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Tips Before You Get Started

Wear a non-padded, unlined bra Padded or push-up styles add volume that throws off your numbers. A soft, unlined bra gives you the most accurate baseline.
Grab a soft measuring tape A flexible fabric or plastic tape is essential. No tape? A piece of string and a ruler works just as well.
Stand straight with your arms relaxed Your posture affects your measurements more than you'd think. Stand naturally — no holding your breath, no slouching.
Check the tape is level all the way around Use a mirror, or ask someone to help. Even a slight dip at the back can shift your measurement by a full size.

How to Use The Size Chart

Use this sister size chart as a general guide to understand how bra sizes can relate to one another. Sizes listed in the same row usually share a similar cup volume, even though the band size is different. Keep in mind that bra fit can vary by style, fabric, stretch, wire construction, and brand sizing. Your calculated size is a helpful starting point, but the best fit should still feel comfortable through the band, cups, straps, and center front.

For example, if you usually wear a 34C and the cups feel right but the band feels too tight, your sister size may be 36B. If the band feels too loose, you may try 32D instead. A 36D has a similar cup volume to 34DD/E and 38C, while a 40DD/E is close in cup volume to 38DDD/F and 42D. Sister sizing works best when the cup volume feels right, but the band needs a better fit.

How to Measure Your Bra Size Accurately

Before using our bra sizing chart, grab a soft measuring tape and take two quick measurements—this is the key step in how to measure bra size accurately. These measurements help you find your ideal band and cup fit so you can choose a bra that feels truly comfortable and supportive.

1. Measure Your Underbust (Band Size)

Wrap a soft measuring tape around your ribcage, right under your bust where your bra band normally sits. Keep the tape level and snug, but not tight. Then match your underbust measurement to the band chart to find your band size.

2. Measure Your Bust (Cup Volume)

Measure around the fullest part of your bust, keeping the tape relaxed and level. Next, subtract your underbust measurement from your bust measurement. Use that difference in the bust chart, together with your band size from Step 1, to find your estimated bra size.

For example, if your underbust is 31" and your bust is 36.5", your underbust falls in the 30.5–32.5" range, so your band size is 34. The difference is 36.5" - 31" = 5.5", which falls in the 5–6" column. In the bust chart, band size 34 and the 5–6" column give you an estimated size of 34C.

Why You Should Recheck Your Bra Size Regularly

Your body naturally changes over time, and so does your bust. Factors like weight fluctuations, hormonal changes, pregnancy, aging, and lifestyle shifts can all affect your bra fit—even if you’ve been the same size for years.

That’s why it’s important to measure your bra size regularly instead of relying on a once-done fitting. A bra that once fit perfectly may no longer provide the support, comfort, or shape you need today.

Using a bra sizing calculator or sizing chart periodically helps ensure you’re always wearing the right size. A well-fitting bra improves comfort, enhances support, and helps your clothes fit better—no matter what stage of life you’re in.

FAQs

Your straps may be too long or your cup size could be too big.
Tip: If the cups can’t sit snugly against your body, the straps end up doing the holding. Try sizing down the cup or adjusting the strap length.

Your band might be too loose.
Tip: When your straps carry too much weight, it’s usually because the band isn’t providing enough support. Check that your band fits firmly around your ribcage — it should stay in place without digging.

Your band may be too big.
Tip: A band that moves or rides up indicates it’s not tight enough. A properly fitting band should sit horizontally and feel secure, helping your cups stay in the right position.

Your cups may be too large.
Tip: When the fabric isn’t filled out by your breasts, it can fold or wrinkle. Consider a smaller cup size or a style with slightly less coverage to smooth the fit.

Your cups may be too small.
Tip: Even if the sides or top seem fine, if the center gore lifts away from your body, your breasts are pushing it out. Try going up a cup size to ensure proper support and comfort.

Your cup size might be off.
Tip: Poking can happen if the wire is too small to fully support your breast, or if a too-large cup allows the wire to shift. Adjusting your cup size up or down usually resolves the issue.