Bra Size vs Shoe Size
The bra size estimate and the shoe size formula are the personal measurements set’s two body-measurement-to-size mappings that work from a small number of entered values. Both are named OverCalculator legacy methods: the bra estimate is oc-bra-legacy-v1, a two-measurement arithmetic estimate, and the shoe formula is oc-shoe-legacy-formula-v1, a branch-selected set of US, UK, and EU equations. Neither is a universal standard — the bra method is not a universal US, UK, retailer, or manufacturer system, and the shoe formula is not assessed against ISO 9407, the Mondopoint sizing standard. The genuine choice is which mapping matches the measurement you have: two torso circumferences, or a size or foot length for one branch.
What each calculator does
The bra size estimate takes a snug underbust and the circumference at the fullest part of the bust, in inches or centimeters. It rounds the underbust to the nearest even band, subtracts it from the bust, rounds the difference to a whole-number position, and maps that position to a stored cup label from AA through K. With 34 in underbust and 37 in bust, the band stays 34, the difference is 3.0 in, and position 3 maps to C, so the estimate is 34C. A difference below the first label is held at the first and one beyond the stored list at the last — legacy rules, not universal sizing.
The shoe size formula starts from a selected group — men’s, women’s, or children’s — and an input system: US, UK, EU, or CM. It converts the input to an assumed foot length, then applies the retained equations for that branch. For men’s US 10, the assumed foot length is ((10 + 23) ÷ 3) × 2.54 = 27.94 cm, and the crosswalk is US 10.0, UK 9.5, EU 44, with 27.9 cm assumed foot length; women’s US 10 returns US 10.0 and UK 8.0. The CM input means assumed foot length inside this formula, which can differ from a manufacturer’s CM label, and the page’s fit-check workflow directs you to the exact manufacturer or model chart.
Side-by-side comparison
| Feature | Bra size estimate | Shoe size formula |
|---|---|---|
| Named method | oc-bra-legacy-v1 | oc-shoe-legacy-formula-v1 |
| Inputs | Underbust and fullest-bust circumference | Group plus US, UK, EU, or CM value |
| Core relationship | Even band plus whole-number cup position from the difference | Input → assumed foot length → branch-specific US/UK/EU equations |
| Worked example | 34 in + 37 in → 34C | Men’s US 10 → US 10.0, UK 9.5, EU 44, 27.9 cm |
| Standard status | Not a universal sizing system | Not assessed for ISO 9407 (Mondopoint) conformance |
| What you must do | Verify fit with the brand’s chart | Confirm against the exact manufacturer chart, including CM-label meaning |
When to use which
Use the bra size estimate when your measurement is for apparel: you have underbust and fullest-bust values and want a first size to try. Treat the estimate as the first item to try, check the brand’s own chart before ordering, and assess band, cup, straps, and center fit together. Use the shoe size formula when you have a starting US, UK, EU, or foot-length value and want the legacy crosswalk for that branch, then measure both feet per the manufacturer’s guidance, use the larger relevant measurement, and confirm against the exact chart — length conversion alone does not establish fit. Both results are navigation aids, not fit guarantees, and neither is a standard-conforming size.
Where to start
- Bra size estimate — legacy two-measurement method with a first size to try and brand verification steps.
- Shoe size formula — branch-selected US, UK, and EU crosswalk from a size or assumed foot length.
Informational note: This page is an educational comparison of two legacy sizing tools. Neither method is a universal sizing system, and the shoe formula has not been assessed for ISO 9407 (Mondopoint) conformance. Confirm every result against the exact chart of the brand or manufacturer you are buying from, and treat both outputs as starting points for physical fitting.