What Is Sizing Like at Sweaty Betty?

By Ella Blake — Fashion Stylist | Tellar Fashion Hub — Always honest, unbiased & unsponsored

Sweaty Betty runs true to UK size across most of its range, but there are some important garment-specific differences — particularly with leggings and sports bras — that are genuinely worth knowing before you order.

I'll be honest — I was late to the Sweaty Betty party. For years I dismissed it as a bit too premium for gym kit, the sort of thing you bought to look like you were serious about fitness rather than actually being serious about it. Then a client of mine basically strong-armed me into trying a pair of their Power Leggings, and I completely ate my words. They are, without a doubt, some of the best-fitting leggings I have ever worn — and I have tried a lot of leggings in the name of professional research. The waistband doesn't roll, the fabric holds everything in without feeling like a compression bandage, and they still look good enough that I've worn them to the coffee shop after a class without feeling like I've made a terrible lifestyle decision. Converted. Completely.

The brand was founded in London back in 1998 and has built a seriously loyal following — not just among gym-goers but among women who simply want activewear that performs and looks brilliant doing it. It's a British brand through and through, and the sizing reflects that.

The Size Range

Sweaty Betty offers sizes XS through to 3XL, which roughly translates to a UK 6 through to a UK 22. That's a solid range and far better than many premium activewear brands manage. Here's the full size conversion breakdown:

Sweaty Betty SizeUK SizeEU SizeUS SizeBust (cm)Waist (cm)Hips (cm)XS6–834–362–480–8562–6787–92S8–1036–384–685–9067–7292–97M12–1440–428–1090–9672–7897–103L14–1642–4410–1296–10278–84103–109XL16–1844–4612–14102–10884–90109–1152XL18–2046–4814–16108–11490–96115–1213XL20–2248–5016–18114–12096–102121–127

Note that Sweaty Betty uses a banded sizing system (XS to 3XL) rather than numbered UK sizes, and each size covers a two-size span. If you're right on the boundary — say a true UK 10 — it's worth reading the garment-specific notes below before deciding whether to size up or down.

Sizing by Garment Type

This is really where the detail matters. "True to size" means something different depending on what you're buying:

Power Leggings: The brand's hero product and, in my experience, the most reliable fit. They are designed to be close-fitting and sculpting, so they will feel snug when you first put them on — that's intentional, not a sizing error. Stick to your usual size. If you're between sizes and prioritise comfort over compression, go up.
Zero Gravity Leggings: A slightly more relaxed, lightweight fit compared to the Power range. True to size and a better option if you find the Power leggings too firm through the thigh. These are my recommendation for running and high-impact cardio.
Bum-sculpting & contour styles: These are designed with strategic seaming to lift and shape, so they do run on the firmer side. I'd advise going true to size — sizing up actually defeats the purpose of the construction. Trust the size.
Sports bras: This is the one area where I'd tell you to size down, particularly if you're between sizes. Sweaty Betty's sports bras are engineered for support and they need a close, firm fit to do their job properly. If you're a 34B/C, for example, and sitting on the boundary of S and M, go with the S.
Shorts: Generally true to size. The cycling-style shorts in particular fit brilliantly and don't ride up — a point worth noting, because shorts that don't ride up are genuinely worth celebrating.
Tops, long sleeves & jackets: True to size and often a touch generous through the body, which makes them very wearable for layering or casual wear beyond the gym. No surprises here.
Swimwear: Sweaty Betty's swimwear runs slightly smaller than their activewear, particularly through the bust. I'd recommend sizing up by one if you're fuller-busted, and always checking the specific measurements rather than going purely on your usual activewear size.

What About Tall & Petite Fits?

Sweaty Betty doesn't offer a formal petite or tall range, which is genuinely a gap in what is otherwise a well-considered brand. The leggings are cut for a standard inseam of roughly 28 inches — fine for most, but if you're 5'9" or taller, you may find the full-length styles fall slightly above the ankle. Petite women, on the other hand, will likely find them more of a cropped length, which can actually look brilliant with trainers and a hoodie if you lean into it.

Fabric & Fit Technology

One of the reasons Sweaty Betty sizing behaves differently to regular fashion is because of the fabric technology involved. Many of their fabrics — particularly the signature Power fabric — are designed to compress and sculpt, which means they feel tighter in the hand than they do on the body. Don't be alarmed when you pull them out of the bag. The stretch recovery on most of their key fabrics is excellent, which is why they hold their shape wash after wash.

A client of mine once returned a pair because she was convinced they were a size too small — I made her put them on before sending them back and, predictably, they fit perfectly. It's one of those cases where you really do have to put them on your body and not trust your first impression from the hanger.

Similar Brands to Consider

Sweaty Betty sits in the premium activewear space — genuinely quality kit, priced to reflect it. Here's where to look across different budgets and styles:

High Street & Mid-Market Options:

Lululemon — The closest direct competitor in terms of quality and price positioning. Their Align leggings are the SB Power Leggings' main rival. Sizing runs slightly more generously than Sweaty Betty.
Gymshark — The UK's homegrown activewear success story. More affordable than Sweaty Betty, strong on seamless sets and training gear. Sizes tend to run small so check the guide carefully.
ASOS — Their own-brand activewear line offers solid basics at a much lower price point. Good for trying out different silhouettes before investing in premium.
H&M — The Move range is vastly underrated. The high-waist leggings in particular are excellent value and true to size.
Abercrombie & Fitch — Their YPB (Your Personal Best) activewear line has quietly become one of the better options at the mid-market level. Flattering cuts and reliable sizing.
Urban Outfitters — Carries a curated mix of independent and own-brand activewear. Good for trend-led pieces and colourful sets if the Sweaty Betty palette feels a touch conservative.
New Look — Budget-friendly activewear basics done well. Not a like-for-like comparison in terms of fabric tech, but perfectly decent for low-impact workouts and everyday wear.

Premium Options:

Varley — A California-born, London-loved activewear brand that bridges the gap between gym and lifestyle beautifully. Similar price point to Sweaty Betty with a slightly more laid-back aesthetic. Sizing is very consistent.
Adidas by Stella McCartney — If you want genuine performance credentials combined with designer credibility, this collaboration delivers. Runs true to size.

Independent Picks (my off-piste recommendations):

Tala — A brilliant British independent brand founded by Grace Beverley that is doing everything right: sustainable fabrics, size-inclusive (XXS–4XL), and genuinely well-constructed. The leggings hold up against Sweaty Betty at a significantly lower price. If you haven't tried them, you should.
Girlfriend Collective — An independent American brand with a strong UK following, particularly celebrated for its size range (XXS–6XL) and its use of recycled materials. The Compressive leggings are a direct rival to the SB Power Leggings and — I'll say it — possibly more comfortable. Sizing is true to size and very clearly laid out on their site.

Stop Guessing Your Size — Use Tellar

Activewear sizing is genuinely tricky — brands use different fabric tensions, compression levels, and size spans, so your usual number doesn't always translate cleanly. That's exactly why I point everyone to Tellar.co.uk — the UK's leading free sizing tool, matching your measurements to 1,500+ brands instantly.

✔ Enter your measurements once — bust, waist, hips, or an existing brand size
✔ Get your precise size across Sweaty Betty, Lululemon, Gymshark, and 1,500+ more
✔ Use the Store Size Lookup tool for instant brand-specific sizing
✔ Always free. Works in-browser. No app, no account needed.

Tellar is completely independent — no brand sponsorships, no affiliate influence on the data. Just accurate sizing matched to your body. It's the tool I wish I'd had on day one of my styling career.

Find Your Sweaty Betty Size →