How to Measure Your Bra Size When You're Full Bust (and Why the Charts Keep Lying)

If you have measured yourself three times and got three different answers, you are not doing it wrong. The charts are.

Here is the thing nobody says out loud. Most bra size calculators were built around a narrow slice of bodies, then stretched to cover everyone else. If you are full bust, the maths starts drifting the moment your ribcage and your bust are far apart. That gap is exactly where the popular formulas fall over.

So let us do it properly. It takes two minutes and a soft tape measure.

Step one: your band

Wrap the tape around your ribcage, directly under your bust. Snug. Level all the way round, front and back. If it slopes up at the back, your number will be wrong before you start.

Breathe out. Read the number. That is your band. Round to the nearest whole number and move on.

Do not add four inches. Do not add five. That add four rule is a leftover from the 1930s, when band elastic barely stretched at all. Your bra stretches. Adding four inches to a modern band is how you end up hitching it down at eleven in the morning.

Step two: your bust

Measure loosely around the fullest part of your bust. Tape level, relaxed, nothing squashed. Wear a thin non padded bra or nothing at all, because a padded cup will hand you an inch you do not actually have.

Step three: the difference is your cup

Subtract your band from your bust. Every inch of difference is one cup size.

• 1 inch is an A
• 2 is a B
• 3 is a C
• 4 is a D
• 5 is a DD
• 6 is a DDD or F, depending on the brand
• 7 is a G, and it keeps going

That is the whole formula. There is nothing else to it.

Why your result might feel wrong

If you have worn a 40C for a decade and the tape says 34G, your first instinct is that the tape is broken. It is not.

Those two sizes hold a similar volume. The difference is where the support comes from. In the 40C the band is loose and your straps are doing the lifting. In the 34G the band does the work and your shoulders get the day off.

Big cup letters scare people. They should not. A G cup on a 34 band is nothing like a G cup on a 44 band. The letter only means something next to the number.

The bit the charts skip

Your size is a starting point, not a verdict. Two bras in the same size can fit completely differently depending on cup shape, how the wire is drawn, and whether the band has a firm or soft stretch.

So measure, get your number, then treat it as a first guess. Try the band on the loosest hook, never the tightest. New elastic should feel firm. It relaxes over the first few weeks, and those spare hooks are what you tighten into across the year.

If you land between sizes

Go down a band and up a cup. A 38D and a 36DD hold roughly the same volume, but the 36 gives you a firmer anchor. That trick is called sister sizing and it is worth knowing.

Still not sure

Send us your two numbers and tell us what is going wrong right now. Riding up, digging in, spilling over the top, gapping at the edge. Each of those points at something specific, and we can usually narrow it down in one reply.

No chatbot, no script. Just someone who knows the charts lie.