How to Choose the Right Wireless Bra Size?

December 25, 2025

Comment Choisir la Taille de son Soutien-Gorge Sans Armature ?

You've decided to switch to a wireless bra, but a crucial question arises: what size should you choose? This question is all the more legitimate because wireless bras, with their flexibility and elasticity, can fit differently from the underwired models you're familiar with.

Choosing the wrong size is the #1 mistake that leads to the failure of a wireless bra. A poorly fitting model won't provide proper support, will cause discomfort, and will leave you thinking that "wireless bras aren't for you." When it's simply a matter of size.

In this comprehensive guide, we'll explain step-by-step how to take your measurements correctly, accurately calculate your size, understand the specifics of wireless bras, and avoid common mistakes. By the end, you'll know exactly what size to order with confidence.

Why Size is Even More Important in Wireless Bras?

Underwires Hide Sizing Errors

With an underwired bra, the rigid structure "forces" the shape and can partially compensate for an unsuitable size:

A band that is too large is held in place by the underwire
Cups that are too small are contained by the rigidity
A poor fit is masked by the structure

Result: 80% of women wear the wrong size with underwires... without even knowing it.

Wireless Bras Don't Cheat

In the absence of rigid underwiring, everything relies on precise adjustment:

The underbust band provides 80% of the support
The cups must perfectly hug the shape
The straps complement the support
No structure compensates for an error

Correct size = optimal comfort and support
Incorrect size = guaranteed failure

Flexibility Requires More Precision

The elastic fabric of wireless bras adapts better to morphological variations, but it must start from a correct base. A model that is too large will provide no support, a model that is too small will painfully compress.

Step 1: Taking Your Measurements Correctly

Required Material

Flexible tape measure (tailor's type)
Mirror (ideally large, to see your back)
Help from another person (optional but recommended for more accuracy)
Clothing: Topless or with a non-compressive bralette (never with a push-up or padded bra)
Our calculator free and fast

Ideal Conditions

Time: In the morning, before volume variations related to the day (water retention, diet)

Menstrual cycle: Avoid the days preceding your period when your breasts may be swollen

Temperature: Normal room temperature (neither too cold, nor right after a hot bath)

Measurement 1: The Underbust Measurement

What is the Underbust Measurement?

It's the circumference of your rib cage just below the breasts, where the bra band rests. This is the MOST IMPORTANT measurement because it determines 80% of the support.

How to Measure?

1. Tape measure positioning:

Place the tape measure horizontally under your bust
The tape must be perfectly straight and parallel to the floor at your back
Pass it just below the inframammary fold

2. Correct tension:

The tape should be firm but not tight
You should be able to slide one finger underneath
Do not compress, but do not let it float
The tape should not roll or slip

3. Body position:

Stand up straight
Arms at your sides
Breathe normally (do not inflate your rib cage)
Look straight ahead (not down)

4. Reading the measurement:

Exhale normally
Read the number where the tape meets
Note in centimeters
Round to the nearest centimeter

Example: If you read 87.5 cm, write 88 cm.

Tip for More Accuracy

Measure 3 times and average:

1st measurement: 87 cm
2nd measurement: 88 cm
3rd measurement: 88 cm
Average: (87+88+88)/3 = 87.7 → 88 cm

Measurement 2: The Bust Measurement

What is the Bust Measurement?

It's the circumference of your bust at the fullest part of your breasts (generally at nipple level). This measurement helps calculate the cup volume.

How to Measure?

1. Tape measure positioning:

Place the tape measure at the level of the fullest part of your breasts
The tape should be horizontal all around the bust
Warning: at the back, the tape tends to go down → check with a mirror

2. Without compression:

The tape should skim the skin without tightening
Do not compress the bust at all
Leave the bust in its natural shape

3. Body position:

Stand up straight
Arms at your sides (or slightly spread apart for measurement)
Lean slightly forward if you have a large bust (so the breasts fall naturally)
Breathe normally

4. Reading the measurement:

Read at the point where the tape meets
Note in centimeters
Round to the nearest centimeter

Example: If you read 102.5 cm, write 103 cm.

