Bra Size Calculator - Accurate 6-Point Fitting & Sister Sizes
Accurate 6-point bra size calculator based on orthopedic and lingerie fitting standards. Measures loose, snug, and tight underbust alongside standing, leaning, and lying bust circumferences to calculate true band and cup sizes across US, UK, EU, French, and Australian systems with sister sizes.
Precision 6-Point Bra Measurements
Underbust Measurements
Bust Circumference Measurements
32DDD (F)
Bust / Underbust differential: 5.5" (Calculated on 6-point multi-posture fit)
Sister Sizes (Equal Cup Volume with Alternative Band Fit)
If the band feels too tight: Try 34DD (E). If the band rides up in the back: Try 30G.
Engineering Specifications & Sizing Guide: Bra Size Calculator - Accurate 6-Point Fitting & Sister Sizes
The Bra Size Calculator - Accurate 6-Point Fitting & Sister Sizes provides standards-compliant calculations based on the National Electrical Code (NEC) and EnergyStar HVAC load equations.
Technical Standards & Physics Principles
Electrical and thermal calculations rely on fundamental physical laws—including Ohm's Law (V = I·R) and thermodynamic heat transfer rates. Proper sizing guarantees safe operation, prevents premature equipment failure, and minimizes ongoing utility expenses.
Always apply standard safety allowances (such as maintaining voltage drop under 3% for branch circuits and sizing cooling BTUs to match room solar gain and insulation levels).
Step-by-Step Instructions
Measure Snug Underbust (Band Size)
Wrap a soft measuring tape snugly directly beneath your bust where the bra band sits, keeping the tape level and parallel to the floor.
Measure Fullest Bust (Standing & Leaning)
Measure around the fullest part of your bust (across the nipples) while wearing an unpadded bra, taking standing and leaning measurements for accuracy.
Calculate Cup Size Difference
The calculator computes the difference between bust measurement and band size (`Cup Size = Bust - Snug Underbust`).
Review Sister Sizes & International Conversions
Inspect your primary bra size, sister sizes (alternative band/cup volume equivalents), and international size conversions (US, UK, EU, AU/NZ, France).
Key Features & Capabilities
- Modern ABraThatFits-standard algorithmic measurement method utilizing exact snug underbust and bust dimensional differences
- Sister Size recommendation engine: identifies equivalent cup volume alternatives when bands feel too tight or loose
- Universal international bra size converter: US, UK, European (EU), Australian (AU/NZ), and French (FR) sizing systems
- Cup size progression from AA, A, B, C, D, DD/E, DDD/F, G, H, I, J, to K+
- Fit diagnostic guide troubleshooting common bra issues (spilling cups, riding up band, digging shoulder straps)
- 100% private in-browser calculation with zero data storage
Frequently Asked Questions
How is bra cup size determined from bust and band measurements?
Cup size is determined by the numerical difference in inches between the fullest bust measurement and the snug underbust band size: `1" difference = A Cup`, `2" difference = B Cup`, `3" difference = C Cup`, `4" difference = D Cup`, `5" difference = DD / E Cup`, `6" difference = DDD / F Cup`, `7" difference = G Cup`, and so on.
What are 'Sister Sizes' in bra fitting?
Sister sizes are bra sizes that hold the exact same cup volume despite having different band sizes. If a band is too loose, you go down one band size and up one cup size. For example, **34C** has the exact same cup volume as **32D** (tighter band) and **36B** (looser band).
Why is the old '+4 method' for band sizing inaccurate?
The traditional '+4 method' (adding 4 inches to your underbust measurement to find band size) was created decades ago when bra fabrics were non-elastic. Modern bras use elastic spandex; adding 4 inches results in a band that is too loose to support breast weight, forcing shoulder straps to dig in painfully.
What are the main differences between US and UK bra cup sizing?
US and UK sizing are identical from cups A through D. Beyond D, UK sizing uses double letters (D, DD, E, F, FF, G, GG, H, HH), whereas US sizing uses single progression (D, DD/E, DDD/F, G, H, I, J). A UK 32GG equals a US 32J.
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