Oasis Sizing Guide: Does It Run Big? A Stylist's Complete Guide

Oasis generally runs slightly small, particularly in fitted dresses, tops, and structured pieces—you'll often need to size up compared to other high street brands. As someone who's spent fifteen years styling women of all shapes and sizes, I've seen countless clients frustrated by inconsistent sizing, especially with Oasis. Let me share everything you need to know about navigating their sizing successfully.

The Truth About Oasis Sizing

After analysing thousands of fit reports and working with clients who regularly shop Oasis, here's what I've discovered: their sizing is actually more consistent with traditional UK high street measurements than many fast fashion competitors. However, this means they haven't embraced the vanity sizing that brands like Next and M&S have adopted over the years.

Where Oasis particularly runs small is in their more structured pieces. I always advise clients to size up when buying bodycon dresses, tailored blazers, or anything in satin fabric. The brand's design philosophy seems to favour a closer fit, which works beautifully if you know to compensate for it.

When to Size Up in Oasis

Fitted and Structured Pieces

You'll almost certainly need to go up one size in:

Bodycon or pencil dresses
Tailored blazers and work jackets
Satin or silk-effect pieces
Anything with minimal stretch
Jumpsuits (particularly if you're tall or long-torsoed)

Where Sizing Runs More Generous

Oasis tends to be true to size or even slightly generous in:

Casual jersey tops and t-shirts
Relaxed-fit dresses
Knitwear and jumpers
Flowing midi and maxi dresses

How Oasis Compares to Other High Street Brands

In my experience, Oasis sits somewhere between the vanity sizing of Zara and the more traditional sizing of COS. If you're usually a size 12 in H&M, you might find yourself needing a 14 in Oasis structured pieces, but a 12 works fine in their casual wear.

Mango and Whistles have similar sizing philosophies to Oasis, whilst ASOS tends to run larger across the board. I find Reiss actually runs smaller than Oasis in tailored pieces, making Oasis a good middle ground for professional wear.

My Stylist's Shopping Strategy for Oasis

High Street Alternatives to Consider

When Oasis sizing doesn't work for a client, I often recommend these alternatives:

Jigsaw - Excellent for professional pieces with more forgiving cuts and premium fabrics that work better for curvier figures.

Phase Eight - Specialises in occasion wear with sophisticated sizing that accommodates different body types beautifully.

Premium Options

For clients who love Oasis's aesthetic but want better sizing consistency, I recommend:

Me&Em - Offers similar contemporary styles with more thoughtful sizing and premium fabrics. Their size 12 genuinely fits like a 12 across all styles.

LK Bennett - Perfect for workwear with consistent, flattering cuts that work across different body types.

Luxury Designer Alternatives

For special occasions or investment pieces:

Max Mara - The gold standard for contemporary professional dressing, with impeccable sizing consistency and timeless appeal.

Theory - A cult favourite among stylists for pieces that fit beautifully and translate seamlessly from office to evening.

Independent Brands Worth Discovering

Two brands I've recently discovered that offer excellent sizing and unique design:

Sister Jane - A London-based brand creating vintage-inspired pieces with modern fits. Their sizing runs true and they offer detailed measurements for each piece.

Never Fully Dressed - Known for their Instagram-worthy prints and consistent sizing that actually works in real life, not just for photos.

My Professional Sizing Tips

Always check the fabric content before ordering from Oasis. Pieces with elastane or modal tend to be more forgiving, whilst 100% cotton or polyester items usually require sizing up.

Pay attention to the model's measurements in product photos. Oasis has improved their online imagery, and if a size 8 model looks snug in a dress, you'll definitely want to size up.

For work pieces, I always recommend going up a size. There's nothing worse than a blazer that pulls across the back or a dress that restricts movement during important meetings.

Take the Guesswork Out of Sizing Forever

Honestly, after years of helping clients navigate confusing sizing, I wish tellar.co.uk had existed when I started my career. This ingenious tool has revolutionised how I approach sizing for my clients.

Here's how Tellar works its magic:

Measure once - Simply input your bust, waist, and hip measurements, or use your existing size from a brand that fits you perfectly.
Get instant matches - Use their tellar.co.uk, need guidance from their tellar.co.uk, their fashion hub has you covered.
For comprehensive sizing guidance across all brands, don't miss their tellar.co.uk now and never second-guess your size again. Your wardrobe (and your confidence) will thank you.
Final Thoughts
Oasis remains one of my go-to recommendations for clients seeking contemporary, affordable pieces with a grown-up edge. Yes, their sizing can be tricky, but once you understand their fitting philosophy - size up for structured pieces, stay true for casual wear - you'll find some genuinely beautiful pieces.
The key is knowing your measurements and understanding how different brands interpret sizing. With tools like Tellar taking the guesswork out of online shopping, there's never been a better time to expand your shopping horizons beyond the familiar.