Bra Size Calculator

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bra size calculator
United States (US / UK)European (EU – cm)
Inches (in)Centimeters (cm)
Result:
Enter measurements above
function calculateBraSize(){var ub=parseFloat(document.getElementById('underbust').value);var b=parseFloat(document.getElementById('bust').value);var unit=document.getElementById('units').value;var method=document.getElementById('calc_method').value;var showSteps=document.getElementById('steps').checked;if(isNaN(ub)||isNaN(b)){alert('Please enter valid numerical measurements.');return;}if(unit==='cm'){ub=ub/2.54;b=b/2.54;}var band;if(Math.round(ub)%2===0){band=Math.round(ub)+4;}else{band=Math.round(ub)+5;}var diff=Math.round(b-band);var cupLabels=['AA','A','B','C','D','DD','DDD/E','F','G','H','I','J'];var cup=";if(diff=cupLabels.length){cup='K+';}else{cup=cupLabels[diff];}var finalSize=band+cup;document.getElementById('sizeValue').innerHTML="Your Estimated Bra Size: "+finalSize;if(showSteps){var stepsHtml="
Calculation Steps:
";stepsHtml+="1. Band Size: "+Math.round(ub)+"\" + "+(Math.round(ub)%2===0?4:5)+" = "+band+"
";stepsHtml+="2. Cup Difference: "+Math.round(b)+"\" (Bust) – "+band+" (Band) = "+diff+"\"
";stepsHtml+="3. Cup Letter: "+cup+"
";stepsHtml+="4. Sister Sizes: "+(band-2)+(cupLabels[diff+1]||'N/A')+" or "+(band+2)+(cupLabels[diff-1]||'N/A');document.getElementById('stepDetails').innerHTML=stepsHtml;document.getElementById('stepDetails').style.display='block';}else{document.getElementById('stepDetails').style.display='none';}}

How to Use the Bra Size Calculator

Finding the perfect fit doesn't have to be a guessing game. This bra size calculator helps you find your starting point by using the industry-standard "Step 1/Step 2" measurement method. Because different brands use slightly different scales, having your precise measurements in inches or centimeters is the most reliable way to shop.

To get the most accurate result from the bra size calculator, you will need a flexible measuring tape and should ideally measure while wearing a non-padded bra or no bra at all.

Underbust (Ribcage)
Measure directly under your breasts, around your ribcage. Keep the tape level and snug, but not so tight that it cuts into your skin. This measurement determines your band size.
Full Bust
Measure across the fullest part of your chest (usually across the nipples). Hold the tape somewhat loosely so you don't compress the breast tissue, ensuring the tape is level around your back.
Sizing System
Choose between US/UK sizing (common for brands like Victoria's Secret or Maidenform) or EU sizing (common in Europe, measured in cm).

How It Works: The Math of Bra Fitting

Most modern commercial bra sizing follows a specific mathematical relationship between your ribcage and your bust volume. The formula used by this bra size calculator is based on the "Plus Four" method, which remains the standard for most major retailers.

Cup Size Index = Full Bust Measurement – Calculated Band Size

  • Band Calculation: If your underbust is an even number, we add 4 inches. If it is an odd number, we add 5 inches. This creates the "Band Size" (32, 34, 36, etc.).
  • Cup Determination: We subtract the Band Size from the Full Bust measurement. Each inch of difference represents one cup letter.
  • The 1-Inch Rule: 1 inch = A, 2 inches = B, 3 inches = C, 4 inches = D, and so on.

Calculation Example

Example: Let's say a user measures their underbust at 30 inches and their full bust at 35 inches.

Step-by-step solution:

  1. Underbust: 30″ (Even number)
  2. Calculate Band: 30 + 4 = 34
  3. Full Bust: 35″
  4. Calculate Difference: 35 – 34 = 1″
  5. Result: 1 inch difference corresponds to an "A" cup. The final size is 34A.

Common Questions

What are "Sister Sizes"?

Sister sizes are groups of bra size equivalents that have the same cup volume. For example, if a 34C feels too tight in the band, you might try a 36B. The cup volume remains the same, but the band length increases. Conversely, if the band is too loose, you would try a 32D.

Why does the bra size calculator add 4 or 5 inches to the band?

This is a traditional manufacturing standard. Historically, bra fabrics weren't as stretchy as modern spandex/elastane blends. While some modern "fit experts" suggest using your raw underbust measurement as your band size, most major brands still manufacture their products to fit based on the +4 formula.

How should a bra fit correctly?

The band should be level all the way around your back and snug enough that only two fingers can fit under it. The cups should hold all breast tissue without "spilling over" the top or having gaps/wrinkles in the fabric. The center gore (the part between the cups) should sit flat against your breastbone.

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