Bra Size Calculator
Use this calculator to estimate your bra band and cup size from two measurements: your underbust and fullest bust.
Measure snugly around your ribcage, directly under your bust.
Measure around the fullest part of your bust while standing naturally.
How to Figure Out Bra Size at Home
Finding the right bra size can feel confusing because brands vary, body shape varies, and even measurement methods vary. That said, a simple two-measurement system gives a strong starting point. This page helps you estimate size quickly and understand what to adjust if the fit still feels off.
The calculator above gives you an estimated US/UK bra size, plus a rough EU band equivalent. Think of the result as your baseline size, not the final answer for every bra style.
Step-by-Step Measuring Guide
1) Measure your underbust
- Use a soft measuring tape.
- Wrap it around your ribcage directly under your bust.
- Keep the tape level and snug (not painfully tight).
- Breathe out gently, then read the number.
2) Measure your full bust
- Wrap the tape around the fullest part of your bust.
- Keep tape horizontal across your back.
- Do not pull too tight—just lightly touching the body.
- Record the number.
3) Let the calculator estimate your size
The band size comes from your underbust and is rounded to a standard even number. Cup size comes from the difference between bust and underbust measurements.
Quick Cup Difference Guide (Approximate)
| Bust - Underbust Difference | Estimated Cup |
|---|---|
| 0 to 0.5 in | AA |
| ~1 in | A |
| ~2 in | B |
| ~3 in | C |
| ~4 in | D |
| ~5 in | DD / E |
| ~6 in | DDD / F |
| ~7 in | G |
| ~8 in | H |
Common Fit Issues (And What to Change)
Band rides up in the back
Your band is probably too loose. Try one band size down (for example, from 36C to 34D).
Straps dig into shoulders
Often the band is not providing enough support. Tighten the band or try a smaller band/larger cup combination.
Cups gap at the top
You may need a smaller cup, or a different cup shape (balconette vs. full coverage can fit very differently).
Spillage at the top or sides
Cup is likely too small. Try one cup up first while keeping band the same.
What Are Sister Sizes?
Sister sizes are different bra sizes with similar cup volume. If a band feels tight but cups fit, go up a band and down a cup. If the band feels loose, go down a band and up a cup.
- Example: 34C sister sizes are 32D and 36B.
- Use sister sizes when a specific model runs tight or loose.
Important Notes Before You Buy
- Different brands and styles fit differently even in the same size.
- Sports bras, plunge bras, and bralettes may size differently.
- Body changes over time, so re-measure every 6-12 months.
- If possible, test movement: raise arms, bend, and walk around.
Final Thoughts
A bra size calculator is the best first step when you want a fast, practical estimate. Use the number as a foundation, then fine-tune based on real-world fit and comfort. The goal is not just a label—it is support, comfort, and confidence throughout your day.