Common Mistake to Avoid

❌ Measuring with a push-up or padded bra → Distorts the measurement by adding artificial volume

✅ Measuring topless or with a thin bralette → Measures your actual breast size

Step 2: Calculating Your Size

Calculating the Underbust (Numbered Size)

Your underbust measurement corresponds to a standard size:

Measured Underbust	Bra Size
63-67 cm	80
68-72 cm	85
73-77 cm	90
78-82 cm	95
83-87 cm	100
88-92 cm	105
93-97 cm	110
98-102 cm	115
103-107 cm	120

Example: You measure 88 cm → Your size is 105

Calculating the Cup

The cup is calculated by the difference between your bust measurement and your underbust measurement.

Formula: Bust Measurement - Underbust Measurement = Difference in cm

Conversion chart:

Difference	Cup
12-13 cm	A
14-15 cm	B
16-17 cm	C
18-19 cm	D
20-21 cm	E
22-23 cm	F
24-25 cm	G
26-27 cm	H
28-29 cm	I
30-31 cm	J

Complete Example

Your measurements:

Underbust: 88 cm → Size 105
Bust: 111 cm

Calculation:

Difference: 111 - 88 = 23 cm
23 cm = Cup F

Your full size: 105F

Step 3: Specifics of Wireless Bras

Sizing Differences

Wireless bras can fit differently depending on the brand:

1. Standard Sizes (85B, 90C, 95D...) The majority of brands, including Twinswomen, use the standard French/European system.

2. Simplified Sizes (S, M, L, XL) Some bralette-type models offer grouped sizes:

Size	Equivalence
XS	80A - 85A
S	85B - 90B - 85C
M	90C - 95C - 90D - 95B
L	95D - 100D - 100C - 95E
XL	100E - 105E - 100F - 105D
XXL	105F - 110F - 105G

Important: These equivalences vary between brands. Always consult the specific guide.

3. UK/US Sizes If you are buying Anglo-Saxon brands:

UK → FR Cups:

DD (UK) = E (FR)
E (UK) = F (FR)
F (UK) = G (FR)
FF (UK) = G (FR)
G (UK) = H (FR)

The Concept of Sister Sizes

What is a Sister Size?

Sister sizes are different sizes that offer an equivalent cup volume. This is a little-known but extremely useful technique for adjusting comfort.

How Does It Work?

Principle: When you go up one band size, you go down one cup size to maintain the same volume.

Example: Sister sizes of 90C

85D (smaller band size, larger cup size)
90C (your size)
95B (larger band size, smaller cup size)

These three sizes have the same cup volume but different band sizes.

Complete Sister Size Chart

Size	Sister Size -	Sister Size +
85B	80C	90A
85C	80D	90B
85D	80E	90C
90B	85C	95A
90C	85D	95B
90D	85E	95C
90E	85F	95D
95C	90D	100B
95D	90E	100C
95E	90F	100D
95F	90G	100E
100D	95E	105C
100E	95F	105D
100F	95G	105E
105E	100F	110D
105F	100G	110E

When to Use Sister Sizes?

Situation 1: The band is too loose → Go down one band size, go up one cup size

Example: Your 95D is too loose → Try 90E

Situation 2: The band is too tight → Go up one band size, go down one cup size

Example: Your 95D is too tight → Try 100C

Situation 3: Your size is not available → Use a close sister size

Example: The model does not offer 90F → Order 95E or 85G

Checking if the Size is Correct

Underbust Band Test

Two-Finger Test:

Slide two fingers under the band at your back
You should be able to slide them comfortably
If you can fit your whole hand → Too big
If you cannot fit two fingers → Too tight

Horizontality Test:

Look at your back in a mirror
The band should be perfectly horizontal
If it rides up at the back → Too big
If it rolls up on itself → Too tight

Movement Test:

Raise your arms above your head
The band should not ride up more than 2-3 cm
If it rides up to the middle of your back → Too big

Positioning Test:

The band should be lower at the back than at the front
If it is higher at the back → Too big

Cup Test

Filling Test:

The cup should fully enclose the breast
No empty space in the cup → Cup too big
No spillage at the sides or top → Cup too small
The fabric should be smooth, without wrinkles

Center Test:

The center gore (between the two breasts) should lie flat against the sternum
If it floats → Cups too small or band too big
If it presses painfully → Cups too big

Side Test:

From the side, the entire breast should be contained within the cup
No "double boob" (flesh spilling over the top)
No fabric under the armpit

Apex Test:

The most prominent point of your breast should be in the center of the cup
If it's too low → Cups too big or band too loose
If it's too high → Straps too tight

Strap Test

Slipping Test:

The straps should stay in place on your shoulders
If they slip → Too loose or band too big

Comfort Test:

