SamCalculator

Bra Size Calculator

Find your accurate bra size using bust and band measurements, compare international sizing systems, convert bra sizes worldwide, and discover the perfect fit.

Measurements

Fullest part
in
Snug, below breasts
in

Advanced Fitting Mode

Add loose, snug & tight underbust + 3-position bust measurements for improved accuracy

Measurement Guide

1Bust — fullest point2Underbust — snug fit① − ② = Cup Difference1" = A · 2" = B · 3" = C · 4" = D · 5" = DD

How to Measure

  1. 1

    Bust measurement

    Wrap the tape around the fullest part of your bust (nipple line). Keep it parallel to the floor, snug but not tight.

  2. 2

    Underbust measurement

    Wrap the tape snugly just below the breasts where the band sits. Exhale and read the number — firm but breathable.

Quick Reference

1" diffCup A
2" diffCup B
3" diffCup C
4" diffCup D
5" diffCup DD
6" diffCup DDD

Measure without a padded bra or braless for the most accurate result.

How Bra Sizing Works

A bra size is expressed as a band number (your underbust circumference, in inches in the US/UK or cm in Europe) plus a cup letter (the difference between your bust and underbust measurements). The band provides approximately 80% of the support; the cup determines volume. For example, a 34C has the same cup volume as a 32D or a 36B — these are called sister sizes.

How the Calculator Works

Step 1 — Measure

Use a soft measuring tape. Measure your underbust snugly just below the breasts (where the bra band sits). Then measure the bust at its fullest point, usually at nipple level, with the tape parallel to the floor.

Step 2 — Calculate Band

Round your snug underbust measurement to the nearest even number — this is your US/UK band size. In Europe, the band is the underbust in cm, rounded to the nearest 5 (e.g. 82 cm → EU 80).

Step 3 — Calculate Cup

Subtract underbust from bust. Each inch of difference corresponds to one cup size: 1" = A, 2" = B, 3" = C, 4" = D, 5" = DD, 6" = DDD/F, and so on. In cm: 2.5 cm per cup size.

Step 4 — Convert & Fit

Use the converter tab to express your size in any regional system. Remember that cup letters mean different things in different countries — a UK F is not the same as a US F. Always verify sizing by trying on the bra.

6 Ways to Use This Tool

1

Find Your First Size

Calculate your bra size from scratch using the Size Calculator tab. Enter bust and underbust for an instant result with international equivalents.

2

Shop Internationally

Use the Size Converter to translate your home size before buying from UK, European, Japanese, or Australian brands online.

3

Find Alternative Fits

Use Sister Sizes when your exact size is out of stock. The same cup volume comes in several band/cup combinations.

4

Diagnose Fit Problems

Use the Fit Guide to identify whether discomfort comes from the band, cup, straps, or style — and get specific correction advice.

5

Shop for Special Occasions

Understanding your size helps you choose the right strapless, sports, maternity, or nursing bra with confidence.

6

Track Size Changes

Re-measure seasonally. Weight changes of 5–10 lbs, pregnancy, breastfeeding, and age regularly shift band and cup size.

Bra Sizing Best Practices

  • Measure yourself without wearing a bra (or in a non-padded, unlined bra) for the most accurate bust measurement.
  • Keep the measuring tape parallel to the floor all the way around — even a slight angle changes the number.
  • Take your underbust measurement on an exhale when the tape is snug but not constricting — you should be able to breathe comfortably.
  • Measure the bust at the nipple line for most body types. For fuller busts, lean forward 90° while measuring (the 'leaning method') for a more accurate cup reading.
  • Always start a new bra on the loosest hook — as the elastic stretches over time, you can tighten to the next hooks to maintain support.
  • Replace bras every 6–12 months with regular wear. Elastic, underwires, and fabric degrade and reduce support significantly after 6 months of frequent washing.

Why Getting Your Size Right Matters

Research published in the journal Chiropractic & Manual Therapies found that up to 80% of women wear an incorrectly sized bra. The consequences extend beyond discomfort: an ill-fitting bra can contribute to neck pain, back pain, shoulder grooving, skin abrasion, restricted breathing, and poor posture. Conversely, a correctly fitted bra provides lift, support, and silhouette definition that affects how clothing drapes and fits.

