Accurately determine your bra cup size using your band size and bust measurement.
Loose Underbust
Snug Underbust
Tight Underbust
Understanding Bra Sizing: The Key Metrics
Finding the right bra size is crucial for comfort, support, and confidence. While many factors contribute to a perfect fit, the primary measurements are your band size and your cup size. This calculator helps you determine your cup size based on standard industry practices.
Band Size: The Foundation
Your band size is the measurement around your rib cage, directly under your bust. It provides the primary support for the bra. This calculator accommodates three common underbust measurement types:
Loose Underbust: Measured loosely around the chest, similar to how you'd wear a bra but without any tension.
Snug Underbust: Measured with the tape measure snug against the body, providing a more accurate representation of the band size you'd typically wear. This is the most commonly used measurement for band size.
Tight Underbust: Measured with significant pressure, pulling the tape measure as tight as comfortably possible. This is often used to determine smaller band sizes or for specific fitting needs.
The calculator uses your chosen band size measurement to determine the base band number (e.g., 34, 36 inches). If your measurement doesn't directly match a standard band size, bra fitters often round to the nearest even number. For instance, a snug measurement of 33 inches would typically correspond to a 34 band size.
Bust Measurement: Determining the Cup
Your full bust measurement is taken around the fullest part of your bust, usually across the nipples. This measurement, when compared to your band size, determines the volume of your breasts and thus, your cup size.
The Calculation: Band vs. Bust
The core of bra sizing involves comparing your full bust measurement to your band size measurement. The difference between these two numbers dictates the cup size.
Here's the general principle:
Difference of 1 inch: AA Cup
Difference of 2 inches: A Cup
Difference of 3 inches: B Cup
Difference of 4 inches: C Cup
Difference of 5 inches: D Cup
Difference of 6 inches: DD/E Cup
Difference of 7 inches: DDD/F Cup
Difference of 8 inches: G Cup
…and so on, typically adding an inch for each subsequent cup size increase.
For example, if your band size is 34 inches and your full bust measurement is 37 inches, the difference is 3 inches (37 – 34 = 3). This difference typically corresponds to a B cup. Therefore, your calculated size would be 34B.
Important Considerations:
This is a guide, not a definitive rule. Bra fit can vary significantly between brands and styles.
The type of underbust measurement matters. Using the 'snug' measurement is generally recommended for accurate band sizing.
Body shape and breast tissue density also play a role in how a bra fits.
Always try bras on whenever possible. If you're ordering online, check the brand's specific size charts and return policies.
A perfectly fitting bra should have the band sitting parallel to the floor, the cups fully encasing the breast without gaping or spilling, and the straps staying comfortably in place without digging in.
Use this calculator as a starting point for finding a bra size that offers optimal comfort and support.
function calculateCupSize() {
varbandSizeInput = document.getElementById("bandSize");
var bustMeasurementInput = document.getElementById("bustMeasurement");
var measurementTypeSelect = document.getElementById("measurementType");
var resultDiv = document.getElementById("result");
varbandSize = parseFloat(bandSizeInput.value);
var bustMeasurement = parseFloat(bustMeasurementInput.value);
var measurementType = measurementTypeSelect.value;
// Clear previous result
resultDiv.innerHTML = "";
// Basic validation
if (isNaN(bandSize) || bandSize <= 0) {
resultDiv.innerHTML = "Please enter a valid Band Size.";
return;
}
if (isNaN(bustMeasurement) || bustMeasurement <= 0) {
resultDiv.innerHTML = "Please enter a valid Full Bust Measurement.";
return;
}
if (bustMeasurement <= bandSize) {
resultDiv.innerHTML = "Full Bust Measurement must be greater than Band Size.";
return;
}
// Determine the effective band size based on measurement type
var effectiveBandSize;
if (measurementType === "loose") {
// For loose, often add a bit to find the corresponding standard band
effectiveBandSize = Math.round(bandSize + 4) / 2 * 2;
} else if (measurementType === "snug") {
// Snug is usually the direct band size, rounded to nearest even
effectiveBandSize = Math.round(bandSize) / 2 * 2;
} else { // tight
// For tight, often subtract a bit to find the corresponding standard band
effectiveBandSize = Math.round(bandSize – 2) / 2 * 2;
}
// Ensure effectiveBandSize is at least 28 (a common minimum)
if (effectiveBandSize = 1.0 && difference = 1.5 && difference = 2.5 && difference = 3.5 && difference = 4.5 && difference = 5.5 && difference = 6.5 && difference = 7.5 && difference = 8.5 && difference = 9.5 && difference = 10.5 && difference = 11.5 && difference = 12.5) {
// For very large differences, continue the pattern or indicate beyond standard sizing
// This is a simplified progression. Real sizing is more complex.
// For simplicity, we'll cap at K or provide a general indication for larger values.
cupSize = "Larger than K";
} else {
cupSize = "Could not determine";
}
resultDiv.innerHTML = "Your estimated Bra Size is: " + effectiveBandSize + cupSize +
"(Based on measurements, fit may vary by brand)";
}