Slide one finger under the strap
You should be able to do so comfortably
If it digs in → Too tight or band too loose (all weight on straps)

Support Test:

Completely loosen the shoulder straps
The support should remain correct (80% comes from the band)
If everything falls → Band too large

Signs of an Incorrect Size

Band Too Large

Symptoms:

❌ Rides up in the back
❌ You can fit your whole hand underneath
❌ Moves when you raise your arms
❌ All the weight rests on your shoulders
❌ Painful marks from the straps

Solution: Go down one band size (and possibly up one cup size)

Band Too Small

Symptoms:

❌ Leaves deep marks on the skin (bulges)
❌ Difficulty breathing deeply
❌ Feeling of compression
❌ Redness under the breast
❌ Fastened on the last hook-and-eye from the start

Solution: Go up one band size (and possibly down one cup size)

Cups Too Small

Symptoms:

❌ Spillage at the top ("double boob")
❌ Spillage at the sides or under the arms
❌ The center gore does not lie flat against the sternum
❌ Unpleasant compression feeling
❌ Red marks on the chest

Solution: Go up one cup size (or down one band size if the band is too loose)

Cups Too Large

Symptoms:

❌ Empty space in the cup (wrinkles in the fabric)
❌ The breast "floats" in the cup
❌ The breast slides down in the cup
❌ No "enveloping" effect

Solution: Go down one cup size (or up one band size if the band is too tight)

Specifics by Model Type

Triangle Bralette

Sizing: Often in S/M/L/XL

Feature: More flexible, adapts better to variations

Tip: If between two sizes, choose the smaller one if you want support, the larger one if you prioritize comfort

Ideal for: A to C cups

Full-Coverage Wireless Bra

Sizing: Precise standard (85B, 90C...)

Feature: More rigid structure, less flexibility

Tip: Follow your calculated size exactly. Consult the brand's specific guide.

Ideal for: All cup sizes, especially C to F

Twinswomen Full-Coverage Collection →

Wireless Sports Bra

Sizing: Often in S/M/L/XL or numeric (1, 2, 3...)

Feature: Significant compression, technical fabric

Tip: If between two sizes, choose the larger one for daily use, the smaller one for intense sports

Ideal for: All cup sizes depending on the model

Wireless Bandeau Bra

Sizing: Variable (S/M/L or standard)

Feature: No straps, all support comes from the band

Tip: The band must be very snug (more so than with a classic model)

Ideal for: A to D cups maximum

Brand Size Guide

Twinswomen

Sizing: Standard French, true to size

Range: 80A to 105H depending on models

Feature: Fits true to size, follow your measurements

Models:

Comfort Bralette: 85A-100D
Full-Coverage Plus Size: 90D-105G
Lace Triangle Bra: 80A-95C
Sports Bra: XS-XXL

Tip: Consult the guide on each product page. If in doubt between two sizes, contact customer service.

See all available sizes →

Dim / Etam (France)

Sizing: Standard French

Feature: Some models run slightly large

Tip: If between two sizes, take the smaller one

UK Brands (Bravissimo, Panache, Freya...)

Sizing: UK system (pay attention to cup sizes)

Feature: Very precise, extensive range

Tip: Convert cup sizes correctly (DD UK = E FR)

US Brands (ThirdLove, Calvin Klein...)

Sizing: US system (often S/M/L/XL)

Feature: More flexible in sizing

Tip: Check the specific conversion chart

Common Mistakes to Avoid

❌ Mistake #1: Sticking to Your "Usual" Size

You may have been wearing the wrong size for years without knowing it. Always measure yourself before each purchase, especially for wireless bras.

80% of women wear the wrong size with underwire bras.

❌ Mistake #2: Neglecting Morphological Variations

Your size can vary depending on:

Weight (+/- 3-5 kg = possible change)
Menstrual cycle (pre-menstrual swelling)
Age (hormonal changes)
Pregnancy and breastfeeding

Measure yourself every 6-12 months.

❌ Mistake #3: Ordering Without Consulting the Specific Guide

Each brand has its specificities. Always consult the size guide provided by the manufacturer, even if you know your "usual" size.

❌ Mistake #4: Prioritizing Immediate Comfort Over Fit

A bra that is too large will feel ultra-comfortable in the fitting room... but won't provide any support. A good fit might feel "snug" for the first few seconds but quickly becomes normal.

The band should be firm upon purchase (it will stretch over time).

