Find your perfect fit using standard US measurements
Measure snugly around your ribcage, directly under your bust.
Measure around the fullest part of your chest while wearing a non-padded bra.
Your Estimated US Bra Size is:
Please enter valid measurements for both fields.
How to Measure for Your US Bra Size
Finding the right bra size is essential for comfort, posture, and support. In the United States, bra sizes consist of a number (the band size) and a letter (the cup size). Follow these steps to get the most accurate results from our Bra Size Calculator USA.
1. Find Your Band Size
Wrap a soft measuring tape around your ribcage, directly under your breasts. The tape should be level and snug. If the number is even, add 4 inches. If it is odd, add 5 inches. For example, if you measure 30 inches, your band size is 34. If you measure 31 inches, your band size is 36.
2. Find Your Bust Measurement
Measure around the fullest part of your bust (usually at the nipple line). Hold the tape somewhat loosely so you don't compress the tissue, but ensure it is level across your back.
3. Calculate the Cup Size
Subtract your calculated band size from your bust measurement. Each inch of difference corresponds to a cup letter.
Difference (Inches)
US Cup Size
Less than 1″
AA
1″
A
2″
B
3″
C
4″
D
5″
DD (E)
6″
DDD (F)
7″
G
8″
H
Common Signs of a Poorly Fitting Bra
Band riding up: Your band is likely too large. The band should sit level around your body.
Spilling over: If you are "double-boobing" over the top or sides, the cup size is too small.
Straps digging in: This usually means the band is too loose and isn't providing the 80% support it should.
Gaping cups: If there is space between you and the bra, the cup size may be too large or the style is wrong for your shape.
function calculateBraSize() {
var underbust = parseFloat(document.getElementById('underbust').value);
var bust = parseFloat(document.getElementById('bust').value);
var resultArea = document.getElementById('result-area');
var finalSize = document.getElementById('final-size');
var sizeDetails = document.getElementById('size-details');
var errorMsg = document.getElementById('error-message');
// Reset visibility
resultArea.style.display = 'none';
errorMsg.style.display = 'none';
if (isNaN(underbust) || isNaN(bust) || underbust <= 0 || bust <= 0) {
errorMsg.style.display = 'block';
return;
}
if (bust <= underbust) {
errorMsg.innerText = "Bust measurement must be larger than underbust measurement.";
errorMsg.style.display = 'block';
return;
}
// Standard US Band Calculation (The +4/+5 Rule)
var bandSize;
var roundedUnderbust = Math.round(underbust);
if (roundedUnderbust % 2 === 0) {
bandSize = roundedUnderbust + 4;
} else {
bandSize = roundedUnderbust + 5;
}
// Calculate Cup
var difference = Math.round(bust – bandSize);
var cupLetters = ["AA", "A", "B", "C", "D", "DD", "DDD", "G", "H", "I", "J", "K", "L", "M"];
var cupIndex = difference;
// Adjust index if negative or zero
var cupResult = "";
if (difference = cupLetters.length) {
cupResult = "Specialist Size";
} else {
cupResult = cupLetters[cupIndex];
}
// Display Result
finalSize.innerText = bandSize + cupResult;
sizeDetails.innerText = "Calculated using a " + bandSize + "-inch band and a " + difference + "-inch cup difference.";
resultArea.style.display = 'block';
}