If you've ever looked at a bra size calculator and wondered what on earth "over-bust" and "under-bust" actually mean, you're not alone.

These two simple measurements are the foundation of finding your correct bra size. Get them right, and you're much more likely to find a bra that feels comfortable, supportive, and made for your body.

Let's break it down.

What Is an Over-Bust Measurement?

Your over-bust measurement is taken around the fullest part of your bust.

This measurement helps determine your cup size and gives an indication of how much breast volume your bra needs to accommodate.

How to Measure Your Over-Bust

1. Stand upright with your arms relaxed at your sides.
2. Wrap a soft measuring tape around the fullest part of your bust, usually across the nipples.
3. Make sure the tape is level all the way around and sits comfortably against your body.
4. Record the measurement in inches or centimetres.

Top tip: Avoid pulling the tape too tightly. You want an accurate measurement, not a squeezed one.

What Is an Under-Bust Measurement?

Your under-bust measurement is taken directly underneath your breasts, around your ribcage.

This measurement helps determine your band size, which is arguably the most important part of your bra fit.

In fact, around 80% of your bra's support should come from the band, not the straps.

How to Measure Your Under-Bust

1. Stand comfortably with your arms relaxed.
2. Place the measuring tape directly underneath your bust where your bra band naturally sits.
3. Keep the tape level and snug against your ribcage.
4. Record the measurement.

The tape should feel firm but comfortable, not restrictive.

Why Are These Measurements Important?

Your over-bust and under-bust measurements work together to create your bra size.

The under-bust measurement helps establish your band size.

The difference between your over-bust and under-bust measurements helps determine your cup size.

Simple, right?

How Bra Size Is Calculated

Let's look at an example.

Step 1: Measure Your Under-Bust

Let's say your under-bust measurement is 34 inches.

This would usually indicate a 34 band size.

Step 2: Measure Your Over-Bust

Now let's say your bust measurement is 37 inches.

Step 3: Calculate the Difference

37 inches minus 34 inches equals a 3-inch difference.

Step 4: Determine Your Cup Size

Generally:

• 1 inch difference = A cup
• 2 inches difference = B cup
• 3 inches difference = C cup
• 4 inches difference = D cup
• 5 inches difference = DD/E cup
• 6 inches difference = F cup

And so on.

In this example, a 3-inch difference would suggest a 34C bra size.

A Few Things to Remember

Bra sizing is a brilliant starting point, but it isn't an exact science.

Different brands can fit differently.

Breast shape affects fit.

Different bra styles can feel completely different, even in the same size.

That's why it's important to focus on how a bra feels rather than becoming attached to a particular number or letter.

Tips for Measuring Yourself at Home

For the most accurate results:

• Use a soft measuring tape
• Measure while braless or wearing a non-padded bra
• Take measurements more than once
• Stand naturally without holding your breath
• Double-check your results
• And remember, measurements are a guide, not a rulebook.

The Bottom Line

Understanding your over-bust and under-bust measurements is the first step towards finding a bra that truly fits.

Your under-bust measurement helps determine your band size.

Your over-bust measurement helps determine your cup size.

Together, they create the foundation for comfort, support, and confidence.

Because when your bra fits properly, everything feels better.