Does the Brand Onia Run Big or Small? What Is Their Sizing Like & What’s Worth Buying?

Onia is a rising luxury brand offering elevated resortwear and minimalist swim essentials. Known for its clean lines, technical fabrics, and premium tailoring, Onia has become a go-to for men and women who want style and sophistication poolside or on the beach. But before you check out, you might ask: Does Onia run big or small?

📌 Here’s what you need to know first: Tellar.co.uk lets you find your size in thousands of brands—including Onia—with one quick, free setup. You’ll receive a free measuring tape, and we’ve already analysed Onia’s full sizing data. No catches. No guesswork. Just your perfect fit.

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Who Is Onia For?

Founded in New York in 2009, Onia is a modern brand focused on:

• Luxury swimwear and minimalist resort pieces

• Neutral colour palettes and technical fabrics

• Tailored silhouettes in shorts, shirts, and bikinis

• Elevated basics made from linen, stretch cotton and quick-dry blends

While it looks relaxed, Onia’s fit is precise—especially in swim shorts, tailored shirts, and structured bikinis. That makes sizing accuracy crucial.

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So, Does Onia Run Big or Small?

Overall: Onia runs slightly small—especially in swimwear and tailored styles. Resortwear tops and relaxed-fit pieces run true to size.

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For Men:

• Swim shorts: Cut slim in the leg with tailored waistband

• Linen shirts: True to size with a close fit at shoulders

• T-shirts and polos: True to size, modern (not boxy) silhouette

• Fit tip: Size up in swimwear or if you’re muscular or in-between sizes

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For Women:

• Bikinis and one-pieces: Run small—especially cup sizes and waist

• Dresses and skirts: Structured with minimal stretch

• Loungewear and linen shirts: True to size, relaxed fit

• Fit tip: Size up in swimwear and fitted dresses

Need help choosing between a Small or Medium bikini or figuring out your best fit in Onia’s stretch trunks? Use Tellar here for instant, body-matched recommendations.

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Onia’s Size Chart vs UK Sizing

Onia uses US sizing, which can feel slightly small compared to UK high-street sizing—especially in tailored styles.

🎯 Tellar.co.uk auto-converts and adjusts based on your height, waist, hips and chest—essential for a tailored brand like Onia.

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Fabric Fit Guide: What You Need to Know

Onia prioritises premium fabrics with form-fitting cuts. Depending on the collection, stretch and ease may vary.

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🩳 Men’s Swimwear (Stretch Nylon or Linen-Blend)

• Slim at thigh, fixed or drawstring waistband

• Minimal elastic stretch

• Fit tip: Size up if athletic build or in-between waist sizes

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👙 Women’s Swimwear (Lycra-Nylon)

• Minimal coverage, double-lined

• Tight across hips and chest

• Fit tip: Runs small—size up for full coverage or support

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👕 Linen Shirts, Polos & Shorts

• Lightweight and breathable

• Fitted shoulders and waist

• Fit tip: True to size in tops—check hip size in shorts

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🧵 Dresses & Skirts (Structured Cotton or Crepe)

• Clean lines with minimal stretch

• Zipped waistlines or darts

• Fit tip: Size up for comfort in waist/bust if curvy

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Bestselling Onia Pieces & How They Fit

1. Calder 7.5" Swim Trunks

Tailored swim short, stretch lining, classic fit.

➡️ Fit tip: Runs small in seat and thigh—size up if muscular

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2. Elena One-Piece Swimsuit

Scoop back, high-cut leg, clean neckline.

➡️ Fit tip: Runs small—size up in cup and torso if in-between

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3. Jack Linen Shirt

Signature relaxed shirt in premium linen.

➡️ Fit tip: True to size, neat through shoulder

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4. Kelly Bikini Set

Minimalist triangle or bandeau top with high-leg bottom.

➡️ Fit tip: Size up for support, especially in bust

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5. Wide-Leg Resort Trousers (Women)

Lightweight, flattering silhouette, minimal stretch.

➡️ Fit tip: True to size at waist—use Tellar for hip fit

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Onia vs Other Luxury Resortwear Brands

🧠 Compare all these brands in one click with Tellar’s fit matching engine.

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Common Fit Complaints (And How Tellar Fixes Them)

❌ “The swimsuit looked amazing but didn’t cover anything.”

Tellar factors in your bust, torso and hip ratio to recommend a size and style.

❌ “I bought my usual M trunks and they were too tight to move in.”

Tellar compares waist and thigh width to real product specs—no guesswork.

❌ “Shirt fit well in the shoulders but not at the waist.”

Tellar personalises the recommendation based on your build—not just labels.

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Why Use Tellar Before Buying Onia?

Onia offers clean, minimalist pieces—but the fit is tailored and unforgiving. Tellar.co.uk ensures you don’t waste money on the wrong size.

• ✅ Match your chest, waist, hips, and height to exact Onia sizes

• ✅ Get a free soft tape measure posted to your door

• ✅ Find your size in thousands of brands as your wardrobe evolves

• ✅ Skip returns and exchanges—know your fit before checkout

• ✅ 100% free—no upsells, no accounts required

🎯 Create your Tellar profile now

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Related Tellar Sizing Guides

• Orlebar Brown Sizing Guide

• Reiss vs Onia Fit Breakdown

• Does Skims Swim Run Small?

• Massimo Dutti Fit Explained

• How to Measure Yourself for Swimwear

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Follow Tellar for Swimwear & Resortwear Fit Insights

• 📍 Instagram @Tellarsizing

• 📍 Twitter (X) @TellarSizing

• 📍 Pinterest

• 📍 Facebook Page

We post weekly sizing guides, fit tips for luxury resortwear, and seasonal size updates.

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Final Thoughts: Onia Runs Slim—But Tellar Gets the Fit Right

Onia is sleek, premium and made to flatter—but it doesn’t leave much wiggle room. Whether you’re shopping for a holiday, honeymoon, or elevated basics, the fit is key to making it work.

Tellar.co.uk helps you get it right the first time. We’ve analysed Onia’s product data and compared it to real-world bodies—so you can shop with confidence.

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“Find your size in thousands of brands. It’s free & easy.”

🎯 Use Tellar Now