How to Measure Bra Size UK: Step-by-Step Fit Guide

Band size rule: Round underbust to nearest even inch ·
Cup size formula: Bust minus band in inches ·
Measurement posture: Tape level and parallel ·
Remeasure: Every 6–12 months

Below are the key bra sizing facts based on official sources.

How do I measure my bra size at home in the UK?

Two measurements give you the full picture: band size and bust size. Follow these steps from Triumph UK (lingerie brand) and National Breast Cancer Foundation (health charity) for consistent results.

1. Step 1 – Measure your band size
   • Place a soft tape measure directly under your bust, keeping it level and snug.
   • Breathe normally and take the measurement in inches. Triumph advises rounding to the nearest even inch for UK sizing.
   • If your underbust is 31 inches, your band size becomes 32. If it’s 32 inches, stay at 32.
2. Step 2 – Measure your bust size
   • Measure around the fullest part of your chest (nipple level), with the tape straight and parallel to the floor.
   • Keep the tape loose – don’t pull tight.
3. Step 3 – Calculate your cup size
   • Subtract your band measurement from your bust measurement. Each inch of difference equals one cup size: 1″ = A, 2″ = B, 3″ = C, and so on.
   • For example, if your bust is 36″ and band is 34″, the 2″ difference gives you a B cup.

How do I use the M&S bra size calculator?

Savers like M&S and Primark offer free online calculators that follow the same steps above. They ask for your underbust and bust in inches, then return a UK size. No brand’s calculator is perfect, though – always try the size on and adjust.

How can I measure my bra size online in the UK?

Online calculators are available from most UK lingerie retailers, including M&S, Primark, Bravissimo, and Triumph. They follow the same two‑measurement method. Enter your underbust and bust in inches, and the tool outputs a UK size. Remember that calculator results are a starting point — trust the real‑life fit.

How do I measure my bra size in inches?

Use a flexible tape measure marked in inches. UK sizing is based on inches, so stick to inches throughout. The Cosmic guide from Cosmopolitan UK (fashion magazine) also recommends the classic formula: add 4 inches to an even underbust (or 5 to an odd underbust) to get the band size, then calculate cup from the bust measurement. Note that many modern guides skip the +4 step and use the raw underbust number rounded even – both methods exist, so check the specific fit guide of the bra brand you’re buying.

How do I measure my bra size using UK NHS guidelines?

The NHS does not publish its own bra‑sizing guide, but its healthcare advice aligns with professional fitting standards – measure under the bust, keep tape level, and use the difference for cup size. For official health information, consult the NHS breast awareness page.

How do you calculate your cup size?

Cup size is simply the number of inches your bust is larger than your band. The math is straightforward – once you have both numbers, subtract them.

• 1 inch difference = A cup
• 2 inches = B cup
• 3 inches = C cup
• 4 inches = D cup (Boobydoo)
• 5 inches = DD cup, and so on, following UK cup progressions.

Posture matters: stand straight with arms relaxed and the tape parallel to the floor. Do not wear a padded bra while measuring – a non‑padded or no bra gives the most accurate result.

The implication: cup letters are meaningless without the band size. A 34C and a 38C hold very different volumes (see sister sizes below).

What is the 3 bra rule?

The 3 bra rule is a simple rotation system: one bra worn, one in the wash, and one ready. It extends the life of each bra by preventing daily wear and tear. Many lingerie experts, including Miss Mary, recommend it to maintain elasticity and shape.

What is the 2 finger rule for bras?

The 2 finger rule helps you check band tightness. After fastening your bra, try sliding two fingers under the band. If it’s too tight to fit, the band may be too small; if more than two fingers slide easily, the band is likely too large. The band should stay level across your back, not ride up. Straps should not dig in or fall off – that’s a sign the band may be doing too much work.

The implication: use these rules as starting points, not absolutes.

Is a 32C the same as a 34B?

Yes – 32C, 34B, and 36A are called “sister sizes”. They have the same cup volume, just on different band lengths. If your calculated size feels off in the band, moving to a sister size can fix the fit without changing the cup volume. Sister sizing works both ways: if a 34C band feels too tight, try a 36B (wider band, smaller cup, same volume).

Which is bigger, 36C or 38C?

A 38C is larger than a 36C in both band length and overall cup volume because the cup is wider and deeper to match the larger band. Cup letters alone don’t tell the full story – the band size determines the actual volume of the cup.

Is 34C small for a woman?

No, 34C is an average band/cup combo in the UK. Several retailers report 36C as the most common size, so 34C is close to the middle of the distribution. Bra size is highly individual – “small” is a subjective label, not a fit metric.

Below are sister size examples that illustrate the relationship.

The takeaway: if a 34B feels tight in the band, try a 36A. If the band is loose, try a 32C. Always adjust by one sister size at a time.

How do I convert international bra sizes?

UK and US sizes match up to DD cup, then diverge. A UK E cup is a US DDD/F, and UK F is US G. European band sizes are in centimetres – a 34 band roughly equals a 75 band. Conversion charts vary by brand, so always check the specific guide provided by the retailer.

How do I convert UK to US bra sizes?

• UK DD = US DD/E
• UK E = US DDD/F
• UK F = US G
• UK FF = US H

Wikipedia’s bra size article (reference source) provides a full cross‑referencing table. Online converters like the one from Cosmopolitan UK also help.

What is the EU sizing system?

EU band sizes are the underbust measurement in centimetres, rounded to the nearest 5. A 34‑inch underbust (about 86 cm) converts to an EU 85 band. Cup progressions are the same as UK – the difference in cm between bust and band determines the cup letter.

Measurement method comparison

Three popular guides, one core difference: the +4/+5 rule vs raw underbust. Here’s how they stack up:

Why this matters: if you follow a +4 guide, you may end up with a smaller band size than a direct measurement guide. Always try both methods if you’re between sizes, and trust the fit over the number.

“Measure around the fullest part of your chest and keep the tape straight across and around the back – not too tight, not too loose.”

– National Breast Cancer Foundation bra fit guide

“If you can fit more than two fingers under the band, the band is too large. If you can’t fit two fingers, it’s too small.”

– Miss Mary UK fitting expert

“Research from the University of Portsmouth suggests that up to 80% of women are wearing the wrong bra size, leading to discomfort and back pain.”

– University of Portsmouth study (2010) on bra fit

For UK women shopping online or in‑store, the path to a good fit starts at home with a tape measure. But remember: your measurement is a starting point – the final verdict comes from how the bra looks and feels on your body. Try on at least three sizes in each style (your calculated size, one band up, one band down), and don’t be afraid to use sister sizes. The trade‑off between convenience and precision is real, but with this guide you’ll walk in knowing exactly what to look for.