Band Size Calculator
The band does most of the supporting work in a bra — it anchors the bra to your ribcage and carries the weight, while the straps mainly steady the cups. That is why getting the band right matters more than most people expect: a band that is too loose rides up your back and leaves the straps doing work they were not designed for, while a band that is too tight digs in and makes the whole bra uncomfortable. This band size calculator works from a single measurement — your underbust — and gives you the band size in all seven sizing systems we support (US, UK, EU, FR, AUS, JP and IN), plus the sister bands that hold a similar cup volume if your usual band is out of stock.
Use the Simple mode below: enter your underbust measurement and your bust measurement, pick the country system you shop in, and the calculator will show your full estimated size with the band highlighted. The band number is what this page is about — the cup letter comes along for the ride, and the bra size chart shows how the two combine. If you want a more refined estimate from six measurements, use the advanced bra size calculator; if you are unsure how to measure, read how to measure your bra size first.
Enter Your Measurements
Advanced mode uses three underbust and three bust measurements for a more refined estimate. Measuring guide.
How the Calculation Works
Band sizing looks different in every country, but every system starts from the same measurement: your underbust. Here is how the calculator turns that one number into a band in each system.
- Measure snugly and level. Wrap a soft tape directly under your bust, where a bra band would sit, and pull it close against your body with no slack — you should just be able to slip a finger underneath. Check in the mirror that the tape is level around your back, and read the number on a normal exhale. Do not add inches: modern bands are designed to stretch and fit your real measurement, and the old habit of adding 4 or 5 inches is one of the most common reasons bands end up too loose.
- US, UK and IN bands. Your underbust in inches is rounded to the nearest even number — 32, 34, 36, and so on. Bands are only sold in even numbers, so this rounds your real measurement to the closest size you can actually buy. An underbust of 33 inches rounds to a 34 band; 35.5 inches rounds to a 36 band.
- EU and JP bands. Your underbust in centimeters is rounded to the nearest 5 — 75, 80, 85, and so on. A 78 cm underbust rounds to an 80 band; an 82 cm underbust also rounds to 80.
- FR bands. French sizing takes the EU band and adds 15, so an 80 EU band is a 95 FR band. If you shop French brands, use the FR option in the country dropdown rather than converting in your head.
- AUS bands. Australian sizing takes the inch band and subtracts 22, so a 34 inch band is a 12 AUS band. New Zealand follows the same AUS numbering.
- Unit conversion. If you enter centimeters, the calculator converts to inches by dividing by 2.54 before running the sizing math, and converts back for the EU, FR and JP band numbers.
- An estimate, not a verdict. Bands vary between brands and styles — some run firm, some run stretchy — so use the result as a starting point and judge the fit by how the band feels: level around your body, snug on the loosest hook when new, and staying put when you raise your arms.
Sister Bands: the Same Cup Volume on a Different Band
If your band size is out of stock, a sister size keeps roughly the same cup volume on a different band: go one band up and one cup down, or one band down and one cup up. A 34C, for example, has sister sizes 32D and 36B — the cup holds about the same volume, but the band fits a smaller or larger ribcage. Sister sizes are a useful fallback, not a perfect substitute: the band is the part doing the supporting, so a sister band that is too loose will still ride up even if the cups feel right. Use the sister size calculator to find yours for any size.
Band Conversion Table
Use this table to convert a band between systems at a glance. Cup letters are not shown here because they follow their own rules in each system — see the bra size chart for the full picture.
| Underbust (in) | US / UK / IN | EU / JP | FR | AUS / NZ |
|---|---|---|---|---|
| 28–29 | 28 | 60 | 75 | 6 |
| 30–31 | 30 | 65 | 80 | 8 |
| 32–33 | 32 | 70 | 85 | 10 |
| 34–35 | 34 | 75 | 90 | 12 |
| 36–37 | 36 | 80 | 95 | 14 |
| 38–39 | 38 | 85 | 100 | 16 |
| 40–41 | 40 | 90 | 105 | 18 |
| 42–43 | 42 | 95 | 110 | 20 |
| 44–45 | 44 | 100 | 115 | 22 |
Band numbers are rounded to the nearest even inch (US/UK/IN) or nearest 5 cm (EU/JP) from your underbust measurement. If your underbust falls exactly between two bands, try both and keep the one that stays level and comfortable on the loosest hook.
Keep Exploring
Your band size is only the beginning. These resources help you check the cup, convert between systems, and solve fit problems when the band still does not feel right:
- How to measure your bra size — a step-by-step guide to measuring your underbust and bust at home.
- Bra size chart — US, UK, and EU band and cup sizes in one conversion table.
- Sister size calculator — find alternative sizes with a similar cup volume but a different band.
- Bra size calculator — the full calculator, with simple and advanced modes.
- Global size converter — convert a size you already know between sizing systems.
- How to find the right bra size and understand sister sizes — a longer guide on the blog.
Frequently Asked Questions
How do I measure my underbust for the band size?
Wrap a soft tape directly under your bust, where a bra band would sit, and pull it snug — close against your body with no slack, but not digging in. Keep the tape level around your back (check in the mirror), breathe normally, and read the number on an exhale. That single number sets your band.
Why are band sizes always even numbers?
Bra bands are manufactured in even-numbered sizes — 28, 30, 32, 34, and so on — in US, UK and IN sizing. The calculator rounds your underbust to the nearest even inch so the result matches a size you can actually buy. EU and JP bands use multiples of 5 cm instead, and FR adds 15 to the EU band.
What if my underbust falls between two band sizes?
Try both. If the smaller band feels snug but comfortable on the loosest hook, it will usually be the better choice, because bands stretch a little with wear and you can move to tighter hooks later. If it digs in or leaves marks, go up a band and check the cup still fits — or try a sister size.
Do band sizes differ between brands and countries?
Yes, on both counts. Bands vary between brands — some run firm and some run stretchy — and the numbering differs between systems: a US 34 is an EU 75, a FR 90 and an AUS 12. Always check the system on the label, and use the country dropdown in the calculator to match the brands you shop.