Find your perfect fit using standard US/UK sizing logic.
Measure snugly around your ribcage, just under your breasts.
Measure around the fullest part of your chest while wearing a non-padded bra.
Your Estimated Bra Size:
How to Use This Bra Cup Calculator
Wearing the wrong bra size isn't just uncomfortable; it can lead to back pain, poor posture, and skin irritation. This calculator uses the traditional "Step 2" method used by most major retailers to determine your band and cup size.
Step 1: Measure Your Underbust
Exhale to get your smallest measurement. Wrap a soft measuring tape snugly around your ribcage directly under your bust. If your measurement is an even number, add 4 inches. If it is an odd number, add 5 inches. This calculation gives you your Band Size.
Step 2: Measure Your Bust
Wrap the tape measure around the fullest part of your chest. Ensure the tape is level across your back. Do not pull it too tight; it should just rest on the surface.
Step 3: Calculate the Difference
Subtract your calculated Band Size from your Bust Measurement. Each inch of difference represents one cup size:
0 inches: AA
1 inch: A
2 inches: B
3 inches: C
4 inches: D
5 inches: DD (E)
6 inches: DDD (F)
7 inches: G
Real-World Example
Let's look at a realistic scenario for a proper fitting:
Why do I add 4 or 5 inches to the underbust? This is a standard industry practice for US and UK sizing to account for the elasticity of the bra band and to ensure the wires do not dig into the ribcage.
What if I am between sizes? If your calculation falls between cups (e.g., a 2.5-inch difference), we recommend trying both the smaller and larger cup size. Bra fit can vary significantly between different brands and styles.
function calculateBraSize() {
var underbustInput = document.getElementById('underbust').value;
var bustInput = document.getElementById('bust').value;
var resultArea = document.getElementById('bra-result-area');
var errorDiv = document.getElementById('bra-error');
var successDiv = document.getElementById('bra-success');
var finalSizeDiv = document.getElementById('final-size');
var sizeNote = document.getElementById('size-note');
// Reset display
resultArea.style.display = 'block';
errorDiv.style.display = 'none';
successDiv.style.display = 'none';
var underbust = parseFloat(underbustInput);
var bust = parseFloat(bustInput);
if (isNaN(underbust) || isNaN(bust) || underbust <= 0 || bust <= 0) {
errorDiv.innerHTML = "Please enter valid measurements for both fields.";
errorDiv.style.display = 'block';
return;
}
if (bust < underbust) {
errorDiv.innerHTML = "Bust measurement should be larger than underbust measurement.";
errorDiv.style.display = 'block';
return;
}
// Step 1: Calculate Band Size (The +4/+5 rule)
var bandSize;
var roundedUnderbust = Math.round(underbust);
if (roundedUnderbust % 2 === 0) {
bandSize = roundedUnderbust + 4;
} else {
bandSize = roundedUnderbust + 5;
}
// Step 2: Calculate Cup
// Note: Cup is based on Bust – Band Size
var difference = Math.round(bust – bandSize);
var cupMap = [
"AA", // 0
"A", // 1
"B", // 2
"C", // 3
"D", // 4
"DD (E)", // 5
"DDD (F)", // 6
"G", // 7
"H", // 8
"I", // 9
"J", // 10
"K" // 11
];
var cupSize = "";
if (difference = cupMap.length) {
cupSize = "L+";
} else {
cupSize = cupMap[difference];
}
// Output
successDiv.style.display = 'block';
finalSizeDiv.innerHTML = bandSize + cupSize;
sizeNote.innerHTML = "Based on an underbust of " + underbust + "\" and a bust of " + bust + "\".";
}