Formula
Cup Size = Bust Measurement - Band Measurement
Measure band snugly under bust, measure bust at fullest point. The difference in inches determines cup size (1 inch=A, 2 inches=B, etc.).
Worked Examples
Example 1: Standard Calculation
Problem: Band measure: 30 inches, Bust: 34 inches.
Solution: Band size = 30 (round to even)\n\nDifference = 34 - 30 = 4 inches\n\n4 inches = D cup\n\nSize: 30D
Result: 30D
Example 2: Sister Size Example
Problem: Wearing 34B but band feels loose.
Solution: Current: 34B\nBand loose โ go down in band\n\nSister size down: 32C\n(Same cup volume, tighter band)\n\nTry 32C for better support.
Result: Try 32C
Example 3: Metric Conversion
Problem: Band: 75 cm, Bust: 90 cm.
Solution: Convert to inches:\nBand: 75 รท 2.54 โ 29.5 โ 30\nBust: 90 รท 2.54 โ 35.4\n\nDiff = 35 - 30 = 5 inches = DD\n\nSize: 30DD (US) or 65E (EU)
Result: 30DD / 65E
Frequently Asked Questions
How do I measure my bra size?
Measure band: around ribcage, directly under bust, snugly. Measure bust: around fullest part, loosely. The difference determines cup size. Wear an unpadded bra or no bra.
Why doesn't my calculated size feel right?
Sizing varies by brand. Breast shape, spacing, and fullness affect fit beyond size. Try your calculated size plus sister sizes. Consider professional fitting for best results.
How should a properly fitting bra feel?
Band: snug, parallel to floor, 2 fingers fit underneath. Cups: no spillage or gaping. Straps: supportive but not digging. Center: sits flat against sternum.
What is band size?
Band size is the circumference of your ribcage just below the bust, measured in inches (US/UK) or centimeters (EU). It should be snug for support.
How is cup size determined?
Cup size = bust measurement - band measurement. Each inch of difference is roughly one cup size: 1\"=A, 2\"=B, 3\"=C, 4\"=D, 5\"=DD, etc.
Can I use Bra Size Calculator on a mobile device?
Yes. All calculators on NovaCalculator are fully responsive and work on smartphones, tablets, and desktops. The layout adapts automatically to your screen size.
Background & Theory
The Bra Size Calculator applies the following established principles and formulas.
Fitness and nutrition science rests on well-characterized biochemistry and exercise physiology. Macronutrients provide the caloric substrate for all biological activity: protein yields 4 kilocalories per gram, carbohydrates yield 4 kilocalories per gram, and dietary fat yields 9 kilocalories per gram. These values, established by Wilbur Atwater in the early 1900s through bomb calorimetry, underpin all dietary energy calculations and macro-ratio planning for performance and body composition goals.
One-repetition maximum, or 1RM, represents the highest load an individual can lift for a single complete repetition. The Epley formula estimates it as weight lifted multiplied by (1 + reps/30), while the Brzycki formula uses weight divided by (1.0278 โ 0.0278 ร reps). These formulas, validated across compound movements, allow athletes to program training intensity as a percentage of 1RM without maximal testing on every exercise.
VO2 max, the maximum volume of oxygen consumed per kilogram of body weight per minute, is the gold standard measure of aerobic capacity and cardiovascular fitness. Field estimates use submaximal tests such as the Cooper 12-minute run, step tests, or resting heart rate-based equations. Higher VO2 max correlates strongly with reduced all-cause and cardiovascular mortality in population studies.
Delayed onset muscle soreness is a normal inflammatory response to unaccustomed eccentric loading, peaking 24 to 72 hours after exercise. The physiological basis involves micro-trauma to myofibrils and subsequent prostaglandin-mediated inflammation. Progressive overload, the systematic increase of training volume or intensity over time, is the primary driver of skeletal muscle hypertrophy and strength adaptation, working through mechanotransduction pathways that upregulate mTOR signaling and protein synthesis.
Protein synthesis requirements for muscle retention and growth, supported by research from the International Society of Sports Nutrition, typically range from 1.6 to 2.2 grams per kilogram of body weight per day for active individuals, with intake distributed across meals to optimize leucine-driven anabolic signaling.
History
The history behind the Bra Size Calculator traces back through the following developments.
The formal pursuit of physical culture as a discipline dates to the late 19th century. Eugen Sandow, the German-born showman often called the father of modern bodybuilding, popularized structured resistance training and physique development in the 1890s, touring with live exhibitions and publishing training guides that influenced a generation of physical educators. His emphasis on measurement, proportionality, and exercise prescription introduced an empirical framework to strength training.
The revival of the Olympic Games in Athens in 1896 by Pierre de Coubertin institutionalized competitive athletics globally and accelerated interest in sports science. Physical education programs expanded through the early 20th century in Europe and North America, and military fitness standards during both World Wars generated large datasets on human physical capacity.
The American College of Sports Medicine, founded in 1954, was the first major scientific organization dedicated to exercise science, producing research guidelines on training prescription, physical fitness testing, and health-related fitness standards. ACSM's fitness testing protocols and exercise intensity guidelines remain foundational references today.
Kenneth Cooper's 1968 book Aerobics introduced the concept of quantified aerobic fitness to popular audiences, coining the term and providing a points-based system for measuring and accumulating aerobic exercise. His 12-minute run test for VO2 max estimation became standard in fitness assessments worldwide and inspired the global aerobics fitness movement of the 1970s and 1980s.
Sports nutrition as a formalized science emerged through the 1980s and 1990s, with the isolation of creatine's performance effects, the characterization of glycogen depletion and carbohydrate loading, and the first controlled trials on protein supplementation for strength athletes. The International Society of Sports Nutrition, founded in 2003, subsequently produced consensus position statements on protein, creatine, and other ergogenic aids grounded in systematic evidence reviews. The CrossFit movement, growing from the early 2000s, popularized functional fitness benchmarks and introduced structured intensity metrics to everyday gym culture.