bra size calculator

How to measure your bra size at home

You need a soft measuring tape and a mirror. Wear no bra or a thin, unpadded one, and stand straight with your arms relaxed.

1. Underbust: wrap the tape around your ribcage directly under your bust. Keep it level all the way round and snug, but not digging in. Breathe out before you read the number.
2. Bust: wrap the tape around the fullest part of your bust and across your back. Keep it level and loose enough that it does not squash the breast tissue.
3. Enter both numbers above, pick inches or centimeters, and read your size.

How this calculator works

Centimeter measurements are converted to inches first (divide by 2.54). The cup letters then follow the chart below. Band numbers are converted to EU and AU using the commonly published size charts.

Cup size chart (bust minus band, in inches)

Band size chart

Solved examples

Example 1: underbust 30 in, bust 33 in

Band = 30. Difference = 33 − 30 = 3, which is a C cup. Your size is 30C in US and UK sizing, 65C in EU and 8C in AU. Sister sizes: 32B and 28D.

Example 2: underbust 76 cm, bust 92 cm

76 ÷ 2.54 = 29.9 in, so the band is 30. 92 ÷ 2.54 = 36.2 in, so the difference is about 6, which is DDD in the US and E in the UK. Your size is 30DDD (US), 30E (UK), 65F (EU) and 8E (AU).

Example 3: underbust 34 in, bust 38 in

Band = 34. Difference = 4, which is a D cup. Your size is 34D, 75D in EU and 12D in AU. Sister sizes: 36C and 32DD.

What are sister sizes?

Sister sizes hold roughly the same cup volume on a different band. Go up one band size and down one cup letter (34C becomes 36B), or go down one band size and up one cup letter (34C becomes 32D). They help when a bra fits in the cup but the band feels too loose or too tight, or when a style is out of stock in your usual size.

Why this calculator does not add 4 inches

Older guides told you to add 4 or 5 inches to your underbust to get the band size, then subtract that from your bust to get the cup. This often produced a band that is too loose and a cup that is too small, which is why many people feel their bras never fit. This calculator uses the snug underbust as the band size and measures the cup from that band. If you are used to your old size, compare the two: a 34B from the old method is often close to a 30D or 32C here.

How a well-fitting bra should feel

• Band: sits level around your back, snug enough to stay put but comfortable. It should do most of the support work, not the straps.
• Cups: your breast tissue fills the cup without spilling over the top or sides, and without gaps or wrinkles.
• Center panel: in an underwired bra it lies flat against your breastbone.
• Underwires: sit around the breast tissue, not on top of it.
• Straps: stay in place without digging in. If they slip or dig, check the band first.

Fit changes with weight, hormones, pregnancy, exercise and age, so it is worth re-measuring every six to twelve months.

Frequently asked questions

How do I calculate my bra size?

Measure your snug underbust and round it to the nearest even number in inches to get your band size. Then measure your bust at its fullest point and subtract the band size. Each inch of difference is one cup step, starting with A at 1 inch.

How accurate is a bra size calculator?

It gives a reliable starting point, but not a guaranteed final size. Brands cut bras differently, and breast shape, firmness and the style of bra all change how a size fits. Try the calculated size and its sister sizes, and use the fit checks above.

Should I measure with or without a bra?

Measure with no bra, or with a thin unpadded bra. A padded or lined bra adds volume and can push your bust measurement too high.

Are US, UK and EU cup sizes the same?

They match up to D. After that they differ. For example, 5 inches of difference is DD in the US and UK but E in the EU, and 6 inches is DDD in the US, E in the UK and F in the EU. The calculator shows all systems so you can shop in any of them.

My measurements fall between two sizes. What should I do?

If your underbust is between two even band sizes, try both and pick the one that feels snug but comfortable. If your cup difference is about halfway between two letters, try the smaller cup first and move up if there is spilling or gaping.

How often should I measure myself again?

Every six to twelve months, and any time your weight changes, you are pregnant or breastfeeding, or your usual bras stop fitting well.

What if my size is not on the chart?

This calculator covers band sizes 24 to 60 and cup differences up to 12 inches. If your measurements fall outside that range, a professional fitter or a specialist brand can help you find the right size.

Disclaimer: this calculator provides estimates for general guidance only. Bra sizing varies between brands and countries. If a bra causes pain, or you have a medical or surgical reason for needing a specific type of bra, speak to a qualified fitter or healthcare professional.