Possum merino brands from New Zealand don't follow a universal sizing standard. Koru and Trilogy share a sizing system and tend to run true to size. McDonald uses international conversions and fits similarly to Country Road or Icebreaker. Royal Merino runs more generously than the others. None of them map perfectly to, say, what you'd pick up at Zara.
This guide puts our brands alongside labels most of us already own — Zara, Country Road, Icebreaker, R.M. Williams, J.Crew — so you can orient yourself quickly. It's not a replacement for our sizing guide, which has the full body measurement charts; think of it as the shortcut that gets you to the right starting point. Individual product pages also include garment measurements where available, which is the most reliable comparison of all.
All comparisons below are for garments: jumpers, cardigans, jackets, and coats. For accessories like gloves, beanies, and socks, you'll find measurements on each product page.
How Sizing Works Across Our Brands
Koru and Trilogy are made at the same Warkworth mill and use identical sizing — if you know your size in one, you know it in the other. Their sizing is based on body measurements (bust and chest), running from XS/8 through to XXL/18 for women, and S through 3XL for men. Both brands offer a range of fits across their range, from close-fitting zip jackets designed to sit precisely at the shoulder through to relaxed-cut jumpers with generous ease through the body. The product images are the best guide to how fitted a particular style is intended to be.
McDonald uses international size conversions rather than body measurements. Their charts cover AU/NZ, UK, US, Italian, French/EU, and Japanese sizing, so wherever you usually shop, there's a reference point. The full conversion table is on our size guide page.
Royal Merino's women's range sizes more generously than the other three brands. Their women's XS starts at 87cm bust compared to Koru's 82–85cm — roughly half a size larger at each point. Royal Merino provides both size conversions and body measurements for women, which makes comparison straightforward. Their men's range uses the same international conversion system as McDonald.
Women's Sizing: How the Brands Compare
The table below maps each brand's women's sizing against familiar reference points. All figures are bust measurements in centimetres.
| Brand | XS / 8 | S / 10 | M / 12 | L / 14 | XL / 16 |
|---|---|---|---|---|---|
| Koru & Trilogy | 82–85cm | 86–89cm | 90–93cm | 94–97cm | 98–101cm |
| Royal Merino | 87cm | 92cm | 98cm | 104cm | 110cm |
| Zara | 84cm | 88cm | 92–96cm | 100cm | 104cm |
| Country Road | 85cm | 90cm | 95cm | 100cm | 105cm |
| Icebreaker | 76–82cm | 82–88cm | 88–94cm | 94–100cm | 100–107cm |
Koru and Trilogy sit very close to Zara and Country Road — a reliable S in either of those is almost certainly an S/10 in Koru. Icebreaker runs slightly smaller across the board, designed for a close-to-body merino base layer fit; if you wear a M in Icebreaker, an S/10 or M/12 in Koru will likely suit a mid-layer wear pattern better. Royal Merino is the most generous of our brands — their M at 98cm bust sits between what Koru calls M/12 (90–93cm) and L/14 (94–97cm), so many women find they size down one step from their usual.
McDonald doesn't publish body measurements, but their AU/NZ size conversions follow standard conventions: XS is an AU/NZ 8, S is a 10, M is a 12, and so on through to 2XL at AU/NZ 18. If you know your AU/NZ or UK dress size, McDonald is the most straightforward of the four to navigate.
Men's Sizing: How the Brands Compare
Men's sizing across Koru, Trilogy, McDonald, and Royal Merino is more consistent than the women's range. The table below uses chest measurements in centimetres for Koru, Trilogy, R.M. Williams, and Icebreaker. McDonald and Royal Merino both use size labels (XS–3XL) with full regional conversions — including US, UK, Italian, and French/EU — on our size guide page.
| Brand | S | M | L | XL | XXL |
|---|---|---|---|---|---|
| Koru & Trilogy | 92cm | 97cm | 102cm | 107cm | 112cm |
| McDonald & Royal Merino | XS | S | M | L | XL |
| R.M. Williams | ~92cm | ~97cm | ~102cm | ~107cm | ~112cm |
| Icebreaker | 84–91cm | 92–99cm | 100–107cm | 108–115cm | 116–124cm |
Koru and Trilogy are essentially true to AU/NZ sizing and closely match R.M. Williams, which is also widely considered true to size. If your R.M. Williams shirts and merino layers fit well, the same size in Koru will work. Icebreaker men's sizing starts lower than Koru's at the S end — if you're at the upper end of Icebreaker S (around 91cm chest), Koru S at 92cm is the natural next step and will sit with more ease, which suits the way these heavier knitwear pieces are worn.
For US Shoppers
AU/NZ sizing runs about two numeric sizes above US sizing for women — a US 4 is an AU/NZ 8, a US 6 is an AU/NZ 10, a US 8 is an AU/NZ 12. If you typically wear a S in J.Crew or Banana Republic (US 4–6), you're most likely an XS/8 or S/10 in Koru and Trilogy. A US M (8–10) maps to roughly S/10 or M/12 in our sizing.
McDonald's and Royal Merino's men's charts include explicit US size conversions — Royal Merino's men's US sizing runs 34–46 (chest in inches), making it one of the clearest references for US men shopping our range. McDonald follows the same system. Full conversion tables for both brands are on our size guide page.
McDonald's women's charts also include explicit US size conversions, so their size guide is the clearest reference if you shop primarily in US sizes — a US 4 is their XS, US 6 is S, and so on through to US 14 at 2XL.
It's worth noting that Uniqlo, which many US shoppers use as a sizing reference, runs noticeably slim — particularly in the shoulder and upper arm. If Uniqlo is your usual benchmark, you'll likely find our brands have considerably more ease at the same label size, which is intentional for the layered, cold-weather wear these garments are designed for.
Fit Style and Layering
Possum merino knitwear has natural stretch — the fibres move with you — but less elastic recovery than synthetic blends. It won't spring back to shape the way a performance fabric does, which means sizing decisions matter more than with everyday knitwear. A garment that's slightly too small will feel tight and stay tight; one that fits well will ease comfortably with wear.
The most important thing to consider is how fitted the particular garment is designed to be. A close-fitting zip jacket — the kind where the shoulder seam sits precisely at the edge of your shoulder — should be sized for your body, not your layers. Sizing up on a structured piece like this shifts the shoulder seam off position and changes how the sleeves hang. Size for fit first; the garment will do its thermal job regardless.
Relaxed and classic-cut jumpers are a different story. A thin merino sweater or base layer underneath won't require a size change — there's already enough ease built in. If you're planning to layer something bulkier, or if you naturally run between sizes, going up one is the right call.
The product images are the most reliable guide to fit style. A garment sitting close to the body on the model, with visible shape through the torso and arms, is cut to fit — size for your body measurements. A looser drape through the body signals more room to work with.
Not sure? Get in touch — we're happy to help you find the right size before you order. Full body measurement charts for all four brands are on our size guide page. For Koru and Trilogy, individual product pages also include garment measurements — comparing those flat against a jumper or jacket that already fits you well is the most reliable method of all.
