Find your right fit
RBF sizing varies by style. Always check the sizes available on the individual product page before you add to bag.
How RBF sizing works
- Each product lists only the sizes that exist for that style.
- Current catalogue styles may use Free Size or numeric sizes such as 34, 36, 38 and 40 — not every product uses S/M/L or XS–XXL.
- Fit depends on stretch, construction, body shape and comfort preference.
- If you are unsure, use WhatsApp fit help from the product page or Contact.
What sizes does Free Size cover?
Our current Free Size bras generally accommodate band sizes 28–38, bust measurements 32–42 inches, and cup sizes A–C.
| Measurement | Range |
|---|---|
| Usual bra band size | 28–38 |
| Fullest bust measurement | 32–42 inches |
| Cup range | A–C |
Free Size means one flexible size that accommodates a range of measurements. Fit and support vary by style and your combination of band and cup size; it isn’t a guaranteed fit for everyone within these ranges.
Band size is the number in your usual bra size, such as 34 in 34B. Bust measurement is measured around the fullest part of your chest.
Unsure about your fit? Send us your usual bra size and the product link on WhatsApp.
How to measure underbust and bust
You need a soft measuring tape and a mirror. Wear a thin, unpadded bra, or none. Keep the tape level and snug—not painfully tight.
- Underbust (raw measurement) Wrap the tape snugly around your ribcage, directly under your bust. Keep it flat against your back, exhale, and note the measurement in inches or centimetres.
- Bust Stand straight and wrap the tape around the fullest part of your bust. Keep it level all the way around without pressing into the tissue.
Important: a labelled band size on a bra (for example “34”) is not always identical to your raw underbust measurement in inches. Brands convert measurements differently, and cup labels depend on the sizing system and manufacturer. Use product-page sizes as the source of truth for what RBF sells.
Understanding band and cup sizes
- Band (the number on traditional sizing): relates to how the bra sits around the ribcage. Much of the support usually comes from the band when the style is designed that way.
- Cup (the letter): describes the relationship between bust and underbust in a given sizing system. Cup volume is not a fixed absolute—so a 36C holds more than a 32C.
- Many RBF styles use Free Size or numeric options rather than full band/cup grids. Do not assume every product follows wired-bra band/cup charts.
A common educational method subtracts underbust from bust and maps each inch of difference to a cup letter. That method is a starting point only; measurement rules and letter labels vary by system and brand.
Fit checks and sister sizes
Use these checks as comfort guidance. Not every check applies to every construction—for example, centre-gore “sits flat” advice from traditional wired bras does not apply universally to wireless or soft Free Size styles.
- Prefer a secure, comfortable feel — not painfully tight.
- The band or under-bust edge should sit fairly level when the style has a defined band.
- Cups or cups-like panels should hold without uncomfortable spilling or empty gaping for that style.
- Straps should stay in place without digging in.
- Coverage and support should feel appropriate for the product you chose.
Sister sizes (when a style uses band/cup sizing)
Sister sizes keep similar cup volume on a neighbouring band: go up a band and down a cup letter (for example 34B → 36A), or down a band and up a cup (34B → 32C). A sister size will not feel identical—re-check band comfort and coverage. This mainly helps when comparing traditional sizes across brands; Free Size products are still chosen from that product’s own guidance.
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Band rides up at the back
Try a smaller band with a larger cup volume.
-
Straps dig into shoulders
Your band may be doing too little of the work.
-
Gaping at the top of the cup
Try a smaller cup or a different style.
-
Fabric spilling over the edge
Try a larger cup in the same band.
Understanding S/M/L sizing
S, M and L (and similar letter sizes) group a span of body measurements into fewer options. They are a shopping shorthand—not a guarantee that every body in that letter label will get the same fit.
RBF does not publish generic S/M/L conversion tables as confirmed product measurements. If a style uses letter sizing, rely on that product’s size list and any verified fit guidance on its page. Many current RBF styles use Free Size or numeric sizes instead.
Numeric sizes
Some bras are sold in numeric sizes (for example 34, 36, 38, 40). Availability depends on colour and style — not every colour has every size. We do not invent cup, bust or underbust mappings here; use the sizes shown on the product page.
Teen & First Bras
Teen & First Bras focus on everyday comfort, gentle support, breathable or lightweight construction, comfortable straps, appropriate coverage and a non-restrictive fit. Some styles in this collection are Free Size. Exact fit depends on the product — always check the product page.
Fit tips
- Measure over a soft, unpadded bra or bare skin.
- Keep the tape level and snug, not tight.
- Your band should sit horizontally and feel firm.
- Most of the support should come from the band, not the straps.