ABraThatFits Size Calculator
Use all six measurements for a better starting size estimate. This tool returns a suggested UK bra size plus sister sizes.
What is an ABraThatFits calculator?
The ABraThatFits calculator is a measurement-first approach to finding a bra size that actually supports your body. Unlike old “add four inches” sizing rules, this method uses six measurements to estimate both your band size and cup volume. The result is a practical starting point for fit testing, not a rigid final answer.
Why six measurements matter
Most quick bra calculators use only two numbers. That can miss important details like tissue distribution and how compressible your ribcage is. The six-input model gives better context:
- Loose/Snug/Tight underbust helps estimate a comfortable and supportive band.
- Standing/Leaning/Lying bust helps estimate cup volume across different positions.
- The average bust value smooths out one-off measuring errors.
How to measure correctly
1) Underbust
Measure directly under your bust with no padding and a soft tape measure.
- Loose: tape just touching the skin.
- Snug: comfortably firm, like a band you would wear all day.
- Tight: as tight as possible without pain.
2) Bust
Measure at the fullest part of your bust.
- Standing: upright, relaxed posture.
- Leaning: bend forward around 90 degrees so tissue falls away from the chest wall.
- Lying: lie flat on your back and measure again.
How to use your calculator result
Your output includes a suggested UK size and sister sizes. Start with the suggested size, then test nearby options based on feel and fit.
Fit checklist
- Band sits level and feels secure on the loosest hook.
- Underwire follows breast root and does not sit on tissue.
- Center gore (middle panel) sits close to the sternum (for wired bras).
- Cups contain tissue without gaping or spilling.
- Straps support but do not carry all the weight.
Common fitting adjustments
- Band feels too tight but cups seem okay: try one band up and one cup down (sister size).
- Band rides up: go down in band and up in cup to keep volume similar.
- Spillage at top/side: increase cup size, then reassess band.
- Cup wrinkling: smaller cup or different shape may work better.
Important notes
Bra sizing is not universal across brands. A 32F in one brand may fit like a 30FF or 34E in another. Use this tool as your baseline, then refine by trying multiple styles and constructions (balconette, plunge, full cup, and wireless options).
If your size changes throughout your cycle, consider keeping two nearby sizes in rotation for comfort and consistency.