Bra sizing is a topic that sparks confusion, frustration, and even disbelief among many women. For decades, the "+4 method" has been a standard approach to bra fitting in many mainstream retail settings, yet it’s widely criticized for leading to ill-fitting bras.
The History of +4 Bra Sizing
The +4 method, which involves adding four inches to a woman’s underbust measurement to determine her band size, has roots in the evolution of bra sizing systems. Before the 1970s, bra sizing was less standardized. Back then, the number was your bust measurement, and the cup size was an approximation of how busty you were. That system relied on bust circumference, with cup sizes (A, B, C) loosely indicating breast size relative to the torso. Very subjective, clearly.
The modern bra sizing system, which uses underbust measurement for the band and the difference between underbust and bust for the cup, emerged in the mid-20th century. In 1975, European regulators mandated that bra sizes should be based on underbust measurements, a shift that aimed for greater accuracy. However, this change caused a backlash. Women accustomed to a 36 bust size, for example, were suddenly told their band size was closer to 30, which felt jarring. To ease this transition, manufacturers and retailers introduced the +4 method, adding four (or sometimes five) inches to the underbust measurement to align new sizes more closely with older ones. This was meant as a temporary solution, but it became entrenched, largely due to what some speculate is “profit and convenience” for manufacturers.
Some attribute the +4 method to the era when bras were made of non-stretchy materials, requiring looser bands to accommodate rib expansion during breathing. However, others debunk this, noting no historical data to actually back that up, and instead suggest that the method stemmed from vanity sizing—making women feel they fit into more familiar sizes.
In either case, this historical artifact of measuring has persisted, shaping how bras are sold today.
Current Use of +4 Bra Sizing
Despite advancements in bra design and fitting knowledge, the +4 method remains prevalent in mainstream retail, particularly in the U.S. and even in the UK. Major brands and stores (looking at you, Victoria’s Secret) often use this method or variations (e.g., +5 or diagonal measurements) to size customers. There are theories that retailers tell people to do this so they can justify fitting more people into fewer sizes. This approach allows companies to stock a narrower range of sizes—typically 32–38 bands with A–DD cups—while claiming to fit a broader population.
The +4 method is embedded in many bra size calculators on retail websites, perpetuating its use. This persistence is partly because it’s profitable: producing fewer sizes reduces manufacturing costs, and ill-fitting bras lead to frequent replacements. While this does definitely allow for a narrower range of inventory that "fits" a wider size range, it's more likely rooted in matching societal expectations (i.e. most think that a D cup is for "big boobs," which harkens back to the pre-70's sizing scale) than a nefarious money-grab.
However, the +4 method is less common in regions with more robust sizing standards, like the UK, where brands often carry wider size ranges (e.g., 28–44 bands, A–K+ cups). Even so, global retailers and fast-fashion brands continue to rely on outdated sizing practices, exacerbating fit issues.
Problems Associated with +4 Bra Sizing
The +4 method is notorious for causing a cascade of fit problems. Here are the key issues:
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Too-Loose Bands and Too-Small Cups: By adding four inches to the underbust, the +4 method results in a band that’s often too loose, reducing support. Simultaneously, it narrows the difference between underbust and bust measurements, leading to smaller cup sizes than needed. For example, someone with a 32-inch underbust and 38-inch bust might be fitted as a 36B using +4, when their true size is closer to 32DD. This mismatch causes discomfort, spillage, and lack of support.
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Physical Discomfort and Health Issues: Ill-fitting bras from +4 sizing can lead to pain and health problems. Issues like “quad boob,” where breast tissue spills over too-small cups, and bands riding up. Poorly fitting bras can exacerbate back pain, shoulder strain, and even heartburn from tight bands squishing the chest.
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Limited Size Availability: The +4 method funnels women into a narrow size matrix, making it hard to find true sizes, especially for smaller bands (e.g., 26–30) or larger cups (F+).
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Psychological Impact and Misconceptions: The +4 method reinforces outdated notions about bra sizes, like “D cups are huge” or “A cups are small.” Finding that you're a DD instead of a B can create disbelief. This sticker shock stems from cultural misconceptions perpetuated by +4 sizing, making women feel their bodies are abnormal when they don’t fit standard sizes.
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Economic and Accessibility Barriers: The +4 method’s reliance on mainstream sizes limits options for those outside the 32–38 A–DD range, historically requiring expensive boutique or online purchases. (We are changing that though!)
Moving Beyond +4: Solutions and Awareness
Many in the industry, including us, advocate for a more accurate sizing method using the A Bra That Fits calculator, which takes six measurements (three underbust, three bust) to account for shape and fit preferences. While it's far from perfect, it is amazingly helpful in getting on the right path to a well-fitted bra.
In the end, measurements are not everything. Fit is. Support is. Comfort is. There are myriads of brands, systems, opinions and measurement guides all trying to control how your bra fits. The key is to remain in control of your own fit and focus on how the cups fits your breasts, how the gore sits on your sternum, how the wire follows your breast outline, and how the band hugs your body. You can read more about how a bra should fit HERE, HERE and HERE.
Conclusion
The +4 bra sizing method, a relic of a transitional sizing shift, continues to dominate mainstream retail due to cost-saving and convenience for manufacturers. However, it leads to ill-fitting bras, physical discomfort, and psychological barriers for countless women. By understanding its history and flaws, and embracing accurate measurement guidelines and focusing on fit, bra wearers can find sizes that truly fit, proving that everyone deserves a bra that supports their body and confidence.
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