Find your perfect fit using standard industry measurements
Inches (Standard)
Centimeters (Metric)
Understanding How to Measure Your Bust Size
Wearing the correct bra size is essential not just for comfort, but for posture and long-term breast health. Statistics suggest that nearly 80% of women are wearing the wrong bra size. Our calculator uses the standard difference-based method to help you find a starting point for your perfect fit.
Step 1: Measure Your Underbust (Band Size)
Wrap a measuring tape snugly around your ribcage, directly under your breasts. The tape should be level and tight but not digging in. If you are measuring in inches, this measurement is the foundation of your band size. Our calculator automatically adjusts this to the nearest even number to give you your band size.
Step 2: Measure Your Bust (Cup Size)
Wrap the tape around the fullest part of your bust (usually at the nipple level). Keep the tape parallel to the floor, but do not pull it tight—it should rest gently against your skin without compressing the breast tissue.
How the Math Works
The "Cup Size" is determined by the difference between your bust measurement and your band size:
1 inch difference: A Cup
2 inch difference: B Cup
3 inch difference: C Cup
4 inch difference: D Cup
Practical Fitting Example
Let's say your Underbust is 31.2 inches and your Overbust is 35.1 inches.
The calculator rounds 31.2 to the nearest even number, which is 32. This is your Band Size.
Subtract 32 from 35.1, resulting in 3.1.
A 3-inch difference corresponds to a C Cup.
Your estimated size would be 32C.
Expert Tip: Different brands use different sizing standards (UK vs. US vs. EU). This calculator uses standard US sizing. If you find the cup is too small but the band is perfect, try one cup size up. If the band rides up your back, it's too big—try a smaller band size and a larger cup size.
function updateLabels() {
var unit = document.getElementById("unitType").value;
var labelUnderbust = document.getElementById("labelUnderbust");
var labelOverbust = document.getElementById("labelOverbust");
if (unit === "cm") {
labelUnderbust.innerText = "Underbust (cm)";
labelOverbust.innerText = "Bust (cm)";
} else {
labelUnderbust.innerText = "Underbust (Inches)";
labelOverbust.innerText = "Bust (Inches)";
}
}
function calculateBraSize() {
var unit = document.getElementById("unitType").value;
var rawUnderbust = parseFloat(document.getElementById("underbust").value);
var rawOverbust = parseFloat(document.getElementById("overbust").value);
var resultDiv = document.getElementById("braResult");
var sizeOutput = document.getElementById("sizeOutput");
var detailsOutput = document.getElementById("detailsOutput");
if (isNaN(rawUnderbust) || isNaN(rawOverbust) || rawUnderbust <= 0 || rawOverbust <= 0) {
alert("Please enter valid positive measurements.");
return;
}
if (rawOverbust <= rawUnderbust) {
alert("Bust measurement must be larger than Underbust measurement.");
return;
}
var ubInches = rawUnderbust;
var obInches = rawOverbust;
// Convert to inches for calculation if unit is cm
if (unit === "cm") {
ubInches = rawUnderbust / 2.54;
obInches = rawOverbust / 2.54;
}
// Step 1: Calculate Band Size
// Industry standard: If even, use that. If odd, round up or add 1.
var bandSize = Math.round(ubInches);
if (bandSize % 2 !== 0) {
bandSize += 1;
}
// Step 2: Calculate Difference
var diff = Math.round(obInches – bandSize);
// Step 3: Map Difference to Cup
var cup = "";
if (diff 10) {
cup = "K+";
}
resultDiv.style.display = "block";
sizeOutput.innerText = bandSize + cup;
var unitText = (unit === "inches") ? "in" : "cm";
detailsOutput.innerHTML = "Estimated Band Size: " + bandSize + "Estimated Cup Size: " + cup + "Based on a difference of approx. " + diff + " inches between adjusted measurements.";
// Smooth scroll to result
resultDiv.scrollIntoView({ behavior: 'smooth', block: 'nearest' });
}