For women with larger busts (D cup and above), proper support can meaningfully reduce exercise-related breast pain (mastalgia). A study in the British Journal of Sports Medicine found that breasts can move up to 21 cm vertically during exercise, with a correctly fitted sports bra reducing movement by 74%.

Tricky Sizing Situations

Different left and right breast sizes

Always size to the larger breast. Use a removable insert on the smaller side to even out silhouette. A slight difference of 0.5–1 cup size is common and normal.

Post-mastectomy or reconstruction

Mastectomy bras have pockets for prosthetics. Measure the existing breast normally; the prosthetic should match the volume of the removed breast.

Ribs and back width mismatch

A wide rib cage with a smaller frame may need the European sizing method (snug underbust in cm ÷ 2) or plus-size band fittings.

Brand-to-brand variation

Cup volume varies by brand (a UK bra labeled 34C may differ from a US 34C by half a cup). Always check the brand's specific size chart and read fit reviews.

Core Bra Sizing Formulas

US/UK Band SizeBand = round(underbust in inches) → nearest even number
Cup DifferenceCup diff = bust (in) − underbust (in)
Cup IndexA=1", B=2", C=3", D=4", DD=5", DDD/F=6", G=7", H=8"…
EU BandEU Band = underbust (cm) → rounded to nearest 5 cm
France BandFR Band = EU Band + 15 (e.g. EU 70 → FR 85)
Sister SizeBand ±2" & Cup ∓1 letter (same cup volume)

Common Bra Fitting Mistakes

Adding inches to underbust

The old '+4 inch' rule (e.g. 32" underbust → 36" band) was invented when bras had no stretch. Modern bras use elastic — use your actual snug underbust measurement for your band size.

Measuring over a padded bra

Foam padding adds up to 2 inches to your bust measurement. Measure without a bra or in an unpadded, unlined bra for accuracy.

Ignoring cup letter differences by country

A UK F equals a US DDD/F. A US G equals a UK F — not the same. Always use a size conversion chart when buying internationally.

Buying based on size alone

Different brands cut bras differently. Two 34C bras from different brands can vary by a full cup in actual volume. Try on or check brand-specific fit guides.

About This Calculator

The SamCalculator Bra Size Calculator uses the modern fitting method endorsed by professional bra fitters worldwide: band size equals snug underbust rounded to the nearest even number, and cup size equals the difference between bust and underbust. Band and cup conversions use published international sizing standards. This tool is for informational and guidance purposes; individual brand sizing, body shape, and fabric stretch will all affect your ideal size. When in doubt, visit a professional bra fitter for an in-person assessment.

Frequently Asked Questions

You need a soft measuring tape. First, measure your underbust: wrap the tape snugly just below your breasts, where the bra band sits. Keep it parallel to the floor and exhale before reading. Second, measure your bust: wrap the tape around the fullest part of your breasts (usually at nipple level), keeping it parallel to the floor. Enter both measurements into the calculator above to get your band size, cup size, and international equivalents instantly.

The band size is the number in a bra size (e.g. the 34 in 34C). It represents the circumference of your ribcage just below the bust. In US and UK sizing, band sizes are even numbers in inches (28, 30, 32, 34, 36, 38, 40, 42, 44, 46, 48). In European sizing, the band is measured in centimeters and rounded to the nearest 5 cm (EU 70, 75, 80, 85, etc.). The band provides approximately 80% of the support a bra gives.

Cup size is the letter in a bra size (e.g. the C in 34C). It represents the difference between your bust and underbust measurements. In US/UK sizing: AA = <1 inch, A = 1 inch, B = 2 inches, C = 3 inches, D = 4 inches, DD = 5 inches, DDD/F = 6 inches, G = 7 inches, H = 8 inches, and so on. Cup letters are not universal — a UK F equals a US DDD. Cup size only represents volume relative to the band, so 32D and 34C have the same cup volume.

Sister sizes are alternative bra sizes that enclose the same cup volume as your primary size but with a different band and cup letter. When you go down one band size, you go up one cup letter (and vice versa). For example, 34C = 32D = 36B — all have the same cup volume. Use sister sizes when your exact size is sold out, when traveling internationally, or when a brand's band runs looser or tighter than expected.

