best bra calculator

How this best bra calculator works

This calculator uses a modern, practical fitting approach: it estimates your band size from your underbust measurement, then estimates your cup size from the difference between full bust and band. The result is a strong starting point for shopping online or in-store.

Because bra sizing differs by brand and style, your final best fit may be one size up or down. Think of the calculator result as your first fitting target, not a final verdict.

Step-by-step measuring guide

1) Measure your underbust

Wrap a soft tape measure directly under your bust. Keep it straight around your body and pull snug (not painfully tight). Record the number.

2) Measure your full bust

Measure around the fullest point of your bust while standing naturally. Keep the tape level and relaxed. Record the number.

3) Enter your numbers

Select inches or centimeters, enter both values, and click Calculate Size. The tool returns your suggested size and nearby sister sizes.

Understanding band and cup size

A bra size combines two parts:

• Band size (number): around your ribcage, like 30, 32, 34, 36.
• Cup size (letter): based on bust-to-band difference, like A, B, C, D, DD, and beyond.

Important: cup letters are not absolute. A 34D and 38D do not have the same cup volume. Cup volume changes with band size.

What are sister sizes?

Sister sizes keep similar cup volume while changing the band. For example:

• If your band feels tight: go up one band and down one cup (e.g., 34C → 36B).
• If your band feels loose: go down one band and up one cup (e.g., 34C → 32D).

This is the fastest way to fine-tune fit when one part feels right and the other does not.

Common fit issues and quick fixes

Band rides up in back

Your band is likely too loose. Try a smaller band (or tighter hook setting if the bra is new).

Cups gape at the top

You may need a smaller cup, a different cup shape, or a style with less upper-cup coverage.

Spillage over the cup edge

Try a larger cup size or a fuller-coverage cup style for better containment and comfort.

Straps dig into shoulders

Most support should come from the band, not straps. Consider a firmer band fit and better side support.

Best practices for accurate results

• Measure without bulky clothing.
• Use a soft sewing tape, not a rigid ruler.
• Take each measurement twice and average if needed.
• Re-measure every 6–12 months, or after major body changes.

Final note

The best bra calculator gives a solid baseline, but comfort, breast shape, wire width, and fabric stretch all matter. Use your result to shortlist sizes, then test fit with a couple of neighboring options for your true best match.