Bra Size Calculator · Practical guide
How to Measure Bra Size at Home
Two tape-measure readings are all you need to estimate your band and cup size.
At a glance
The Two Measurements You Need
Measuring your bra size at home takes two readings with a soft tape measure: your under-bust (snug, directly beneath the breasts) for the band, and your fullest bust (tape level across the fullest point, usually the nipple line) for the cup. Subtract band from bust to get the cup difference. For example, an under-bust of 34 inches and a bust of 38 inches gives a 4-inch difference — a 34D.
Interactive tool
Bra Size Calculator
Enter your own values, then compare the result with the examples below.
Results
Step-by-Step Measuring Tips
- Wear an unlined, non-padded bra — or no bra — so the tape reads your true shape.
- Keep the tape parallel to the floor all the way around your back.
- Exhale normally before reading the under-bust measurement; it should be snug but not tight.
- Measure to the nearest half inch and write both numbers down.
- Re-measure every 6–12 months, since weight changes, pregnancy, and age all shift sizing.
Worked Example
Say your under-bust reads 31.5 inches. Rounded to the nearest whole number that is 32, which is already even, so the band stays 32. If your fullest bust is 36 inches, the difference is 36 − 32 = 4 inches, which maps to a D cup. Your estimated size is 32D in both US and UK sizing. If the under-bust had been 33 inches instead, the band would round up to the next even number, 34, and the same 36-inch bust would give a 2-inch difference — a 34B. Small changes in measurement can move both the number and the letter.
Why Home Measuring Is Only a Starting Point
A tape measure captures circumference, not shape, so breast fullness, spacing, and tissue firmness can all make the same size fit differently. Use your calculated size as a starting point, then adjust by trying one band or cup up and down. A professional fitting is the gold standard if a calculated size consistently feels wrong.
Frequently Asked Questions
Should I measure with or without a bra on?
Measure in an unlined, non-padded bra or no bra at all. Padding and push-up styles add volume that inflates the bust reading and skews the cup size.
How often should I re-measure my bra size?
Every 6 to 12 months is a good rule, and always after significant weight change, pregnancy, or breastfeeding. Bodies change more often than bras get replaced.
My under-bust is an odd number. What band size do I buy?
Round up to the next even number — a 33-inch under-bust becomes a 34 band. Most brands only make even band sizes.
Why does my measured size feel too tight or too loose?
Shape, breast spacing, and brand differences all affect fit. Try the sister sizes one band up and cup down, or one band down and cup up, to fine-tune the fit.