Bra Size Calculator & Fitting Guide
Enter your underbust and fullbust measurements to instantly find your band size, cup letter and sister sizes.
Measure snugly just below the bust, tight but breathable.
Measure at the fullest point of the bust, keeping the tape parallel to the floor.
⚠️ Results are based on EU/TR standard sizing. Fit varies by brand and style — always check the brand's own size guide before purchasing.
How to Measure Your Bra Size at Home?
You only need two measurements for an accurate bra size: underbust circumference (determines band size) and fullbust circumference (determines cup size). The difference between the two gives you the cup letter. Use a soft (dressmaker's) tape measure for both.
Step 1: Measuring Your Underbust (Band Size)
Wrap the tape measure snugly around your torso just below your bust, parallel to the floor. It should be firm — tight enough to measure accurately but not so tight that it digs in. Round up to the nearest even number (US) or nearest 5 cm (EU/TR) to get your band size. Example: 73 cm → 75 (EU) or 28.7 in → 30 (US).
Band Size (EU) = Underbust (cm) → Round to nearest 5
Step 2: Measuring Your Bust (Cup Size)
Wrap the tape around the fullest part of your bust, keeping it parallel to the floor. Do not pull it tight — let it rest snugly. Leaning slightly forward as you measure helps your breasts fall into their natural position for a more accurate reading.
How is Cup Size Calculated?
Cup size is expressed as a letter derived from the centimeter difference between your fullbust measurement and your band size. Each letter represents roughly a 2 cm increment. The larger the difference, the further along the alphabet the cup letter falls.
The Difference Between Bust and Underbust Measurements
Cup Difference = Fullbust − Band Size (cm)
Example: 94 cm fullbust − 80 cm band = 14 cm difference → D cup → 80D
Understanding A, B, C, D, DD, and Larger Cup Sizes
| Cup Letter | Difference (cm) | Description |
|---|---|---|
| AA | 0–1 cm | Very small volume |
| A | 2–3 cm | Small volume |
| B | 4–5 cm | Small-medium volume |
| C | 6–7 cm | Medium volume |
| D | 8–9 cm | Medium-large volume |
| DD / E | 10–11 cm | Large volume |
| DDD / F | 12–13 cm | Full-figure volume |
| G+ | 14+ cm | Extended sizing / specialty |
What Are Sister Sizes in Bras?
Sister sizes are bra sizes that share the same cup volume but have different band sizes. When you go up one band size, you drop one cup letter — and vice versa — keeping the total cup volume identical. This is useful when your exact size is unavailable or when you fall between sizes.
How to Use the Sister Size Chart (e.g., Switching from 34C to 36B or 32D)
Yes. The sister sizes of 34C are 36B (looser band, one cup smaller) and 32D (tighter band, one cup larger). Cup volume is identical across all three. If the band feels too tight, try 36B; if it's too loose, try 32D. The same logic applies across all sizes.
Sister Size Conversion Table
| Smaller Band Sister | Base Size | Larger Band Sister |
|---|---|---|
| 70C | 75B | 80A |
| 75C | 80B | 85A |
| 75D | 80C | 85B |
| 80D | 85C | 90B |
| 80E | 85D | 90C |
| 85E | 90D | 95C |
Signs You Are Wearing the Wrong Bra Size
Slipping Straps, Riding Up Back Bands, and Cup Spillage (Double Boob Effect)
One or more of the following signs typically indicates an incorrect bra size:
Straps keep slipping off
Band too large → straps doing all the support work
→ Go down a band size, up a cup letter
Band rides up in back
Band too big → pulls upward instead of staying level
→ Go down a band size
Cup spillage / double boob
Cup too small
→ Go up a cup letter
Cups wrinkle or gap
Cup too large
→ Go down a cup letter
Underwire digs in
Band too tight or cup too small
→ Try a sister size (up band + down cup)
Center gore doesn't lie flat
Cup too large or wrong shape for your body
→ Go down a cup letter or try a sister size