What Is Sizing Like at SIR?

The short answer

SIR the Label is the Sydney contemporary house known for beautiful linen, sharp tailoring and those shirred, tiered dresses that show up on every Italian-holiday Instagram by June. It's broadly true to size, but it runs on Australian designer numeric sizing rather than UK dress sizes, and that's where almost all the confusion comes from. Once you've translated the numbers, the fit itself is fairly predictable.

Here's the system, in plain English:

SIR 0 ≈ UK 6
SIR 1 ≈ UK 8
SIR 2 ≈ UK 10
SIR 3 ≈ UK 12
SIR 4 ≈ UK 14

So my "size 2" client was an absolutely standard UK 10. No toddler clothing involved. Crisis averted, dress kept, and she's since bought three more.

The fit detail that actually matters

SIR is cut on the slim, polished side — this is elevated, grown-up Australian design, not a relaxed beach throw-on. A few things worth knowing before you commit:

Go by your waist, not your bust. SIR themselves recommend this, and it's good advice. Their pieces are quite waist-defined, so if your measurements fall across two columns (say a bust that says 2 but a waist that says 1), follow the waist for the cleanest line.
The shirred and corset-style tops run snug on purpose. That gathered, ruched bodice you see on so many SIR dresses is meant to sit close — it's "comfortably firm" rather than "size up." Tunnel into them from the bottom hem rather than yanking over your head, or you'll stress the stitching.
Tailoring is true but structured. The blazers and trousers fit close through the shoulder and waist. If you're between sizes or carry a bit more across the bust, the larger number gives you a far more comfortable jacket.
Linen behaves like linen. A lot of SIR's signature pieces are 100% linen, which softens and relaxes slightly with wear. It won't grow dramatically, but a fresh-from-the-bag linen dress can feel a touch crisper than it will after a wash or two.

The petite option nobody talks about

This is the bit I genuinely love and almost no one mentions: SIR offers a "0P" petite size. It's designed for frames under roughly 5'3" (160cm). Cleverly, the body measurements barely change from a standard 0 — only about 2.5cm — but the length is shortened significantly: roughly 7cm off the hem and 5cm off the sleeves.

If you're petite and you've spent years getting SIR dresses taken up at the tailor's, this is the answer. I had a maxi shirt-dress hemmed twice before I clocked that the 0P existed — an expensive lesson I'm passing straight on to you.

Where SIR catches people out

Three honest watch-outs from years of dressing clients in this label:

Final-sale items are unforgiving. SIR sells a lot through sale and final-sale channels, and exchanges on those can be genuinely difficult. If you're buying a final-sale piece, this is the moment to get your size right rather than gambling.
Some occasion pieces run generous. A handful of the looser, swing-cut dresses come up roomy — a couple of my clients have needed to size down on those, which is the opposite of the fitted styles. Check the specific garment measurements, which SIR lists per product.
The delicate fabrics need respect. Ruffles, fine linen and shirring are beautiful but not bombproof. Don't size down hoping a snug fit will "just stretch" — it tends to strain the seams rather than give.

My quick how-to-buy

If you take nothing else away, take this:

Measure your bust, waist and hips properly before ordering — five minutes saves a return.
Translate to the SIR number using the guide above, then let your waist break any ties.
Petite? Look for the 0P before you reach for a tailor.
Buying tailoring or a structured bodice? Size up if you're caught between.
Buying a swingy or oversized cut? Check the garment measurements — you may want to size down.

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If SIR isn't quite the one: where else to shop

SIR sits in that lovely sweet spot between polished minimalism and occasion-ready — Australian contemporary at its best. If you love the look but want options at different price points (or just a bit more size range), here's where I'd send you.

On the high street and accessible end:

Aligne — clean contemporary tailoring and slip dresses with a very SIR-adjacent sensibility, at a friendlier price.
Albaray — grown-up, considered pieces and lovely linen separates for the SIR customer who wants everyday wear.
Massimo Dutti — the place for structured trousers and elevated tailoring that punches well above its price tag.
Reiss — sharp occasion dressing and beautifully cut suiting when you need polished and reliable.

Two independents worth knowing:

ESSE Studios — a quietly brilliant Australian label built on minimal, sculptural tailoring and natural fibres; deeply SIR in spirit but its own thing.
St. Agni — Byron Bay's masters of pared-back, neutral, beautifully made wardrobe staples for anyone who lives in tonal minimalism.

Stepping up to premium:

Aje — the other great Sydney name, big on texture, shirring and statement event pieces if you want drama with your minimalism.
Camilla and Marc — refined Australian tailoring and eveningwear with a slightly more architectural edge than SIR.

And at the luxury / designer level:

Zimmermann — the natural next step up for SIR's romantic, linen-and-lace holiday dressing, with red-carpet polish.
Toteme — Scandinavian minimalism for the SIR customer who has gone fully tonal and wants investment tailoring that lasts decades.

Whichever way you go, the principle is the same: know your real measurements, learn the brand's quirks, and buy with confidence rather than crossed fingers. SIR is a brand absolutely worth getting right — those linen dresses earn their place in a wardrobe for years.