Calq.

Bra Size Calculator

Find your perfect fit. Calculate your bra size based on bust and underbust measurements.

Your Measurements

Measure snugly around your ribcage, just under your bust.

Measure around the fullest part of your bust.

Introduction

Calq.’s Bra Size Calculator helps you quickly estimate your bra size from two body measurements. It is designed for anyone buying bras online, checking fit after body changes, or converting between US/UK, EU, FR/ES, AU/NZ, IT, and JP sizing. The goal is a confident starting size; final fit always depends on the specific brand and style.

How it works

  1. Choose units in inches or centimeters.
  2. Measure your underbust (snug, directly under the bust).
  3. Measure your bust (around the fullest part).
  4. Enter your numbers. The calculator returns a US/UK size by default, plus sister sizes and international conversions.
  5. Try the result and, if needed, its sister sizes to fine-tune comfort and support.

Inputs explained

  • Unit system (in or cm): The calculator accepts either and converts if needed. 1 in = 2.54 cm.
  • Underbust measurement: A snug, level measurement under the bust. This drives your band size (the number, e.g., 34).
  • Bust measurement: A comfortable, level measurement over the fullest part of the bust. This drives your cup size (the letter, e.g., C).

Results & interpretation

  • Calculated bra size: Your primary result shown in US/UK sizing (e.g., 34C). This is the starting point to try on.
  • Sister sizes: Sizes that keep the same cup volume but change band tightness.
    • Down a band, up a cup (tighter band): from 34C → 32D.
    • Up a band, down a cup (looser band): from 34C → 36B.
  • International conversions:
    • EU/DE: numeric band such as 70, 75, 80; cups A, B, C, D, E, F, G, H…
    • FR/ES: band equals EU band + 15 (e.g., EU 75 → FR/ES 90); cups A, B, C, D, E, F…
    • AU/NZ: band 6, 8, 10, 12…; cups typically follow UK lettering (including double letters).
    • IT: many labels use EU bands; when Italian 1-6 is shown, it often maps to EU 65-90 (see Method & assumptions).
    • JP: bands 60, 65, 70, 75…; cups use 2.5 cm steps (A, B, C, D, E, F…), so letters may differ from EU/UK for the same volume.

Method & assumptions

  • Band size (US/UK):

    • Band (inches) = underbust rounded to the nearest even number (28, 30, 32, 34, 36, 38, 40…).
    • Bands reflect typical stretch; very compressive sports styles may feel tighter.

  • Cup size (US/UK):

    • Cup difference (inches) = bust − band.
    • Mapping (US/UK reference):
      • 0 in ≈ AA
      • 1 in = A
      • 2 in = B
      • 3 in = C
      • 4 in = D
      • 5 in = UK DD; US often DD or E
      • 6 in = UK E; US often DDD or F
      • 7 in = UK F; US often G
      • 8 in = UK FF; US often H
      • 9 in = UK G; US often I
      • 10 in = UK GG; US often J
      • Higher differences continue in similar steps.

  • Centimeter inputs:

    • We convert to inches to compute US/UK size, then map to other systems.

  • Converting bands between systems (quick reference):

    • UK/US 28 = EU 60 = FR/ES 75 = AU/NZ 6 = JP 60
    • 30 = 65 = 80 = 8 = 65
    • 32 = 70 = 85 = 10 = 70
    • 34 = 75 = 90 = 12 = 75
    • 36 = 80 = 95 = 14 = 80
    • 38 = 85 = 100 = 16 = 85
    • 40 = 90 = 105 = 18 = 90
    • 42 = 95 = 110 = 20 = 95
    • 44 = 100 = 115 = 22 = 100
    • IT note: many Italian brands print EU bands; when 1-6 is used, a common mapping is IT 1=EU 65, 2=70, 3=75, 4=80, 5=85, 6=90.

  • Converting cups:

    • UK double letters to EU single letters:

      • UK D → EU D
      • UK DD → EU E
      • UK E → EU F
      • UK F → EU G
      • UK FF → EU H
      • UK G → EU I
      • UK GG → EU J, and so on.

