How to find your bra size at home
Two measurements, one subtraction and a sister size. No +4 myth, no guesswork.
Most women are wearing the wrong bra size. Not because they cannot measure, but because the instructions are wrong. The old “add four inches to your underbust” rule was invented for a different era of elastic. Use the actual number.
Step 1: underbust
Wrap a soft tape around your ribcage, directly under the bust, and breathe out. Keep it snug — if it slides down, it is too loose.
Step 2: full bust
Wrap the tape around the fullest part of the bust, parallel to the floor. Do not pull it tight or push the breasts down.
Step 3: the cup difference
Full bust minus underbust gives the cup. The size guide has the full table.
Step 4: try the sister size
If 36C is close but the band rides up, try 34D. If 34D digs in at the band but the cup is right, try 36C.
The three signs a bra is not doing its job
- The band rides up when you lift your arms — it is too loose.
- The centre panel does not sit flat — the cup is too small or the shape is wrong.
- The straps leave deep marks or fall down — they are doing the band’s work.
Still unsure? Take the 60-second quiz or message a fit specialist.