ways.

First, petite cuts are shorter through the torso and sleeve. A knit that fits your bust but hangs past your hip is the wrong proportion even when the measurements "work" — and sizing up makes the length problem worse, not better. When a fitted petite-cut knit sits between sizes for you, the larger size plus a front tuck into high-waisted trousers usually beats the smaller size plus a strained shoulder line.

Second, most knit tops stock S and M only, so the gap between available sizes is doing more work per step. Where a full-size-range brand might land your bust exactly on an M, a two-size knit top forces the S-or-M call more often. The pieces that do run broader — the Cap-Sleeve Crew Knit Top in M–XL, and trousers in S–L — give you a finer ladder to climb, which is worth checking before you assume every style stops at M.

Does fabric stretch change the answer?

Somewhat — fabric decides how forgiving each direction is. Ribbed knits and blends with a synthetic share (the striped polo knit at 29.6% acrylic and 40.8% polyester, or the 85% viscose cardigan) snap back to shape, so the larger size will not sag out after three wears. Looser-gauge cotton and linen knits relax more and recover less, which is another argument for the larger size: start with ease and let the fabric settle toward you, rather than starting tight and hoping it stretches.

If fibre behaviour is the part you are least sure about, the guide to the best fabrics for hot, humid weather explains how each fibre handles moisture and stretch in daily wear — useful background before you commit to a size you cannot see in person.

Size up or down: the quick decision table

Read it top to bottom with your own measurements in hand and the decision takes under a minute. The full letter-to-centimetre conversion is in the US/UK/EU size guide for Singapore and Malaysia.

What if you choose wrong anyway?

Two safety nets make the between-sizes gamble cheap. First, shipping: orders over $80 ship free to Singapore and Malaysia, which makes adding both candidate sizes to one order — the classic "buy two, keep one" move — a realistic strategy on a $30–50 knit top. Second, returns: every order carries a 30-day return window, so the size you send back costs you a trip to the post box, not the purchase.

The habit that ends the guessing entirely costs nothing: measure once, write the numbers down, and keep them in your phone. Bust, waist, and the shoulder-to-hem length you like. With those three numbers, every "between sizes" moment on the RUIJIN collection becomes a thirty-second check instead of a coin flip.