34D Bra Size Guide

What is a 34D bra?

A 34D bra size combines two key measurements that work together to create your perfect fit. The "34" represents your band size (the measurement around your ribcage), while the "D" indicates your cup size (the difference between your bust and band measurements).

While it’s common for people to over-identify with a certain bra size, the reality is that your cup size is just as much based on your band size as it is your bust size. That means that as your body fluctuates, either monthly or over the course of your life, your cup size can fluctuate too. You may also be different cup sizes from brand to brand as bra sizing can vary across different companies.

Proper bra fit for a 34D bra

Great fit

• The band of the bra is level all the way around your body

• Your breasts fill the cup without spilling over

• The straps should stay on your shoulders without digging in

• The center of the bra lays flat against your chest between your breasts

Too big

• Your breasts don’t fill the cups

• You don’t feel secure or supported

• Your straps fall off your shoulders

Too small

• Your breasts spill out over the cups

• You can feel underwire pinching your skin

• You see red marks on your skin after you take your bra off

What Does 34D Mean?

The band size "34" refers to the measurement around your ribcage directly under your bust. This number forms the foundation of your bra's support structure and should feel snug but comfortable.

The cup size "D" indicates there's a 4-inch difference between your bust measurement at its fullest point and your underbust measurement. Cup sizes follow alphabetical progression (A, B, C, D, DD, etc.), with each letter representing a one-inch increase in this difference.

How to Know if You're a 34D

Finding your true size means taking accurate measurements with a soft measuring tape. It's pretty simple and takes just a few minutes.

For band size, measure directly underneath your bust, keeping the tape parallel to the ground. For cup size, measure around the fullest part of your bust while wearing a non-padded bra. Input each of these measurements into our bra size calculator to get your bra size.

You might be a 34D if your current 36C feels loose in the band, your 32DD feels too tight around your ribs, or your 34C creates spillage at the top or sides of the cups. Keep in mind that breast shape affects fit as much as size. Two people with identical measurements might need different styles to feel comfortable.

Sister Sizes and When to Use Them

Sister sizes share similar cup volume but distribute it differently across band sizes. For a 34D, your sister sizes are 32DD (smaller band, larger cup) and 36C (larger band, smaller cup).

These alternatives come in handy when your standard size doesn't feel quite right. A 32DD offers more support through a snugger band, which is great if you find 34 bands stretch out quickly or if you like firmer support. A 36C gives more breathing room in the band while maintaining similar cup volume. This is perfect for comfort on bloated days or if you're between sizes.

Sister sizes also help navigate differences between brands. Some manufacturers run small or large, making sister sizing helpful for finding your perfect fit across different labels.

You might want to keep multiple sister sizes in your collection to handle natural body fluctuations throughout your cycle or for different activities. For example, you might reach for a tighter band for high-impact movement, or looser bands for lounging.

Best Bra Styles for 34D

When it comes to choosing the right 34D bra, fit is everything. Use our bra size calculator to find your perfect bra fit with just a click. Next, you’ll need to decide if you prefer an adjustable bra style or a hardware-free, pull-over bra style. 

CrossOver Bra

Mesh details add a signature touch to this best-selling, wireless bra. Adjustable straps and a hook and eye closure let you customize your fit. Because the CrossOver Bra is adjustable, it’s a great match for a 34D bra size, which has a relatively small band size and relatively large cup volume. Adjusting your size helps you ensure both the cups and band fit correctly on the body.

Silhouette Bra

Flat, stretch silicone is coated in soft velvetine flocking to provide structure and style to this wireless bra. Adjustable straps and a hook and eye closure let you customize your fit. Once again, this bra’s adjustability and stretchy cups are a great match for a 34D bra size.

SoftForm Bra

The SoftForm Bra is the ultimate wireless smoothing bra. Made with wide, thick straps that lay gently against the skin and a seam-free design that disappears under clothing, this bra is the go-to for comfort and support. The bra’s supportive straps and full coverage cut make this style an excellent match for a 34D bra size, as these features are designed to support a heavier chest.

CloudEmbrace Bra

This cup and band style bra features molded memory foam cups that lift and shape like a traditional t-shirt bra. CloudFuse honeycomb bonding on the wings provides back and side smoothing. Adjust the straps and band for a perfect fit. A 34D bra size will enjoy this style because of its cup and band sizing, which is tailor-made to each specific bra size.

Ready to find your perfect-fitting bras? We design each style with real bodies in mind, using innovative construction that supports without underwire. Whether you need a 34D or want to explore your sister sizes, we're here to help you feel comfortable all day long.