Bra Sister Sizes Explained
How to Find the Perfect Fit
Did you know that most women wear the wrong bra size? Often, the problem isn’t the cup size but the band size—and that’s where sister sizes come in.
Once you understand how sister sizes work, you can find a fit that feels perfect every day. This guide will help you understand the logic behind sister sizing and find bras that support you, fit well, and feel great.
What does sister size mean?
A sister size is an alternative bra size with the same cup volume but a different band size. In other words, cup size isn’t defined by a letter alone—it always depends on the band size.
For example, 75D and 80C are sister sizes. Although the cup letter changes, the cup volume remains nearly the same. As the band size increases, the cup letter goes down; as the band size decreases, the cup letter goes up.
Sister sizes can help you fine-tune the fit of your bra. If the band feels too tight but the cups fit well, try going up one band size and down one cup letter. If the band feels loose, go down one band size and up one cup letter.
How to Find Your Sister Size in 3 Easy Steps
- Identify your current size. Start with the size that currently feels right.
- Decide whether you need a tighter or looser band.
- Tighter band = smaller band size, larger cup letter (e.g., 80E → 75F).
- Looser band = larger band size, smaller cup letter (e.g., 75D → 80C).
- Try it on and check the fit. The right sister size feels comfortable, stays in place, and provides even support without digging in or gaping.
Examples of Sister Sizes
If you wear a size 80F, your sister sizes are 75G and 85E. If the band on a 75D feels too tight, try 80C. If 80C feels loose, try 75D for firmer support.
The Most Common Sister Sizing Mistakes
Many people make the same mistake: when a bra feels tight, they go up a band size but keep the same cup letter. As a result, the bra no longer provides proper support, and the underwires ride up from beneath the breasts. Another common mistake is focusing only on the cup letter. Although a D cup may sound large, its actual size always depends on the band size. For example, a 70D cup is considerably smaller than an 85D cup. It’s also important to remember that sizing can vary across styles and brands, so it’s normal for your size to differ slightly from one brand to another.
Frequently Asked Questions About Sister Sizes
Find your perfect-fitting bra
Understanding sister sizes is the key to finding your perfect fit. At Meritta Bra, we want to make it easy for you. Explore our collection and find bras that support you, fit well, and feel great every day.
About Us
Meritta Bra has been in business for over 20 years, and we have helped more than 100,000 customers find bras that fit perfectly. We are a Finnish family-owned business with personal service, sustainability, and ethical practices always at the heart of what we do.
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