    • US letters typically align to EU single letters after D:

      • US DD/E → EU E
      • US DDD/F → EU F
      • US G → EU G, H → H, etc.

    • JP cups use 2.5 cm steps (A=10 cm, B=12.5 cm, C=15 cm, D=17.5 cm, E=20 cm, F=22.5 cm…). This often yields a smaller letter for the same cup volume when compared to EU/UK.

  • Assumptions and limitations:

    • Measurements rely on tape placement and posture; minor errors can shift results.
    • Brands, materials, underwire shapes, and styles vary; expect to try adjacent sister sizes.
    • This tool provides general, non-medical guidance.

Health and fit context

A well-fitting bra can improve comfort, posture, and support. Watch for signs of poor fit: the band rides up, the center gore floats, the cups wrinkle or spill, or straps dig in. If you experience pain, skin irritation, or persistent discomfort, consult a professional fitter. This calculator is not medical advice.

Tips & strategies

  • Measure in front of a mirror with a soft tape; keep the tape level and snug.
  • Exhale gently for the underbust; do not hold your breath.
  • Take the bust measurement while standing; if very full or projected, also check a leaning measurement and use the larger value.
  • Round to the nearest 0.5 cm or 0.25 in for consistency.
  • Start with the calculated size, then try sister sizes if the band feels too loose or tight.
  • For sports bras or strapless styles, many people prefer a firmer band or different cup shape.
  • Re-measure after body changes, pregnancy, weight shifts, or new medication affecting fluid retention.

Example calculation

  • Inputs (inches): underbust 31 in, bust 37 in.

  • Band (US/UK): nearest even = 32.

  • Cup difference: 37 − 32 = 5 in.

  • Cups:

    • UK result: 32DD.
    • US result: often labeled 32DD or 32E depending on brand.

  • International conversions:

    • EU: 70E (UK DD maps to EU E).
    • FR/ES: 85E (EU 70 + 15).
    • AU/NZ: 10DD (AU uses UK-style cups).
    • IT: 2E when Italian 1-6 is used; many labels would simply show EU 70E.
    • JP: 70C approximately, because the 15.2 cm bust-underbust difference maps to JP C (2.5 cm steps). This is normal; JP letters do not match EU/UK one-for-one even when volume is similar.

  • Sister sizes to try:

    • Tighter band, larger cup: 30E (UK 30E) or, in US labeling, 30DDD/30F.
    • Looser band, smaller cup: 34D (UK 34D) or US 34D.

Frequently asked questions

  1. Do I still need to “add 4 inches” to my band?

    • No. That older rule comes from non-stretch fabrics. Modern bands stretch; using the snug underbust and rounding to the nearest even band works better for most people.

  2. Why do US and UK cup letters look different after D?

    • The UK uses double letters (DD, FF, GG) while the US often uses single letters (E, F, G) with occasional DD/DDD. Our results show the likely label you will see in each market.

  3. What are sister sizes and how do I use them?

    • Sister sizes keep cup volume constant while the band changes. If the band is too tight, go up a band and down a cup (34C → 36B). If the band is loose, go down a band and up a cup (34C → 32D).

  4. How close will this be to my “perfect” size?

    • It provides a strong starting point. Because cup shapes, wires, and materials vary by brand, expect to try the result and one sister size on either side.

  5. How do I convert an EU size I already know?

    • Use the quick band reference: EU 70 ≈ UK/US 32 ≈ FR/ES 85 ≈ AU/NZ 10 ≈ JP 70. Convert cups using the mapping in Method & assumptions (e.g., UK DD → EU E).

  6. Can my size change during the day?

    • Yes. Hydration, cycle, and posture can shift volume slightly. If you are between sizes, consider the more comfortable option and use sister sizes to adjust.

Summary

The Calq. Bra Size Calculator estimates your band and cup from two measurements, then converts to EU, FR/ES, AU/NZ, IT, and JP and lists sister sizes. Use the result as a starting size, check fit signs, and try the suggested sister sizes to fine-tune. Sizes vary by brand and style, so treat this as guidance rather than a final prescription. Use the calculator above with your details to find your best starting fit today.