Studies show that up to 80% of people wear the wrong bra size. The most common mistake? Wearing a band that's too large and a cup that's too small. Here's how to measure yourself accurately at home with just a soft tape measure.
What You Need
Before you start, gather:
- Soft measuring tape — the flexible fabric or vinyl kind used for sewing. A rigid metal tape measure won't conform to your body and will give inaccurate readings.
- A non-padded bra — wear a lightly-padded or unlined bra during measurement, not a push-up. Heavy padding adds false inches to your bust measurement.
- A mirror — optional, but helpful to check that the tape is level in the back.
Do not measure over a shirt or thick clothing. Measure in the morning before eating if possible, as your size can vary slightly throughout the day.
Step 1: Measure Your Band Size
Wrap the tape measure around your ribcage directly under your bust — not around breast tissue. The tape should be snug but not tight; you should be able to breathe normally. Keep the tape parallel to the floor.
Round to the nearest even number:
- If you measure 29 inches → round to 30
- If you measure 30 inches → band size is 30
- If you measure 31 inches → round to 32
- If you measure 32.5 inches → round to 32
US band sizes come in even numbers: 28, 30, 32, 34, 36, 38, 40, 42. If you measure 33 or 35, you're between sizes — start with the smaller even number and check comfort.
Step 2: Measure Your Bust Size
Lean forward at a 90-degree angle before measuring. This lets gravity pull breast tissue naturally forward, which gives a more accurate fullest-point measurement than standing upright.
Wrap the tape loosely around the fullest part of your bust — typically across the nipple line. Keep the tape parallel to the floor and do not compress the tissue. The tape should lay flat without digging in.
Note the measurement in inches. Round to the nearest whole number.
Common mistake: Many people pull the tape too tight here, which underestimates their cup size and leads to the most common fit error — a cup that's too small.
Step 3: Calculate Your Cup Size
Subtract your band measurement from your bust measurement. The difference in inches corresponds to your cup size:
| Difference | Cup Size |
|---|---|
| 0 inches | AA |
| 1 inch | A |
| 2 inches | B |
| 3 inches | C |
| 4 inches | D |
| 5 inches | DD / E |
| 6 inches | DDD / F |
| 7 inches | G |
| 8 inches | H |
Example: Band measurement = 32 inches. Bust measurement = 36 inches. Difference = 4 inches → Cup size D. Your starting size is 32D.
Enter these measurements into the Bra Size Calculator to see your size in US, UK, EU, and Australian sizing systems simultaneously.
Understanding Sister Sizes
Sister sizes are bra sizes with identical cup volume but different band sizes. When you change the band by one size, you change the cup letter by one in the opposite direction to maintain the same cup volume.
| Smaller Band | Your Size | Larger Band |
|---|---|---|
| 30E | 32D | 34C |
| 32E | 34D | 36C |
| 34E | 36D | 38C |
| 30D | 32C | 34B |
| 32D | 34C | 36B |
When to try a sister size:
- Band rides up in back → Go down a band size and up a cup: 34C → 32D. Same cup volume, tighter band.
- Band digs in or too tight → Go up a band size and down a cup: 34C → 36B. Same cup volume, roomier band.
Sister sizing is also useful when shopping and your exact size is out of stock. A 34D and 32E hold the same amount of breast tissue, so fit should be nearly identical.
Signs Your Bra Doesn't Fit
Even if your calculated size is correct, bra fit can be off due to style, brand differences, and body shape. Watch for these signs:
Band rides up in back: The band is too loose. It should be nearly horizontal across your back. If it creeps up toward your shoulder blades, go down a band size.
Underwire sits on breast tissue: The underwire should rest flat against your ribcage, completely encircling the breast. If it sits on soft tissue, the cup is too small — go up a cup size.
Gaps at the top of the cup: If there's empty fabric at the top, the cup is too large or the wrong shape. Try a smaller cup first; if the gap is more crescent-shaped, a full-coverage style may fit better.
Straps digging in: Straps should provide only about 20% of breast support. If they dig into your shoulders, your band is doing too little work — the band is too large. Tighten the band first before adjusting straps.
Center gore doesn't lie flat: The small panel between the cups should lay flat against your sternum. If it sticks out, the cups are too small.
When to Remeasure
Your bra size changes more often than you might expect. Remeasure when:
- Weight changes by 10 pounds or more
- During and after pregnancy
- During and after breastfeeding
- After any breast surgery
- Every 6-12 months as a general rule
Brands also size differently. Victoria's Secret cups tend to run slightly small; ThirdLove offers half-cup sizes for precision; Wacoal cups typically run full. Your calculated measurement is a starting point — always try before you buy when a brand is new to you.
International Size Conversion
Bra sizing systems differ significantly between countries. A US 34D is not the same as a UK 34D past the D cup — the cup letter progression diverges:
- US: A, B, C, D, DD, DDD, G, H
- UK: A, B, C, D, DD, E, F, FF, G
- EU: A, B, C, D, E, F, G (with centimeter band numbers: 70, 75, 80, 85, 90)
- AU: Uses UK cup system but different band numbers (US 34 = AU 12)
Use the Bra Size Calculator to convert your measurements across all four systems at once.
Bra Size Calculator
Calculate your bra size from band and bust measurements