Understanding 40B Bra Size
A 40B bra size is considered a medium band size with a moderate cup size. This size is perfect for people with an average frame and moderate breast volume. Let's explore what makes this size unique and how to find the perfect fit.
Is 40B considered big or small?
Fast facts about 40B
- Snug 40 band with a 2-inch cup jump.
- Standing bust around 41.5–42.5 in keeps the cup filled.
- Share cup volume with 38C, 42A for band tweaks.
- Always scoop-and-swoop and check the gore for a flat anchor.
How 40B is measured
Band fit
Aim for a snug 38.5–39.5 in underbust so the 40 band stays level without digging.
Cup depth
Standing bust in the 41.5–42.5 in range keeps roughly a 2-inch cup difference.
Support focus
Choose firm wings, fully adjustable straps, and swap sister sizes if the band shifts during wear.
40B bust size in inches
| Measurement | Typical inches | How to capture it |
|---|---|---|
| Snug band (ribcage) | 38.5–39.5 in | Measure firmly under the bust on an exhale, then round to the band label. |
| Standing bust | 41.5–42.5 in | Keep the tape level across the fullest point while standing tall. |
| Band-to-bust difference | ≈2 in | Subtract your snug band from the standing bust to confirm cup depth. |
| Approx. cup depth | 3.5–4.5 in | Measure from the underwire root to the apex on a well-fitting bra. |
40B bust size in centimeters
| Measurement | Typical cm | How to capture it |
|---|---|---|
| Snug band (ribcage) | 97.8–100.3 cm | Measure firmly beneath the bust, then map it to EU/FR/JP band labels. |
| Standing bust | 105.4–108 cm | Keep the tape level across the fullest point without compressing tissue. |
| Band-to-bust difference | ≈5.1 cm | Use the difference to double-check your metric cup depth. |
| Approx. cup depth | 8.9–11.4 cm | Trace from underbust to apex on a supportive bra to check projection. |
- Falls inside the 32-36 band range most people wear, giving a familiar fit baseline.
- Close to the statistical average, so it rarely stands out as especially large or small.
- Monitor posture and band tension—small shifts change how the size looks.
- Try sister sizes 38C, 42A to fine-tune band tension.
Quick reference for 40B
- 40B ≈ band 40 label with a 2-inch cup step.
- Projected bust lands around 41.5–42.5 in.
- Use the calculator to convert this size across US/UK/EU/JP systems.
Ranges are approximations—double-check your own measurements for precision.
40B across popular sizing systems
Match US 40B to the most searched regional labels without leaving this guide.
Currently showing the United States (US) label — copy 40B to match tags instantly.
United States (US)
40B
United Kingdom (UK)
40B
Europe (EU)
90B
France (FR)
105B
Japan (JP)
95B
Australia (AU)
18B
Quick converter
Switch systems and copy the exact label for checkout forms or bra tags.
Need step-by-step help? Jump into the dedicated guides below for measurement nuances and shopping tips.
Perfect For
- Average frames
- Medium ribcages
- Moderate breast volume
- Balanced proportions
Recommended Styles
T-Shirt Bras
Perfect for everyday wear under fitted clothing
- Seamless
- Molded cups
- Comfortable
Balconette Bras
Great for creating a natural lift and shape
- Wide-set straps
- Lower cut cups
- Enhancing
Plunge Bras
Ideal for low-cut tops and dresses
- Deep V-neck
- Minimal coverage
- Versatile
How 40B tends to look
40B pairs a 40-band with a 2-inch cup jump, so the silhouette changes with your frame and bra style.
- Keep 38C, 42A in mind—they share cup volume while tweaking the band.
- Shape, strap placement, and fabric choice all influence whether the size looks subtle or bold.
40B compared with nearby sizes
Quick reference when you’re deciding whether to change the band, the cup, or both.
- 40A is one cup shallower—switch when 40B wrinkles along the neckline.
- 40C adds depth while keeping the band snug if you spill out of 40B.
- 38C / 42A keep the same cup volume but tweak band tightness for comfort.
Sister size playbook
- Try 38C when you need tighter or looser band support.
- Try 42A when you need tighter or looser band support.
Fit checks before you buy
When trying on 40B bras, look for these key fit indicators:
- The band should fit snugly around your ribcage
- Cups should fully contain your breasts without spillage
- Straps should stay in place without digging in
- The center gore should lie flat against your chest
- Keep the band parallel to the floor on the middle hook.
- Scoop and swoop tissue into the cups before checking the gore.
- Adjust straps for lift, then reassess comfort after an hour of wear.
Remember that fit can vary between brands and styles. Always try on bras before purchasing to ensure the perfect fit.
Common 40B questions
What size is 40B in other systems?
40B converts to 40B in UK sizes, 90B in EU, 105B in FR, 95B in JP, and 18B in AU.
What does 40B mean?
40B pairs a 40 band with a cup that is roughly 2 inches deeper than the band measurement.
Which sister sizes match 40B?
40B shares cup volume with 38C, 42A. Use them to tighten or relax the band.
How can I confirm this is my best fit?
Measure snug and standing bust, check for smooth cup edges, and ensure the band stays level after a few minutes of wear.
Check 40B with our tools
Measure with the calculator, compare sister sizes, and review the perception guide for styling tips.