A Bra That Fits Calculator – Find Your Size
Use this A Bra That Fits Calculator to estimate your UK bra size from simple underbust and bust measurements, then fine-tune the result with sister sizes and fit checks.
Choose Quick Mode for a fast estimate, or Accurate Mode for a more careful result using loose, snug, tight, standing, leaning, and lying measurements.
1 Underbust (Band)
2 Bust (Cup)
Your result is a starting size, not a final rule. Bra fit can change by brand, style, fabric, and personal comfort.
Sister Sizes
If the band feels too firm or too loose, these nearby sizes may help:
International Conversions
Quick Fit Checklist
- The band should sit level around your body and feel firm without digging in.
- The centre gore should rest flat and feel comfortable.
- The cups should contain breast tissue smoothly, without overflow or gaps.
Why Use This A Bra That Fits Calculator?
Many size charts still use the old “+4” method, which can make the band feel too loose and the cup feel smaller than expected. A closer underbust measurement usually gives a more useful starting point.
This calculator uses UK-first fitting logic to suggest a practical starting size. Use Quick Mode when you want a fast estimate, or Accurate Mode when you want the result to consider all six measurements.
How to Measure for a Bra
1. The Underbust (Band)
Measure around your ribcage directly under your bust. Keep the tape level and parallel to the floor.
- Snug: Comfortably firm, this is the main band measurement.
- Tight: Firm after a full exhale, used to judge band support.
- Loose: Tape resting on the skin with a neutral breath.
2. The Bust (Cup)
Measure around the fullest part of the bust. Keep the tape lightly touching, without pressing into the body.
- Standing: Measure while standing in a normal posture.
- Leaning: Lean forward about 90°, useful when the standing measure does not tell the full story.
- Lying: Measure while lying flat on your back.
Frequently Asked Questions
How accurate is this bra size calculator?
This calculator gives a useful starting size using modern UK fitting logic, not the outdated “+4” method. For the best result, use Accurate Mode and take each measurement carefully. Brand and style differences still matter, so use the size as a starting point and adjust by fit.
Should I add 4 inches to my band size?
Generally, no. Modern bras are usually designed to fit closer to the underbust. Adding 4 inches can make the band too loose, which may cause it to ride up and reduce support.
What are sister sizes and when should I use them?
Sister sizes have the same cup volume with a different band. If the band feels too tight, go up a band and down a cup (e.g., 34E to 36DD). If the band feels too loose, go down a band and up a cup (34E to 32F).
Why does my band ride up at the back?
A band that rides up is usually too big or too stretchy. The band should sit level around your body and do most of the support work. Try a smaller band and increase the cup letter to keep the same cup volume.
What does it mean if the centre gore does not sit flat?
The gore is the centre panel between the cups. If it does not sit flat, the cups may be too small, the wire shape may not suit you, or the style may not have enough depth. Trying a larger cup or a different shape can help.
What is the difference between UK and US cup sizes?
UK and US sizes match up to D, then they diverge. UK uses double letters like DD, FF, and GG, while US typically progresses differently (DD, DDD/F, G, H, etc.). This tool shows conversions to make shopping easier.
Why did this calculator give me a different size than I usually wear?
A different result is common, especially if your current size came from the old “+4” method or a store chart. This A Bra That Fits Calculator uses your actual measurements, so the suggested band may be smaller and the cup letter may look larger while the cup volume still makes sense.
Should I measure with a bra on or off?
For the cleanest measurement, measure without a bra. If that is uncomfortable, use a non-padded bra that does not compress or add volume. Keep the tape level, and avoid pulling it too tight for bust measurements.
What if one breast is larger than the other?
That is very common. Fit the cup to the larger side first. You can adjust the strap slightly on the smaller side or use a removable pad if it feels more comfortable.
Disclaimer: Bra sizing is a starting point. Comfort and fit can vary by brand, style, fabric, and body shape.