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Bra Size Calculator

Use this bra size calculator to review an educational health calculation for bra size.

Primary answer
Estimated bra size
Inputs to verify
Underbust measurement, Bust measurement, and Measurement unit
Use type
Use as an estimate that depends on assumptions.
Keyword intent
bra size calculator

Calculator

Bra Size Calculator

Calculates estimated bra size from underbust measurement, bust measurement, measurement unit. Defaults are filled in so you can review a working example before changing inputs.

in or cm

Measure around the body just beneath the breasts.

in or cm

Measure around the fullest part of the bust.

Choose inches or centimeters for both measurements.

Result

Result reflects the current submitted inputs.

  • Risk B
  • Reviewed 2026-05-26
  • 2 sources
Estimated bra size34C
Band size34 in
Cup sizeC
Cup difference2 in
Sister sizes32D / 36B
Fit noteTreat this as a starting size only; bra sizes can vary by brand, style, fabric, and fit preference.

Breakdown

Underbust used
30 in
Bust used
36 in
Rounded underbust
30 in
  • This calculator estimates a starting UK-style size; it does not guarantee fit.
  • Bra sizing varies by brand, style, materials, and measurement method.
  • Centimeter inputs are converted to inches using 2.54 cm per inch.
  • Cup labels outside the source chart are rejected rather than invented.

Accuracy notes

Risk level
B
Reviewed
2026-05-26
Sources
2
Primary result
Estimated bra size

Formula logic is kept in a pure calculator module with fixtures, source notes, and page-visible assumptions.

Categories

What the result means

Estimated bra size answers the page's main bra size question. UK-style starting bra size based on the selected measurement method. Treat the result as educational context, then read the limitations and assumptions before discussing it with a professional. Use band size, cup size, and cup difference to explain why estimated bra size moved when an input changed. Record the inputs you used and verify any health concern with a qualified professional.

Estimated bra sizeUK-style starting bra size based on the selected measurement method.
Band sizeTraditional plus-four band estimate.
Cup sizeCup label from the source-backed difference chart.
Cup differenceRounded bust minus band difference used for cup lookup.

Use the result this way

  1. Start with Estimated bra size, then use supporting outputs only to explain the primary answer.
  2. Verify underbust measurement, bust measurement, and measurement unit before copying the result.
  3. Choose the mode or method first because it can change which formula is applied, keep units consistent with the labels shown in the form, and stay within the documented minimum and maximum ranges.
  4. Record the inputs you used and verify any health concern with a qualified professional.

User job

How to use this calculator

Use Bra Size Calculator when you need estimated bra size, then use band size and cup size to check the context for general wellness education and preparing for a professional conversation.

Best for

  • Understanding a formula-based estimate
  • Seeing which inputs drive a health-related output
  • Reviewing a default example before entering your own underbust measurement and bust measurement.

Check before relying

  • Health formulas can be population-specific; do not use the result as diagnosis or treatment advice.
  • This calculator estimates a starting UK-style size; it does not guarantee fit.
  • Bra sizing varies by brand, style, materials, and measurement method.
  • Source context: Breast Cancer Now, reviewed 2026-05-26.

Next useful step

  • Body Type CalculatorUse next when you need apparel body type from bust circumference and waist circumference after checking estimated bra size.
  • BMR CalculatorUse next when you need estimated BMR from age and sex used by equation after checking estimated bra size.
  • Body Fat CalculatorUse next when you need estimated body fat from age and sex used by equation after checking estimated bra size.

Formula

Uses a source-backed traditional plus-four band estimate and UK-style cup difference chart. Key assumptions: This calculator estimates a starting UK-style size; it does not guarantee fit. Bra sizing varies by brand, style, materials, and measurement method. Centimeter inputs are converted to inches using 2.54 cm per inch.

  • Uses a source-backed traditional plus-four band estimate and UK-style cup difference chart.
  • This calculator estimates a starting UK-style size; it does not guarantee fit.
  • Bra sizing varies by brand, style, materials, and measurement method.
  • Primary source context: Breast Cancer Now.

Inputs

Enter underbust measurement, bust measurement, and measurement unit for general wellness education and preparation for a professional conversation. Before calculating, choose the mode or method first because it can change which formula is applied, keep units consistent with the labels shown in the form, and stay within the documented minimum and maximum ranges. Underbust measurement: Measure around the body just beneath the breasts. Bust measurement: Measure around the fullest part of the bust. Measurement unit: Choose inches or centimeters for both measurements.

Underbust measurementMeasure around the body just beneath the breasts.
Bust measurementMeasure around the fullest part of the bust.
Measurement unitChoose inches or centimeters for both measurements.

Example

Using the default inputs, Bra Size Calculator returns estimated bra size of 34C. Adjust underbust measurement, bust measurement, and measurement unit to match your own scenario.

FAQ

How is estimated bra size calculated here?

Uses a source-backed traditional plus-four band estimate and UK-style cup difference chart. The first assumption to check is: This calculator estimates a starting UK-style size; it does not guarantee fit.

What does Estimated bra size mean for bra size?

Treat the result as educational context, then read the limitations and assumptions before discussing it with a professional. Secondary values such as band size, cup size, and cup difference are there to explain the primary answer, not to replace it.

What should I enter for Underbust measurement?

Measure around the body just beneath the breasts. Use in or cm for this field. Choose the mode or method first because it can change which formula is applied, keep units consistent with the labels shown in the form, and stay within the documented minimum and maximum ranges.

How does Bust measurement change estimated bra size?

Measure around the fullest part of the bust. Changing it can alter estimated bra size because the formula uses the submitted inputs together. Also compare measurement method, formula population, age range, units, sex or activity assumptions, and clinical context.

Why does the bra size example show 34C for estimated bra size?

The default inputs produce 34C for estimated bra size. Treat that as a format and scale check, then replace every default value with your own inputs.

Can the bra size result diagnose or prescribe anything?

No. Use it as educational context only. Health formulas can depend on population, measurement method, age range, and clinical context.

Sources

Last reviewed: 2026-05-26

  • Reviewed 2026-05-26
    SourceBreast Cancer Now. Source for plus-four/plus-five band method, cup-difference chart, example, and fit caveat.
    Scope
    Source for plus-four/plus-five band method, cup-difference chart, example, and fit caveat.
    Limits
    Guide-based starting estimate; not brand-specific and not a substitute for a professional fitting, especially after breast surgery.
  • Reviewed 2026-05-26
    SourceNational Institute of Standards and Technology. Source for bra-size measurement context and the limitation that cup and band labels are not standardized across manufacturers and styles.
    Scope
    Source for bra-size measurement context and the limitation that cup and band labels are not standardized across manufacturers and styles.
    Limits
    NIST report is about armor testing surrogates, not consumer fitting advice; used only for measurement and standardization caveats.

Disclaimer

This health calculator is for educational estimates only. It does not diagnose, treat, or replace advice from a qualified health professional.