A bra calculator can be used to help determine bra size. The big caveat is that most bra calculators are absolute garbage; they're so bad as to be completely useless.
Bra fit calculators
There are a few fit calculators that yield accurate results.[1]
- SizemApp Bra Size Calculator using 6 sets of different measurements, most accurate
- "Bra Calculator", the most commonly used calculator from A Sophisticated Pair (use "very snug" setting)
- "Bra Size Calculator", a calculator from Butterfly Collection Lingerie