Bra Size Calculator

80% of women wear the wrong bra size. Do you? Use our bra measurement calculator to find out.

Underbust Measurement

Bust Measurement

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How ThirdLove Bra Sizing Works

How our Bra Size Calculator finds your size, so you can measure yourself and read ThirdLove sizes.

How to Measure Your Band and Cup Size

All you need is a soft measuring tape. Measure in inches.

Find your band size. Wrap the tape around your body, just under where the bra band lays (your underbust). Make sure the tape is level with the floor and isn't hiking or falling in the back. Find your underbust measurement in the band size chart (step 1).
Find your cup size. Wrap the tape around the fullest part of your bust. Make sure the tape is level with the floor and fits snugly. Subtract your underbust measurement from your bust measurement, then find the difference in your band's column of the bra size chart (step 2).

For example, an underbust of 31 in is a 34 band. With a bust of 36.25 in, the difference is 5.25 in, which is a 34C.

Our Bra Size Calculator does the same math for you: enter both measurements in inches.

Step 1: Band size by underbust measurement (inches). Each range excludes its lower value and includes its upper value.
Underbust (in)	Band size
24.9 – 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

Step 2: Bra size by band and by bust minus underbust (inches). Each range excludes its lower value and includes its upper value.
Bust − underbust (in)	Band 30	Band 32	Band 34	Band 36	Band 38	Band 40	Band 42	Band 44
Up to 2.5			34AA
2.5 – 3	30B^*	32A^*	34AA^*
3 – 3.5	30C	32B	34A
3.5 – 4	30C½	32B½	34A½
4 – 4.5	30D	32C	34B	36A^*
4.5 – 5	30D	32C½	34B½	36A½
5 – 5.5	30E	32D	34C	36B	38A^*
5.5 – 6	30E½	32D½	34C½	36B½	38A½
6 – 6.5	30F	32E	34D	36C	38B
6.5 – 7	30F	32E½	34D½	36C½	38B½
7 – 8	30G	32F	34E	36D	38C	40B^*
8 – 9		32G	34F	36E	38D	40C	42B^*
9 – 10			34G	36F	38E	40D	42C	44B^*
10 – 11			34H	36G	38F	40E	42D	44C
11 – 12				36H	38G	40F	42E	44D
12 – 13					38H	40G	42F	44E

* Also the result when the difference is exactly 2.5 in: 30B, 32A, 34AA; 4 in: 36A; 5 in: 38A; 7 in: 40B; 8 in: 42B; 9 in: 44B.

The calculator only gives a size for an underbust over 24.9 in, up to 42.5 in, with a difference of up to 13 in. Blank cells and measurements outside these ranges have no size in the calculator.

Sister Sizes

Sister sizes have the same cup volume on a different band. One band size up and one cup letter down gives a sister size, and so does one band size down and one cup letter up: 32D, 34C and 36B are sister sizes. Half cups keep their half, so 32D½, 34C½ and 36B½ are sister sizes too.

If your band rides up in the back but the cups fit well, try going down a band size and up a cup size for an equivalent volume (your sister size).

Sister sizes among the sizes our Bra Size Calculator gives (each line has the same cup volume):

30B, 32A, 34AA
30C, 32B, 34A
30C½, 32B½, 34A½
30D, 32C, 34B, 36A
32C½, 34B½, 36A½
30E, 32D, 34C, 36B, 38A
30E½, 32D½, 34C½, 36B½, 38A½
30F, 32E, 34D, 36C, 38B
32E½, 34D½, 36C½, 38B½
30G, 32F, 34E, 36D, 38C, 40B
32G, 34F, 36E, 38D, 40C, 42B
34G, 36F, 38E, 40D, 42C, 44B
34H, 36G, 38F, 40E, 42D, 44C
36H, 38G, 40F, 42E, 44D
38H, 40G, 42F, 44E

ThirdLove Half Cup Sizes

ThirdLove created half cup sizes to help every bra wearer find the right size for their body. In between cup sizes? Go up or down a half cup.

A half cup sits halfway between two whole cups on the same band. On a 34 band, a difference between bust and underbust of 5–5.5 in gives a 34C, 5.5–6 in a 34C½ and 6–6.5 in a 34D.

Half cup sizes our Bra Size Calculator gives, by band
Band	Half cup sizes
30	30C½, 30E½
32	32B½, 32C½, 32D½, 32E½
34	34A½, 34B½, 34C½, 34D½
36	36A½, 36B½, 36C½
38	38A½, 38B½

Cup Letter Equivalents

After D, ThirdLove cup sizes use single letters: E, F, G and H. Our size selectors show each one next to its multiple-D letters.

ThirdLove cup letters and their multiple-D equivalents
ThirdLove cup	Same as
E	DD
E½	DD½
F	DDD
G	DDDD
H	DDDDD

Thirdlove offers over 60 bra sizes from 32 to 44 band and bra cup sizes from AA to H cup, including our exclusive half cup sizes.

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Use our bra cup size calculator above to instantly calculate your size. Want to learn how to calculate your bra size yourself? Follow our easy steps below to learn!

Finding Your Band Size

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To find your band size, you will need your underbust measurements.

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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.

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Use your measurement and the chart to determine your band size.