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Bra Size & Fit Guide

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Bras Size & Fit Guide | Farnelli Fit Lab

Bras Size & Fit Guide

Let’s make bras super easy. You pick a few numbers. We show you a safe starting bra size. No stress. No confusion.

Smart Start

Tell us what you want. We will take you there right away. Pick one box below.

I want my bra size (fast)

We will find your starting size using two simple measurements. You only choose from dropdowns.

I want the right bra type

Use filters. We show what each bra type means in plain words.

My bra feels wrong

Spillage, gaps, straps slipping, band riding up… we fix it in minutes.

I want comfort (all day)

We will help you choose wireless and gentle options that still look nice.

I don’t know anything (help me)

Answer a few tiny questions

We will guide you step by step.

1) Do you know your band number already?

Band is the number part, like 34 or 36.

Simple checklist
  • You measured underbust (under the breasts).
  • You measured bust (the fullest part).
  • Your band feels snug and level (not painful).
  • No spillage and no empty gaps.

If something feels off, go to Fixes. We tell you exactly what to change.

Size Finder
Bra size = 2 parts
  • Band = the number (example: 34). It goes around your ribs.
  • Cup = the letter (example: C). It comes from: bust minus underbust.

You will not type anything. Just pick numbers from dropdowns, then tap a button.

1) Pick unit 2) Pick underbust 3) Pick bust 4) Tap button

Option A: I can measure underbust + bust (best)

Measure two places. That’s it.


Tape under your breasts, around your ribs. Snug and level.


Tape around the fullest part. Comfortable, not tight.


No tape measure?

Use a string or ribbon. Wrap, mark it, then measure that length with a ruler.

Option B: I already know my band number

Choose your band and your bust. We estimate the cup letter.

Example: 30, 32, 34, 36, 38…



Comfort rule

The band does most of the support. Straps help, but the band is the main support.

Fit Rules

The 5 easy rules

  • Band stays level: straight across your back. Snug, not painful. (Two fingers fit.)
  • Cups look smooth: no spilling out, and no empty space.
  • Center sits flat (wired bras): the middle touches your chest.
  • Straps feel gentle: they should not dig or leave deep marks.
  • Wire sits around breast tissue: not on top of it.
Spilling out = cup up Band rides up = band down Gap = cup down or style change

How to measure

Underbust (snug)
Tape under breasts, around ribs. Snug and level. This helps choose the band.
Bust (fullest)
Tape around the fullest part. Comfortable, not tight. Keep it level.
Scoop & swoop
After you put the bra on, gently move all breast tissue into the cups. This improves fit.

Charts
International Size Converter (one line)

Choose the system on your bra tag, then choose band and cup. We show the closest matches.

Small note

If the band feels different from what you expect, use sister sizing below.

Charts made easy

Three steps:

1) Band

Band is the number. Use the first table to match US/UK/EU.

2) Cup

Cup comes from: bust minus underbust.

3) Adjust

If cups feel fine but the band feels wrong, use sister sizing.

Band = snug + level Cup = smooth Comfort matters
Band Conversion (US / UK / EU)

Same body, different labels.

US UK EU
Cup Difference Chart (Bust − Underbust)
Cup is a difference

We take two numbers: bust minus underbust. The difference gives the cup.

36 − 34 = 2 → B 41 − 36 = 5 → DD/E
Difference Cup Difference (cm approx) Easy note
Sister Sizing (super clear + calculator)
Use this only for the band

Sister sizing is for one situation: the cups feel fine, but the band feels wrong.

The rule (one line)

Band up 1 step → cup down 1 step
Band down 1 step → cup up 1 step

34D → 36C 34D → 32DD/E 32C → 34B 36DD/E → 34DDD/F
Sister Size Calculator

Choose your current size, then tap the button that matches how the band feels.

Do not use sister sizing if cups are wrong
  • If you have spillage, go up in cup.
  • If you have gaps, go down in cup or change style.

Bra Types

This is an all-inclusive list of common bra types you will see when shopping. Each one is explained in simple words. Use filters to find what you need.

T-Shirt Bra

Smooth and clean under tops. The easiest everyday bra.

SmoothEverydayEasy

Full Cup Bra

More coverage. Holds everything in securely. Great for support.

SupportMore coverageSecure

Full Coverage Bra

Coverage-focused. Helps reduce spillage. Comfortable for long wear.

SecureEverydayComfort

Demi Bra

A bit more open on top. Nice under lower-cut tops.

NecklineEverydayFlattering

Balconette Bra

Lift + rounded look. Great with square or wide necklines.

LiftStyleShape

Plunge Bra

Lower center front. Best for deep necklines.

Deep necklineDressyLow front

Bralette

Wireless and comfy. Gentle support. Great for relaxing days.

WirelessComfortEasy

Strapless Bra

No straps. Strong band helps it stay up. Best for strapless outfits.

StraplessEventSmooth

High-Impact Sports Bra

Strong hold for running and jumping.

High supportActiveHold
Safe pick

If you are unsure: pick a snug band. Then adjust the cup: spillage = cup up, gaps = cup down or style change.

Fixes

Pick your problem below. We tell you what to change.

Band rides up your back
Band is too big. Go down a band size. If cups feel tight after that, go up a cup (sister sizing rule).
Straps keep slipping
Try racerback or convertible. Also check the band. A loose band makes straps work too hard.
Spillage (top or sides)
Cup is too small or the style is too open. Go up one cup, or choose fuller coverage.
Gaping (empty space) at the top
Cup may be too big or the shape is not right. Try one cup down, or try a different style.
Center does not sit flat (wired bras)
Often the cup is too small. Try one cup up.
Underwire hurts
Wire may be on breast tissue. Often the fix is a bigger cup. Or choose wireless for comfort.
Band feels painfully tight
Use sister sizing: band up and cup down. Also start wearing on the loosest hook.

FAQ
What is the #1 bra mistake?
Band too big and cups too small. The band should do most of the support.
How do I know my cup is too small?
Spillage, center not flat (wired bras), or wire sits on breast tissue.
How tight should the band be?
Snug and level. Not painful. Two fingers can fit under it.
Which hook do I start with?
Start with the loosest hook. Tighten later as the band stretches over time.

Glossary

Small dictionary. Search a word here.

Band

The part that wraps around your ribs. It should be snug and do most of the support.

FitEasy

Cup

The part that holds your breast. Spillage means cup up. Empty space means cup down or a different style.

FitEasy

Sister Size

Use when cups feel fine but band feels wrong. Band up means cup down. Band down means cup up.

FitEasy

Underwire

A wire under the cup. It adds lift. It should sit around breast tissue, not on it.

SupportEasy

Gore

The center piece between the cups. In wired bras, it often should touch your chest.

Fit

Adjustable Straps

Straps you can shorten or lengthen. Straps help, but the band is the main support.

FeaturesEasy

Plunge

Lower center front. Works with deep necklines.

StyleEasy

Balconette

A lift style with a more open top edge and wider-set straps.

Style

Seamless

Made to look smooth under clothing with fewer lines showing.

FabricEasy

Padding / Lining

Material in the cup for shape or modesty. Light lining feels natural. Push-up adds extra lift.

Features

Racerback

Straps meet in the center back. Helps stop straps from slipping.

StyleEasy

Unlined

No padding. More natural feel. Often more breathable.

FabricEasy
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