❌ Mistake #5: Not Trying Several Sizes

Order 2-3 close sizes if buying online:

Your calculated size
A sister size
A variant if between two measurements

Return those that don't fit. It's the only way to be sure.

❌ Mistake #6: Relying Solely on the Mirror

The mirror doesn't show:

How the band sits in the back
Pressure points that will appear after 2 hours
If the band rides up when you move

Test by moving: raise your arms, bend over, twist your torso.

Special Cases

Asymmetrical Breasts

Problem: One breast larger than the other (very common!)

Solution: Choose the size for the larger breast. Adjust the strap on the smaller side to compensate.

Recommended models: Triangle or bralette with possible asymmetrical adjustment.

Between Two Sizes

Situation: Your measurements fall exactly between two sizes.

For the band size:

If you have a small/medium bust → Take the smaller size (better support)
If you have a large bust → Take the larger size (more comfort)

For the cup size:

Between two cup sizes → Order both and test

After Weight Loss/Gain

Change of 3-5 kg: Check your measurements, the size may have changed

Change of 5-10 kg: New size almost certain

Change of +10 kg: Measure yourself imperatively

Pregnancy and Breastfeeding

Rapid evolution: Your bust constantly changes

Tip:

1st trimester: Your usual size or +1 cup
2nd-3rd trimester: +1 to 2 cups
Breastfeeding: Evolving models or multiple sizes

Opt for: Wireless nursing bras with evolving cups

Menopause

Hormonal changes: Volume and shape can vary

Tip: Measure yourself every 6 months, prioritize comfort

Recommended models: Wireless bras in soft materials (cotton, modal)

Buying Online: The Winning Strategy

Before Ordering

1. Take your precise measurements 2. Consult the brand's size guide 3. Read customer reviews (often mention sizing) 4. Check the return policy

The Multi-Size Technique

Order 3 sizes:

Your calculated size
A sister size (if band too tight/loose)
+1 cup or -1 cup (depending on doubt)

Example: If you calculate 90D, order:

90D (your size)
85E (if band too loose)
90E (if cup too small)

Try them at home: Keep the perfect one, return the others.

At Twinswomen

Advantages: ✅ Fast delivery in France and Europe ✅ Free returns within 30 days ✅ Expert customer service available ✅ Detailed size guide on each product page ✅ Customer reviews mentioning sizes

Order with free return →

Frequently Asked Questions

Is my wireless bra size the same as my underwire bra size?

Generally yes, but not always. Some wireless brands size slightly differently. Always measure yourself and consult the specific guide.

Should I measure with or without a bra?

Ideally shirtless for an exact measurement of your natural bust. If you prefer, wear a thin, non-compressive bralette (never a push-up or padded bra).

I measure 87 cm, is that an 85 or a 90?

87 cm is right in between. Order both sizes and test. Generally, opt for the 90 (larger size) for more comfort, especially if you have a medium to large bust.

Are sister sizes truly identical?

The cup volume is equivalent, but the band size differs. Comfort can therefore vary. It's an adjustment tool, not an "identical" size.

How long does a wireless bra last?

With proper care: 12 to 18 months (approximately 50 washes). Own several for rotation and to extend their lifespan.

Does size change with the menstrual cycle?

Yes, the bust can swell by 5 to 15% before menstruation. Measure yourself mid-cycle for an "average" size. Wireless bras, being more flexible, adapt better to these variations than underwire models.

What if my size doesn't exist in the model I want?

Option 1: Use a sister size Option 2: Contact the brand (some offer custom sizing) Option 3: Look for the same type of model from a brand with a wider range

Conclusion: The Perfect Size Exists!

Choosing the right wireless bra size is not an exact science, but by methodically following the steps in this guide, you maximize your chances of success from the first try.

Key Points to Remember

✅ Measure yourself precisely: band and bust measurements ✅ Calculate your size with conversion charts ✅ Consult the specific guide for each brand ✅ Test the fit with band, cup, and strap tests ✅ Use sister sizes in case of imperfect fit ✅ Order several sizes if buying online ✅ Re-measure yourself regularly (every 6-12 months)

Our Final Tip

Don't be discouraged if the first attempt isn't perfect. Finding THE ideal size might require 2-3 tries, but once found, the incomparable comfort of a well-fitting wireless bra will transform your daily life.

At Twinswomen, we offer free returns within 30 days and expert customer service to assist you in your choice. You have nothing to lose by trying!