👙 ThirdLove Bra Size Calculator 2026
Find Your Perfect Fit with Half-Cup Sizes
The only bra size calculator with half-cup sizes for the perfect fit
Why Half-Cup Sizes Matter
ThirdLove pioneered half-cup sizes because most women fall between traditional cup sizes. Our calculator includes options like 34½, 36½, and more — giving you 80+ size options for the perfect fit.
Step 1: Find Your Band Size
Measuring Your Underbust
To find your band size, you will need your underbust measurement.
Wrap a soft measuring tape around your body, just under where the bra band lays. Make sure the tape is level with the floor and isn't hiking or falling in the back.
Use your measurement and the chart to determine your band size.
| Underbust | Band Size |
|---|---|
| 25-28.5" | 30 |
| 28.5-30.5" | 32 |
| 30.5-32.5" | 34 |
| 32.5-34.5" | 36 |
| 34.5-36.5" | 38 |
| 36.5-38.5" | 40 |
| 38.5-40.5" | 42 |
| 40.5-42.5" | 44 |
| 42.5-44.5" | 46 |
Step 2: Measure Your Bust
Measuring Your Bust
In order to find your size, you will also need to measure your bust.
Wrap the tape around the fullest part of your bust. Make sure the tape is level with the floor and fits snugly.
Note down this measurement as you'll use it to figure out your bra cup size.
Step 3: Determine Your Cup Size
Finally, to determine your bra cup size, you need to calculate the difference between your bust and underbust measurement. Subtract your underbust measurement from your bust measurement. Use the difference in inches and your band size to find the corresponding bra size.
👙 Your ThirdLove Bra Size
👯 Sister Sizes
If your size is unavailable, try these equivalent sizes:
Cup Size Formula
ThirdLove Cup Size Chart
Find where your band size row meets your cup difference column:
| Diff | <3" | 3-3.5" | 3.5-4" | 4-4.5" | 4.5-5" | 5-5.5" | 5.5-6" | 6-6.5" | 6.5-7" | 7-8" | 8-9" | 9-10" | 10-11" | 11-12" | 12-13" | 13-14" |
|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|
| 32 | 32AA | 32B½ | 32C | 32C½ | 32D | 32D½ | 32E | 32E½ | 32F | 32G | 32H | — | — | — | — | — |
| 34 | 34AA | 34A½ | 34B | 34B½ | 34C | 34C½ | 34D | 34D½ | 34E | 34F | 34G | 34H | — | — | — | — |
| 36 | 36A | 36A½ | 36B | 36B½ | 36C | 36C½ | 36D | 36D½ | 36E | 36F | 36G | 36H | — | — | — | — |
| 38 | 38A | 38A½ | 38B | 38B½ | 38C | 38C½ | 38D | 38D½ | 38E | 38F | 38G | 38H | — | — | — | — |
| 40 | — | 40A | 40B | 40B½ | 40C | 40C½ | 40D | 40D½ | 40E | 40F | 40G | 40H | — | — | — | — |
| 42 | — | — | 42B | 42B½ | 42C | 42C½ | 42D | 42D½ | 42E | 42F | — | — | — | — | — | — |
| 44 | — | — | 44B | 44C | 44C | 44C½ | 44D | 44D½ | 44E | 44F | — | — | — | — | — | — |
| 46 | — | — | 46B | 46C | 46C | 46D | 46D | 46D½ | 46E | — | — | — | — | — | — | — |
- Measure your underbust — Wrap tape just below the bust, level with the floor.
- Measure your bust — Wrap tape around the fullest part of your bust.
- Calculate the difference — Bust minus underbust in inches.
- Find your band size — Use the underbust chart above.
- Find your cup size — Use the difference and band to find your size.
What Are Half-Cup Sizes?
💗 ThirdLove's Innovation
Half-cup sizes (like B½, C½, D½) are ThirdLove's solution for women who fall between traditional cup sizes. If a C cup is too small but a D cup gaps at the top, a C½ is your perfect fit.
- A½ = Between A and B cup
- B½ = Between B and C cup
- C½ = Between C and D cup
- D½ = Between D and DD/E cup
- E½ = Between E and F cup
Sister Sizes Explained
Sister sizes have the same cup volume but different band sizes. If your band feels too tight, try your sister size with a larger band and smaller cup (and vice versa).
| Smaller Band | Your Size | Larger Band |
|---|---|---|
| 32D | 34C | 36B |
| 34DD | 36D | 38C |
| 36E | 38DD | 40D |
ThirdLove Official Resources
Frequently Asked Questions
ThirdLove offers half-cup sizes (like B½, C½, D½) that traditional brands don't carry. This means 80+ size options for a more precise fit. They found that most women fall between cup sizes, so half-cups solve this problem.
This calculator uses the official ThirdLove measurement method. However, body shape, breast tissue, and personal preference also matter. ThirdLove offers a "Try Before You Buy" program and free exchanges to ensure you find your perfect fit.
If your underbust measurement falls between sizes, round to the nearest even number. If you prefer a snugger fit, round down; for a looser fit, round up. Remember, bands stretch over time.
If your current bra cups gap at the top but the next size down is too small, you need a half-cup. Signs include: spillage in smaller cups, gaping in larger cups, or the underwire sitting on breast tissue.
Sister sizes have the same cup volume but different band sizes. For example, 34C, 36B, and 32D are sisters. If you need a tighter band, go down in band and up in cup. For a looser band, go up in band and down in cup.
The band should be snug and level around your body. You should be able to fit two fingers under it comfortably. 80% of support comes from the band, so it's the most important fit element.
Re-measure every 6-12 months, or after significant weight changes, pregnancy, or hormonal changes. Your bra size can fluctuate throughout your life.
US and UK band sizes are the same, but cups differ after D. US: D, DD, DDD, G, H. UK: D, DD, E, F, FF, G. ThirdLove uses US sizing but the calculator shows both.
This calculator is optimized for ThirdLove sizing. Other brands may vary slightly. For traditional brands (without half-cups), round to the nearest full cup size. The band size should be consistent across brands.
Yes! ThirdLove offers bands from 30 to 48 and cups from AA to I (including half-cups). They have an extensive size range designed to fit 80+ body types.
Created by OmniCalculator.space — Your trusted source for sizing calculators.
Last Updated: January 2026 | Not affiliated with ThirdLove