Bra Size Calculator

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bra size calculator
Inches (US/UK Standard)Centimeters (Metric)
Recommended Size:
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function calculateBraSize(){var ub=parseFloat(document.getElementById('input1').value);var b=parseFloat(document.getElementById('input2').value);var unit=document.getElementById('given_data').value;var showSteps=document.getElementById('steps').checked;if(isNaN(ub)||isNaN(b)){alert('Please enter valid measurements for Underbust and Bust');return;}if(b<=ub){alert('Bust measurement must be larger than Underbust measurement');return;}var workingUB=ub;var workingB=b;if(unit==='cm'){workingUB=ub/2.54;workingB=b/2.54;}var band=Math.round(workingUB);if(band%2!==0){band+=1;}var diff=Math.round(workingB-band);var cups=["AA","A","B","C","D","DD/E","DDD/F","G","H","I","J","K"];var cupStr="";if(diff=cups.length){cupStr=cups[cups.length-1];}else{cupStr=cups[diff];}document.getElementById('resultValue').innerHTML=band+cupStr;var sisterHtml="";if(showSteps){var upBand=band+2;var upCup=cups[Math.max(0,diff-1)]||"AA";var downBand=band-2;var downCup=cups[Math.min(cups.length-1,diff+1)];sisterHtml="Sister Sizes: "+downBand+downCup+" (tighter band) or "+upBand+upCup+" (looser band)";}document.getElementById('sisterSizes').innerHTML=sisterHtml;document.getElementById('answer').style.display='block';}

How to Use the Bra Size Calculator

Finding the perfect fit is essential for comfort, posture, and confidence. This bra size calculator helps you transition from confusing manual measurements to an accurate size estimate in seconds. By using your underbust and bust measurements, we apply the standard industry formula to determine your band and cup size.

To get the most accurate results, follow these steps with a flexible measuring tape:

Underbust Measurement
Measure directly under your breasts, where the bra band usually sits. Keep the tape snug and parallel to the floor. Exhale to get your smallest natural ribcage measurement.
Bust Measurement
Measure around the fullest part of your chest. Do not pull the tape tight; it should rest lightly against your skin without indenting the breast tissue.
Measurement System
Choose between Inches (standard for US/UK) or Centimeters (Metric) to ensure the math aligns with your preferred shopping region.

How the Calculation Works

The bra size calculator uses a two-step mathematical process based on the modern professional fitting method. Unlike older "add 4 inches" methods, this calculation prioritizes the actual ribcage size for better support.

Band Size = Underbust (rounded to nearest even number)
Cup Size = Bust Measurement – Band Size

  • Band Calculation: If your underbust is an even number, that is usually your band size. If it is odd, we round up to the next even number to ensure the band isn't restrictively tight.
  • Difference Index: Each inch of difference between the bust and the band corresponds to a cup letter.
  • Cup Mapping: 1 inch = A, 2 inches = B, 3 inches = C, 4 inches = D, 5 inches = DD, and so on.

Calculation Example

Example Scenario: Sarah wants to find her new size after noticing her current bras are uncomfortable. She takes her measurements in inches.

Step-by-step solution:

  1. Underbust Measurement: 31 inches.
  2. Bust Measurement: 35 inches.
  3. Band Logic: Since 31 is odd, we round up to 32. Band = 32.
  4. Cup Difference: 35 (Bust) – 32 (Band) = 3 inches.
  5. Result: A 3-inch difference equals a "C" cup. Final Size = 32C.

Common Questions

Why does the calculator give me a different size than I currently wear?

Many people wear a band that is too large and a cup that is too small. The bra size calculator focuses on the ribcage measurement to provide the necessary 80% of support that should come from the band, rather than the shoulder straps.

What are "Sister Sizes"?

Sister sizes are bra sizes where the cup volume remains the same even though the band size and cup letter change. For example, if a 34C feels too tight in the band, a 36B will have the same cup volume but a looser fit around the ribs.

How often should I recalculate my size?

It is recommended to use a bra size calculator every 6 to 12 months. Weight fluctuations, hormonal changes, and exercise can all alter your breast tissue and ribcage measurements significantly over a short period.

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