To compare bra sizing between brands, first convert both labels into the same sizing system. Then compare the exact models by band firmness, cup volume, depth, wire width, cup height and material. A brand chart alone cannot tell you whether two bras will fit the same way.
Start with one bra that fits well
Your best reference is not a theoretical average. It is a specific bra that fits your body.
Record:
- brand;
- model;
- sewn-in size;
- sizing system;
- approximate age;
- hook used;
- band feel;
- cup volume;
- cup depth;
- wire width;
- cup height;
- strap placement.
This becomes the benchmark for the new brand.
Step 1 - normalise the sizing system
Check whether each label is:
- UK;
- US/Canada;
- EU;
- French;
- Australian/New Zealand;
- another system.
Do not compare letters until this is clear.
Step 2 - compare the band
Ask:
- Is the official chart based on body measurement or garment measurement?
- Is the band described as firm, true or stretchy?
- How tall is the band?
- How many hooks does it use?
- Is the fabric rigid, mesh or highly elastic?
- Do repeated model-specific reviews mention the same band behaviour?
If your reference band is ideal and the new model is consistently firmer, the closest larger-band sister size may be worth testing. Do not assume the whole brand has one band rule.
Step 3 - compare cup volume
Start with the converted equivalent.
Then look for evidence that the model:
- runs small or large in volume;
- has a stretch upper cup;
- uses rigid foam;
- is closed or open at the neckline;
- has unusually tall cups.
When possible, order the converted starting size and one adjacent cup in the same band.
Step 4 - compare cup shape
This is often more important than a one-cup difference.
Compare:
- shallow vs projected;
- narrow vs wide wires;
- short vs tall cups;
- low vs high gore;
- close vs wide strap placement;
- flexible vs rigid material.
A review stating “cup runs large” may actually describe a tall or open cup on a fuller-on-bottom shape.
Step 5 - compare the exact model, not only the logo
Within one brand:
- a plunge can have narrow wires;
- a T-shirt bra can be shallow;
- a full-cup style can be tall;
- a stretch-lace model can adapt across a range.
Create brand guides at model level whenever possible. General brand statements should be labelled as broad tendencies, not rules.
A practical comparison worksheet
| Feature | Known bra | New bra | What it suggests |
|---|---|---|---|
| System | UK | US | Convert first |
| Band | Firm 34 | Stretchy 34 | 34 may still work |
| Cup | Seamed, projected | Moulded, shallow | Shape risk |
| Wire | Narrow | Wide | May create side space |
| Upper cup | Stretch lace | Rigid edge | Possible cutting or gap |
| Returns | Easy | Paid international | Order fewer, deliberate sizes |
How to use official charts
Official charts are the first reference for the brand’s labelling, but they have limits.
Check:
- publication date;
- country version;
- whether the chart applies to the specific line;
- whether band labels are converted;
- whether the cup sequence matches the products.
Do not copy a brand chart into Bra Size Calculator Pro without attribution, review date and permission where required.
How to use wearer feedback responsibly
A useful aggregated note needs:
- enough observations;
- exact model;
- known comparison sizes;
- consistent terminology;
- a date range;
- disclosure that it is wearer-reported.
Do not publish “Brand X runs one cup small” from a handful of anonymous comments.
Choose the test size set
Recommended order:
- converted baseline;
- one adjacent cup in the same band;
- closest sister size if band behaviour is uncertain;
- different style if the geometry is clearly different.
Avoid moving several sizes before learning what failed.
The practical takeaway
A useful brand comparison is a structured comparison of garments, not a table that claims every 34D is interchangeable.
Normalise the system, anchor to a known bra, compare the exact construction and test one deliberate alternative at a time. The result is a better starting point and a reusable understanding of what your body needs from a bra.