18K
18K Bra Size – Support Where It Counts
Understanding the 18K Bra Size
Finding the right bra size isn't just about a number and letter. It’s about feeling supported, confident, and totally you. The 18K bra size is designed for women with a band size of approximately 18 (AU sizing) and a full, projected cup size of K. In simple terms, that’s a larger underbust (body size) with a high-volume cup – and yes, that support does exist when you shop smart.
Australian bra sizes are based on centimetres, offering precision and consistency in both fit and comfort. What sets The Foundation apart is that we specialise in sizes most retailers simply don’t stock. The 18K is a rare find in traditional stores, but here it’s part of our commitment to inclusive, body-positive support. If you’ve struggled to find your perfect size, this is where your search ends.
International Bra Size Chart
If you’re browsing internationally or have previous bras from other countries, here’s how 18K compares. This is especially helpful for Australian shoppers who purchase from global brands or want to compare sizing with overseas labels.| Region | Size Equivalent |
|---|---|
| Australia | 18K |
| UK | 40K |
| US | 40O |
| EU | 90O |
| France | 105O |
How to Measure Your Bra Size
Grab a soft tape measure and follow this simple bra fit guide::
- Band size: Measure snugly around your ribcage, directly under the bust. This is your underbust measurement. Round to the nearest even number.
- Bust measurement: Measure around the fullest part of your bust.
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Cup size: Subtract the band measurement from the bust measurement to determine the cup.
For more details, visit our size charts.
Sister Sizes & Fit Flexibility
If 18K is hard to find, sister sizes may help. Sister sizes have the same cup volume but slightly different band sizes. For 18K, consider:
- 16L – Tighter band, same cup volume
-
20JJ – Looser band, same cup volume
Just be sure to prioritise band fit first – it’s what provides most of the support. If you need expert help, we're just a message away. You can also visit our detailed sister size guide to learn more about fit options and adjustments
Best Bra Styles for 18K
At The Foundation, we recommend the following bra types for women needing an 18K:
- Wireless bra: Support and comfort without the wire
- Support Wirefree Bralette: Comfortable and functional
- Mesh Comfort Wirefree Bralete: Breathable, seamless, stylish
- Full cup bras: For secure, full coverage
- Side support bras: Centralise and lift
- Sports bras: Especially high impact and low impact options for your activity level
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Strapless bras: With 3-hook closure, wide band, and upright underwire
Look out for comfort features like 24mm wide straps and shaping that accommodates breast tissue comfortably.
Brands That Stock 18K
At The Foundation, we proudly carry 18K styles in these trusted labels:
- Elomi: Plus-size champions known for superior fit
- Prima Donna: For elevated elegance and expert structure
We occasionally feature options from Rose & Thorne and Nala Bras too, although availability may vary. Check back often or sign up for notifications to stay updated on restocks and new arrivals.
Every bra is chosen for its support needs, material quality, and smart product design. Read our returns policy and Customer Reviews for full confidence.
Limited stock available – Shop Now and experience the difference of The Foundation.
Why Shop With Us?
We’re more than just a store — we offer personalised customer service, guided fittings, and a friendly customer service team that’s here to support you every step of the way. Experience sizes across brands with ease and confidence.
FAQs
How do I know if 18K is the right size for me?
Use a tape measure and our Bra Fit Guide, or book a virtual fitting with our expert team.
Are 18K bras easy to find in-store?
They’re rare elsewhere, but The Foundation proudly offers a wide selection including sports bras, nursing bras, and strapless bras.
Can I wear wireless bras in 18K?
Definitely. We stock supportive bralettes and wireless bras perfect for larger breasts.
Do Elomi and Prima Donna bras fit true to size?
Yes, though every body is different. Use our bra finder quiz or chat with our fitters to be sure.
Can I return a bra if it doesn’t fit?
Yes! As long as it meets our return policy, we’re happy to help you find your perfect match.