UK Bra Size Calculator
UK bra sizing has its own cup sequence, and it stops matching American sizing as soon as you go past a DD. This guide shows you how to measure properly in inches or centimetres, how the UK cup letters actually run, and how your size translates to US and EU labels. Enter your measurements in the calculator on the home page to get all three at once.
You can use it as a bra size calculator for UK inches or as a UK bra size calculator in cm. The calculator converts the units for you, then shows the UK size alongside US and EU equivalents.
How to Measure Your UK Bra Size
You only need a soft tape measure and two numbers. Measure in a non-padded bra, or without one, and keep the tape level all the way round.
- Underband: Measure firmly around your ribcage, directly beneath your bust. Pull it snug — this measurement should feel tight. Round to the nearest whole inch (or centimetre).
- Bust: Measure loosely around the fullest part of your bust, keeping the tape parallel to the floor. Don't compress the tissue.
- Cup: Subtract the underband number from the bust number. Each inch of difference is one cup size, following the UK sequence in the chart below.
Do not add 4 inches. Older UK size charts told you to add 4 or 5 inches to your underband measurement. That instruction dates from an era of rigid, non-stretch fabrics and it is no longer used by UK bra fitters. Modern bras contain a high proportion of elastane, so adding inches simply gives you a band that rides up and stops supporting you. Our calculator uses your raw underband measurement — sometimes called the ribcage method or "plus zero".
UK Cup Size Chart
The UK cup sequence alternates single and double letters after D. This is the part that catches people out, because a UK F is not the same cup as an American F.
| Difference (inches) | Difference (cm) | UK cup |
|---|---|---|
| 1" | 2.5 cm | A |
| 2" | 5 cm | B |
| 3" | 7.5 cm | C |
| 4" | 10 cm | D |
| 5" | 12.5 cm | DD |
| 6" | 15 cm | E |
| 7" | 18 cm | F |
| 8" | 20 cm | FF |
| 9" | 23 cm | G |
| 10" | 25 cm | GG |
| 11" | 28 cm | H |
| 12" | 30 cm | HH |
| 13" | 33 cm | J |
| 14" | 35 cm | JJ |
| 15" | 38 cm | K |
UK to US Bra Size Conversion
Band numbers are identical — a UK 34 band is a US 34 band. Cup letters are also identical up to and including DD. Above DD the two systems split: the UK carries on through the alphabet using double letters, while US brands stack extra Ds and then skip ahead.
| Difference | UK cup | US cup |
|---|---|---|
| 4" | D | D |
| 5" | DD | DD |
| 6" | E | DDD |
| 7" | F | G |
| 8" | FF | H |
| 9" | G | I |
| 10" | GG | J |
| 11" | H | K |
| 12" | HH | L |
So a UK 34E is a US 34DDD, and a UK 30FF is a US 30H. If you buy from an American brand and order your UK letter directly, you will almost always end up with a cup that is too small.
UK to EU Bra Size Conversion
European labels work differently again. The band number is your underband measurement in centimetres, rounded to the nearest 5, so the numbers look nothing like UK ones.
| UK / US band | Underband (approx.) | EU band |
|---|---|---|
| 28 | 71 cm | 70 |
| 30 | 76 cm | 75 |
| 32 | 81 cm | 80 |
| 34 | 86 cm | 85 |
| 36 | 91 cm | 90 |
| 38 | 97 cm | 95 |
| 40 | 102 cm | 100 |
EU cup letters run in a single unbroken sequence, so a UK DD becomes an EU E, a UK E becomes an EU F, and a UK FF becomes an EU H. Exact cup labelling varies a little between European brands, so treat the conversion as a starting point rather than a guarantee.
Why the "+4 Method" Disappeared
If you were measured in a UK shop years ago, you were probably told to add 4 inches to your underband. It is worth understanding why that changed, because it explains why so many people are wearing a band that is two sizes too big.
When the modern sizing system was introduced, bras were made from rigid, largely non-stretch fabric. The extra inches were a practical allowance so the band could be done up at all. Retailers also used the addition to keep new sizes roughly aligned with the older ones women were used to.
Neither reason survives today. Almost every bra now contains elastane, so the band stretches to fit. Adding four inches on top of that produces a band that slides up your back during the day, which in turn pushes the support onto your shoulders — the usual cause of straps digging in. A correctly fitted band should do most of the work, sitting level and firm all the way round.
Checking the Fit
The calculator gives you a starting size. These four checks tell you whether it is actually right:
- Band: Level around your back and firm on the loosest hook, so it has room to be tightened as it wears in. You should be able to slide two fingers underneath, no more.
- Cups: All the breast tissue contained, with no spillage at the top or under the arm, and no gaping or wrinkling of the fabric.
- Straps: Comfortable, adjustable, and carrying only a small share of the weight. If loosening them makes the bra fall down, your band is too big.
- Centre gore: On an underwired bra, the panel between the cups should sit flat against your breastbone.
Sizing at UK High Street Brands
UK retailers do not all cut to the same block. Marks & Spencer, Next, Boux Avenue and Bravissimo can each fit slightly differently at the same nominal size, and cup depth in particular varies. Bravissimo and other specialists carry a much wider range of cup sizes above a DD than most general retailers do.
If you are comparing this result with an M&S, Bravissimo, Asda, or Next size guide, treat the calculated size as the starting point and then check that retailer's own fit notes. This page is not an NHS bra size calculator and does not claim medical endorsement; it is a practical fitting guide for shopping and size conversion.
If your calculated size is unavailable, a sister size will give you the same cup volume on a different band: go down one band and up one cup, or up one band and down one cup. A UK 34F and a UK 32FF hold roughly the same amount.
Frequently Asked Questions
Should I measure in inches or centimetres?
Either. UK sizing is built on inches, but you can measure in centimetres and let the calculator convert. Just don't mix units between the two measurements.
Can I use this bra size calculator for UK inches?
Yes. UK sizing is based on inch differences between the underband and bust measurement, so inches are the clearest unit to use if you have a tape measure marked in inches.
Can I use this UK bra size calculator in cm?
Yes. Measure the underband and bust in centimetres and the calculator will convert them before giving a UK size. Keep both measurements in the same unit.
Is this the same as an M&S or NHS bra size calculator?
No. This is an independent calculator and does not claim to be an M&S or NHS tool. It uses a modern measurement method and explains why retailer size charts can still vary.
Is a UK F cup the same as a US F cup?
No. A UK F is a US G. The two systems match up to DD and then diverge, because the UK inserts double letters (DD, E, F, FF, G, GG) while US brands go DD, DDD, then G, H, I.
Why did my size change from what I was measured at before?
Most likely because the old measurement added 4 inches to your band. Dropping that addition typically moves you down one or two band sizes and up a corresponding number of cup sizes — a 38C measured the old way is often a 34E or 34F measured properly.
How often should I re-measure?
Roughly once a year, and after any noticeable change in weight, pregnancy, or breastfeeding. Bands also stretch with wear, which is why you should buy on the loosest hook.
My measurement falls between two cup sizes. Which do I choose?
Try the larger cup first, particularly in an underwired style — a cup that is slightly roomy is far more comfortable than one that cuts in. Then use sister sizing to fine-tune the band.