best bra size calculator

How this best bra size calculator works

A great bra fit starts with two measurements: your underbust (for band size) and your fullest bust measurement (for cup size). This best bra size calculator uses those two numbers to estimate your size in a simple, practical way. The result is designed to help you begin shopping confidently, then fine-tune based on comfort and brand differences.

The calculator rounds your underbust to the nearest even band size, then compares the bust measurement to that band. The inch difference determines cup volume (A, B, C, D, DD, and so on). If your measurements are in centimeters, they’re converted automatically.

How to measure correctly

1) Snug underbust

Wrap your measuring tape directly under your bust, where the bra band sits. Keep it snug—not painfully tight—and level all the way around. Exhale naturally before reading the number.

2) Fullest bust

Measure around the fullest part of your bust while standing upright. Keep the tape relaxed and straight. Avoid pulling too tight, since that can underestimate cup size.

3) Enter and calculate

Enter both values above, choose your measurement unit, and click Calculate Size. You’ll get:

• Your estimated bra size
• Your band and cup breakdown
• Nearby sister sizes for better fit flexibility

Understanding band size vs cup size

Cup letters are not absolute. A D cup on a 32 band is much smaller in volume than a D cup on a 40 band. That’s why bra sizes are always interpreted as a pair, such as 34C or 38DD.

• Band size provides most of the support (usually about 80–90%).
• Cup size is based on the difference between bust and band.
• Sister sizes keep similar cup volume while changing band tightness.

Common fit checks after using a calculator

Signs your band is too loose

• The back rides up during the day.
• You can pull the band far away from your body.
• Straps are doing too much of the support work.

Signs your cup may be too small

• Spillage at the top or sides of the cups.
• Center gore (middle panel) does not sit flat.
• Underwire rests on breast tissue.

Signs your cup may be too large

• Wrinkling or gaping in the cup fabric.
• Shifting when you move.
• Straps over-tightened to compensate.

What are sister sizes?

Sister sizes are alternate sizes with similar cup volume. If your calculated size feels almost right, try one of the sister sizes:

• Go down one band and up one cup (e.g., 34C → 32D)
• Go up one band and down one cup (e.g., 34C → 36B)

This is especially useful when one brand’s band runs tight or loose compared with another.

Best practices for long-term comfort

• Re-measure every 6–12 months or after major body changes.
• Rotate between bras to preserve elasticity.
• Start on the loosest hook for a new bra so you can tighten later as it stretches.
• Prioritize comfort and support over the label alone.

Final thoughts

The best bra size calculator is the one that gives you a reliable starting point and helps you make better fitting choices quickly. Use your result, test the fit signs above, and try sister sizes when needed. A comfortable bra should feel supportive, stable, and almost unnoticeable during daily wear.