Find your perfect bra size with our intuitive and accurate measurement tool.
Measure and Calculate
Measure snugly around your rib cage, directly under your bust. Keep the tape measure level.
Measure loosely around the fullest part of your bust, keeping the tape measure parallel to the ground.
Standard (e.g., T-shirt, Full Cup)
Balconette/Demi-Cup
Plunge
Sports Bra
Different bra styles can affect perceived fit and measurement requirements.
UK Sizing
US Sizing
EU Sizing
Select your preferred bra sizing system.
Your Bra Size Results
—
Band Size: —
Cup Size: —
Sister Size: —
How it's Calculated: The band size is typically determined by your underbust measurement, with adjustments made for different sizing systems. The cup size is calculated by finding the difference between your bust measurement and your band measurement. This difference, when mapped to a specific sizing system, reveals the cup letter. Sister sizes are bra sizes that share the same cup volume but have different band and cup measurements, useful for fine-tuning fit. Different bra types might require slight variations in measurement or calculation, especially for plunge or sports bras.
Measurement Chart
Measurement
Metric
Range
Underbust
cm
50 – 120
Bust
cm
60 – 150
Input your underbust and bust measurements in centimeters for accurate sizing.
Size Distribution Chart
Visual representation of common bra sizes and their components (band vs. cup).
What is a Bra Soze Calculator?
A bra soze calculator is an online tool designed to help individuals determine their most accurate bra size. Unlike generic sizing guides that rely on broad estimations, a bra soze calculator uses specific measurements taken from the body to provide a precise, personalized bra size recommendation. This tool is crucial because many people wear ill-fitting bras, which can lead to discomfort, poor support, and even long-term health issues. The primary goal of a bra soze calculator is to simplify the often confusing process of bra shopping by offering a data-driven approach.
This calculator is intended for anyone who wears bras and seeks a better fit. This includes individuals who are:
Purchasing a new bra, especially online.
Experiencing discomfort or poor fit with their current bras.
Undergoing body changes (e.g., weight fluctuations, pregnancy, hormonal changes).
Confused by the various international sizing systems (UK, US, EU, etc.).
Seeking to understand their body measurements better in relation to apparel sizing.
A common misconception is that a single measurement is sufficient for determining bra size, or that bra sizes are universal across all brands and regions. In reality, bra sizing is complex, influenced by many factors including brand variations, bra styles, and the chosen measurement system. Another misconception is that bra size remains constant throughout life; body composition changes mean regular re-measurement is often necessary. The bra soze calculator aims to dispel these myths by emphasizing accurate, multi-point measurements and acknowledging sizing variations.
Bra Soze Calculator Formula and Mathematical Explanation
The core of any bra soze calculator lies in its formula, which converts body measurements into a standardized bra size. While specific algorithms can vary slightly between calculators and sizing systems, the fundamental principles remain consistent. The process typically involves two primary measurements: the underbust (band size) and the bust (cup size determination).
Step 1: Determine the Band Size
The underbust measurement is the primary determinant of the bra's band size. This measurement is taken snugly around the rib cage, directly beneath the bust line.
Step 2: Calculate the Cup Size Difference
The bust measurement is taken around the fullest part of the chest, typically over the nipples. The difference between the bust measurement and the underbust measurement is calculated.
Step 3: Convert Difference to Cup Letter
This difference is then translated into a cup size (e.g., A, B, C, D) based on specific increments defined by the chosen sizing system (UK, US, EU). Each cup size typically corresponds to a fixed increase in measurement difference.
Step 4: Apply Sizing System Adjustments
Different regions use different sizing standards. For example, UK and US sizing systems have distinct band and cup size mappings. European (EU) sizing often uses centimeter differences directly or has its own unique scale. A sophisticated bra soze calculator accounts for these variations based on user selection.
Step 5: Calculate Sister Sizes
Sister sizes are a crucial concept for fine-tuning fit. A sister size shares the same cup volume but has a different band size. If a size feels too tight in the band but the cup fit is good, you move to a larger band and smaller cup (e.g., 34C to 36B). If the band is too loose but the cup fit is good, you move to a smaller band and larger cup (e.g., 34C to 32D). The relationship is typically: Band Size + 2 inches (or ~5 cm) corresponds to a cup size down, and Band Size – 2 inches (or ~5 cm) corresponds to a cup size up.
Formula Breakdown:
Let:
U = Underbust Measurement (cm)
B = Bust Measurement (cm)
D = Bust-Underbust Difference (cm) = B – U
Band Size Calculation (Simplified Example for EU/UK based on common ranges):
The underbust measurement is often mapped to a specific band size. For example, in some systems:
63-67 cm ≈ 65 band
68-72 cm ≈ 70 band
73-77 cm ≈ 75 band
78-82 cm ≈ 80 band
83-87 cm ≈ 85 band
And so on…
Note: US sizing often uses inches, and there might be specific band size charts for each system.
