The main difference is in how band size is calculated. UK sizing uses your actual underbust measurement rounded to the nearest even number, while US sizing adds 4-5 inches to your underbust. For example, a 32-inch underbust would be a size 32 band in UK sizing, but a 36 or 37 band in US sizing. The UK method is generally considered more accurate for modern elastic bras, providing better support with a snugger band fit.

You should recalculate your bra size every 6-12 months as a routine check, or immediately after significant body changes like weight fluctuation of 10+ pounds, pregnancy, breastfeeding, starting or stopping hormonal birth control, or menopause. Your bra size can also change due to aging, muscle gain, or hormonal cycles. If your current bras feel uncomfortable, ride up, or leave marks, it's time to remeasure.

Sister sizes are alternative bra sizes with the same cup volume but different band sizes. When you go down one band size, you go up one cup size (and vice versa). For example, 34C, 32D, and 36B are all sister sizes with the same cup volume. Use sister sizes when your exact size is unavailable, when you want a tighter or looser band, or when trying different bra styles that fit differently. They're also helpful when switching between brands with varying sizing standards.

Bra sizing isn't standardized across brands, similar to clothing sizes. Different manufacturers use different sizing methodologies, fabric stretch, cup shapes, and quality control standards. Victoria's Secret, Marks & Spencer, and Adore Me all have slightly different fits even when labeled the same size. Additionally, different bra styles (balconette, plunge, sports) fit differently even within the same brand. Always check brand-specific sizing charts and read reviews about fit before purchasing.

Measure with either no bra or a non-padded, unlined bra for the most accurate results. Padded bras, push-ups, or heavily molded cups add extra bulk that will throw off your bust measurement. For underbust measurement, you can measure with or without a bra since it shouldn't affect this measurement. If you must wear a bra while measuring, choose the thinnest, most basic style you own without padding or extra features.

A riding-up band indicates your band size is too large. The band provides 80% of a bra's support and should sit level around your torso. When it rides up, it can't provide proper support, causing straps to dig in and breast tissue to sag. Try going down one or two band sizes while going up in cup size accordingly (sister sizing). The band should be snug on the loosest hook when new, allowing you to tighten it as the elastic stretches over time.

Cup too small: breast tissue spills over the top or sides (quad-boob effect), underwire sits on breast tissue instead of on your ribcage, center gore doesn't lay flat against your sternum, or cups gap when you lean forward. Cup too big: wrinkles or gaps in the cup fabric, breast tissue doesn't fill the entire cup, underwire extends past your breast tissue, or the cups slide around when you move. A properly fitted cup encases all breast tissue completely without gaps or spillage.

No, a regular ruler won't work because you need a flexible measuring tape that can wrap around your body's curves. Use a soft fabric measuring tape (tailor's tape) specifically designed for body measurements. These are inexpensive and available at craft stores, sewing shops, or online. In a pinch, you can use a non-stretchy string or ribbon to wrap around your body, then measure that length against a ruler, but a proper measuring tape is strongly recommended for accuracy.

Sports bras come in two sizing formats: traditional band/cup sizing (like 34C) and simplified sizing (like S, M, L, XL). For band/cup sized sports bras, use the same size as your regular bras, though some brands run tighter for compression. For letter-sized sports bras, you'll need to consult the brand's conversion chart, as these vary significantly. High-impact sports bras often require more precise sizing than low-impact styles. Many athletes prefer band/cup sizing for better support and fit accuracy.

Yes, it's completely normal for breast size to fluctuate during your menstrual cycle due to hormonal changes. Many people experience temporary breast swelling and tenderness in the days before their period, which can make bras feel tighter, especially in the cup. This is why having a few bras in sister sizes can be helpful. Measure and calculate your bra size mid-cycle for the most consistent baseline. Water retention, caffeine intake, and sodium consumption can also affect temporary breast size changes.