Bra Size Calculator (ABTF Style)
Use all six measurements for a better starting size estimate: 3 underbust + 3 bust measurements.
Underbust Measurements
Bust Measurements
Tip: This gives a starting size. Brand differences, cup shape, and style can change your best fit.
How this bra fitting calculator works
This tool follows the same general idea used by many “A Bra That Fits” communities: combine multiple body measurements to estimate a more accurate band size and cup size than older “add 4 inches” rules. The result is designed to be a practical starting point for bra shopping, not a final absolute size.
Instead of relying on one underbust and one bust number, this calculator uses six measurements to account for compression tolerance and breast shape variation:
- Loose, snug, and tight underbust for band estimation
- Standing, leaning, and lying bust for cup-volume estimation
How to measure correctly
1) Underbust measurements
Wrap a soft tape measure directly under your bust and keep it level all around.
- Loose: tape resting lightly on skin.
- Snug: comfortably firm, like how you want a supportive band to feel.
- Tight: as tight as you can comfortably pull the tape.
2) Bust measurements
Measure around the fullest part of your bust while keeping the tape level:
- Standing: upright posture, normal breathing.
- Leaning: bend forward around 90° at the waist.
- Lying: lie on your back and measure around fullest point.
These three bust positions help estimate volume more reliably, especially if you have softer tissue, projection, or asymmetry.
Understanding your calculator result
You’ll receive a suggested UK size and US size as a starting point. Since bra labeling is inconsistent across brands, always try nearby sizes too. Focus on fit signs:
- Band stays level and feels supportive on the loosest hook when new.
- Center gore sits close to sternum (in most wired bras).
- Cups contain tissue without overflow, wrinkling, or major gaping.
- Straps support gently without digging (band should do most support work).
Sister sizes: your best backup options
If your calculated size is close but not perfect, sister sizes can help:
- Go down a band, up a cup for a tighter band with similar cup volume.
- Go up a band, down a cup for a looser band with similar cup volume.
Example: if 34F is close, you might also test 32FF and 36E (UK progression).
Common fit issues and quick fixes
Band rides up
Try a smaller band size, or confirm your band isn’t stretched out from wear.
Spillage at top or sides
Increase cup volume, and check cup shape compatibility (not just size).
Gaping at top of cup
Try a smaller cup, a shorter cup shape, or a style better suited to your upper fullness pattern.
Wire sits on breast tissue
Usually indicates cup size too small or cup shape too shallow.
Final note
A bra size calculator is a strong first step, but real fit comes from trying styles that match your shape, support preference, and comfort needs. Use this result as your baseline, then test nearby sizes and styles until the fit feels secure, balanced, and comfortable all day.