# Bra Size Calculator

Calculate your bra size from band and bust measurements. Supports US, UK, and EU sizing with sister size recommendations for the perfect fit.

## What this calculates

Find your correct bra size with two simple measurements. Measure your underbust (band) and bust circumference, and this calculator determines your band size, cup size, and sister sizes in US, UK, or EU sizing systems. An estimated 80% of women wear the wrong bra size.

## Inputs

- **Band Measurement (Underbust)** (inches) — min 24, max 56 — Measure snugly around ribcage, directly under the bust
- **Bust Measurement** (inches) — min 26, max 64 — Measure around the fullest part of the bust, loosely
- **Sizing System** — options: US / North America, UK, EU / Continental

## Outputs

- **Your Bra Size** — formatted as text
- **Band Size**
- **Cup Size** — formatted as text
- **Sister Size (band up)** — formatted as text — Same cup volume, larger band
- **Sister Size (band down)** — formatted as text — Same cup volume, smaller band

## Details

How to measure:

  - Band (underbust): Wrap a tape measure snugly around your ribcage, directly under your bust. Keep it level and breathe normally.

  - Bust: Measure around the fullest part of your bust. Do not compress. Keep the tape level.

The cup size is determined by the difference between bust and band:

  - 0" = AA | 1" = A | 2" = B | 3" = C | 4" = D | 5" = DD | 6" = DDD/F

Sister sizes have the same cup volume but different band sizes. Going up a band size means going down a cup letter, and vice versa.

## Frequently Asked Questions

**Q: What are sister sizes?**

A: Sister sizes are bra sizes with the same cup volume but different band sizes. For example, 34C, 36B, and 32D are all sister sizes with the same cup volume. If your usual size feels off, try a sister size: band too tight = go up a band and down a cup, band too loose = go down a band and up a cup.

**Q: Why do bra sizes vary between brands?**

A: Like clothing, bra sizing is not standardized. Different brands use different patterns, materials, and stretch properties. A 34C in one brand may fit like a 36B in another. Always try on bras when possible, and do not be attached to a specific size number.

**Q: How do I know if my bra fits correctly?**

A: A well-fitting bra has: a band that sits level and snug (you can fit 2 fingers under it), cups that fully contain breast tissue without gapping or spillover, straps that stay in place without digging in, and a center gore that lies flat against the sternum.

**Q: How often should I get re-measured?**

A: Bra size can change due to weight fluctuations, hormonal changes, aging, pregnancy, and exercise. Re-measure every 6-12 months, or whenever your current bras feel uncomfortable. Most women's bra size changes multiple times throughout their life.

**Q: How do I convert between US, UK, and EU sizes?**

A: Band sizes convert roughly as: US/UK 32 = EU 70, US/UK 34 = EU 75, US/UK 36 = EU 80. Cup sizes differ after D: US DD = UK DD, US DDD = UK E, US G = UK F. This calculator handles conversions automatically.

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Source: https://vastcalc.com/calculators/everyday/bra-size
Category: Everyday Life
Last updated: 2026-04-21