A calculator based on proper measurements (snug underbust for band, fullest bust for cup) is accurate for most body types. Studies show that bra size calculators using the modern method (no +4 inch addition) are more accurate than the old traditional method. However, cup shape, breast projection, tissue density, and brand variations all affect real-world fit. Treat calculator results as a starting point, then adjust based on how the bra actually feels.

Measure every 6–12 months, and whenever you experience significant weight change (5–10 lbs in either direction), pregnancy, post-pregnancy weight change, or start breastfeeding. Bra size also commonly changes at menopause due to hormonal shifts affecting breast tissue density. Many women find their size changes several times throughout their adult life — keeping measurements current ensures proper support and comfort.

US and UK bra bands use the same inch-based measurements, so US 34 = UK 34. Cup letters are identical through D and DD, but diverge beyond that: US DDD or F = UK E; US G = UK F; US H = UK FF; US I = UK G; US J = UK GG. This means a US 34G bra is equivalent to a UK 34F, not a UK 34G. Always use a conversion chart when buying from UK brands like Freya, Panache, Curvy Kate, or Boux Avenue.

European bra sizes use centimeters for the band instead of inches. The EU band equals your underbust in cm, rounded to the nearest 5 cm. For example, a 32" band (≈81 cm) rounds to EU 80. EU cups use single letters without repeating (no DD — goes straight from D to E to F to G), equivalent to the US pattern. French sizing adds 15 to the EU band (EU 70 = FR 85, EU 75 = FR 90).

Bra sizing is not standardized between manufacturers. A 34C from Victoria's Secret may differ significantly from a 34C from Panache, Wacoal, or ThirdLove in actual volume, band stretch, cup shape, and wire width. Different factories, materials, and target demographics cause these variations. Always check each brand's size guide, read fit reviews, and if buying a new brand, consider ordering two adjacent sizes to compare.

No — the old '+4 inch' addition rule is outdated. It was developed when bras were made from non-stretch fabrics in the 1950s. Modern bras use elastic fabric that provides adequate comfort and stretch without adding extra inches. Using your actual snug underbust measurement as your band size gives a more supportive and accurate fit. Adding 4 inches typically results in a loose band and too-small cup, which is the most common fitting mistake.

In US sizing, cups D and above are generally considered 'full bust' sizing, with DD, DDD/F, G, H, I, J, K, L, and M representing progressively larger cup volumes. Cup volume is always relative to band size — a 32D cup is considerably smaller in absolute volume than a 42D cup. About 22% of women in the UK wear a cup size FF (US G) or larger, according to market data from specialist lingerie retailers.

Yes. Breast tissue can increase by up to a full cup size during the premenstrual phase due to hormonal changes causing water retention and tissue swelling. Many women find their bra feels tighter in the days before their period. If you're sizing yourself for everyday wear, measure mid-cycle (around days 7–14) for the most representative measurement.

First, calculate your accurate size using this tool. Second, check the brand's specific size guide — not all brands use identical measurements. Third, look for brands offering free returns to facilitate trying multiple sizes. Fourth, search for reviews mentioning 'runs small/large in band' or 'runs large in cup.' Fifth, consider ordering your calculated size and one sister size (e.g., 34C and 32D) to compare. Many specialty lingerie brands also offer virtual fitting consultations.

The most commonly sold bra size in the US is 34B, though this reflects what is most widely manufactured and stocked rather than the actual average. Industry surveys and fitting data from specialist retailers suggest the true statistical average may be closer to 34C or 34D. The UK retailer Bravissimo, which specialises in larger cup sizes, reports its most common size is approximately 30FF–34F, suggesting significant under-measurement among women who default to mainstream sizing.

Yes. Wearing the wrong bra size can cause neck pain, back pain, shoulder grooving from straps bearing too much weight, skin irritation under wires, restricted breathing from a tight band, and reduced posture. A study in the journal Chiropractic & Manual Therapies found that up to 80% of women wear incorrectly sized bras. For larger cup sizes, proper support is especially important to prevent Cooper's ligament stretching, which contributes to long-term breast ptosis (sagging).

For high-impact activities (running, HIIT, aerobics), choose a sports bra in the same cup size as your regular bra but in a band 1–2 sizes smaller — the extra firmness prevents the 21 cm of vertical movement research shows is possible without support. Replace high-impact sports bras every 6–12 months, or when elasticity noticeably declines. For low-impact activities (yoga, walking, Pilates), a medium-support style in your normal size is adequate.

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