Bra Size Calculator

Calculated using standard mathematical and industry formulas.

Free online Bra Size Calculator calculator and unit conversion tool for everyday, engineering, and home projects.

How to use this calculator?

1. Measure underbust & bust.
2. Select sizing method.
3. Read band, cup, and sister sizes.

Formula & calculation method

Band & Cup Method

Cup = Index(Bust - Band)

Modern fitting rules.

Step-by-step calculation example

30 in underbust + 34 in bust = 30D.

Key insights to remember

• 1 inch bust-band difference = 1 cup size.

How to interpret your results?

Sister Sizes

Equivalent cup volume on different bands.

Frequently asked questions

How do I use the Bra Size Calculator calculator?

Enter your numerical input and select desired units to get instant accurate results.

How accurate are the conversions?

Conversions use official ISO conversion factors for maximum precision.

Does it convert metric and imperial units?

Yes, seamless conversions between metric (meters, kg) and imperial (feet, lbs) are supported.

Is my data stored?

No, all calculations execute 100% locally in your browser with zero data logging.

Can I use this for DIY or engineering projects?

Yes, it provides reliable estimates for construction, crafting, science, and everyday math.

What if I enter invalid inputs?

The calculator will display a friendly error prompt if non-numeric values are entered.

Related calculators

• Height Calculator — Convert cm to feet/inches or predict child adult height.
• Shoe Size Calculator — Convert shoe sizes between US, UK, EU, Japan (cm), and foot length.

See all other calculators · Explore all online calculators