Cup Size Calculation (Simplified Example for EU/UK based on difference):
The difference D is mapped to cup sizes. Increments vary by system and sometimes by band size. A common approximation (not universally exact):
D ≈ 10-12 cm = A Cup
D ≈ 12-14 cm = B Cup
D ≈ 14-16 cm = C Cup
D ≈ 16-18 cm = D Cup
D ≈ 18-20 cm = DD/E Cup
And so on…
US sizing often uses inch differences and different cup letter progressions.
Sister Size Calculation:
If calculated size is Band X, Cup Y:
Next larger band size (e.g., 75 to 80) typically corresponds to one cup size smaller (e.g., C to B).
Next smaller band size (e.g., 75 to 70) typically corresponds to one cup size larger (e.g., C to D).
Variables Used in Bra Size Calculation
Variable
Meaning
Unit
Typical Range
Underbust Measurement
Circumference around the ribcage directly below the bust.
cm / inches
50 – 120 cm (20 – 47 inches)
Bust Measurement
Circumference around the fullest part of the bust.
cm / inches
60 – 150 cm (24 – 59 inches)
Bust-Underbust Difference
The difference between bust and underbust measurements, indicating cup volume.
cm / inches
0 – 50+ cm (0 – 20+ inches)
Band Size
The numerical part of the bra size, related to underbust measurement.
Numeric (e.g., 70, 75, 34, 36)
Varies widely by system
Cup Size
The alphabetical part of the bra size, indicating cup volume relative to band size.
Letter (e.g., A, B, C, D)
A, B, C, D, DD, E, F, G…
Sister Size
A bra size with the same cup volume but a different band size.
Band Size + Cup Size
e.g., 36B, 38C, 34D
Practical Examples (Real-World Use Cases)
Example 1: Finding a Standard Fit
Scenario: Sarah measures her underbust at 74 cm and her bust at 91 cm. She prefers a standard T-shirt bra and wants to know her UK size.
Inputs:
Underbust Measurement: 74 cm
Bust Measurement: 91 cm
Bra Type: Standard
Calculation Mode: UK Sizing
Calculation:
Band Size Calculation: 74 cm falls into the 75 band range (assuming common EU/UK band increments).
Bust-Underbust Difference: 91 cm – 74 cm = 17 cm.
Cup Size Determination (UK): A 17 cm difference typically corresponds to a C cup in UK sizing (e.g., 12-14cm=B, 14-16cm=C, 16-18cm=D. The exact chart may vary slightly).
Outputs:
Primary Result: 75C
Band Result: 75
Cup Result: C
Sister Sizes: 70D, 80B
Interpretation: Sarah's calculated UK bra size is 75C. The sister sizes 70D and 80B offer alternative fits with the same cup volume if the 75C doesn't feel quite right. She should try the 75C first. If the band feels too loose, she might try the 70D. If the band feels too tight, she might try the 80B.
Example 2: Adjusting for a Different Sizing System
Scenario: John's partner, Maria, measured her underbust at 81 cm and her bust at 105 cm. She's unsure if her current US size 36D is correct and wants to see her EU size.
Inputs:
Underbust Measurement: 81 cm
Bust Measurement: 105 cm
Bra Type: Standard
Calculation Mode: EU Sizing
Calculation:
Band Size Calculation (EU): 81 cm falls into the 80 band range.
Bust-Underbust Difference: 105 cm – 81 cm = 24 cm.
Cup Size Determination (EU): A 24 cm difference typically corresponds to an F cup in EU sizing (e.g., 12cm=A, 14cm=B, 16cm=C, 18cm=D, 20cm=E, 22cm=F, 24cm=G. This calculator uses standard increments). Given the difference, it might map to a G or H cup depending on specific chart. Using a common chart: 22-24cm = G cup.
Important Note: Different brands and regions have slightly different mappings. For a 24cm difference, EU sizing can sometimes map to G or H. This calculator will use standard increments. Let's assume for this example the calculator maps 22-24cm difference to a G cup.
Outputs (assuming G cup for 24cm difference):
Primary Result: 80G
Band Result: 80
Cup Result: G
Sister Sizes: 75H, 85F
Interpretation: Maria's calculated EU bra size is 80G. Her current US size 36D might not be the best fit. A US 36 band is roughly equivalent to an EU 80 band. However, a US D cup is typically equivalent to an EU DD (or E) cup. Her calculated 24cm difference suggests a much larger cup size (EU G) than her current US D cup implies. This indicates her current bra might be too small in the cup. The sister sizes 75H and 85F are also worth considering if 80G isn't perfect. This example highlights the critical importance of using the correct bra soze calculator and understanding different sizing systems.
How to Use This Bra Soze Calculator
Using the bra soze calculator is straightforward. Follow these steps for the most accurate results:
Gather Your Tools: You'll need a flexible measuring tape (preferably in centimeters) and a mirror. Ensure the tape measure is not stretched.
Measure Underbust: Stand up straight and place the tape measure snugly around your rib cage, directly under your bust. Ensure the tape is level all the way around. Note this measurement in centimeters. This is your Underbust Measurement.
Measure Bust: Now, measure around the fullest part of your bust (usually over the nipples). Keep the tape measure parallel to the ground and ensure it's not too tight or too loose. This is your Bust Measurement.
Select Bra Type: Choose the style of bra you typically wear or are looking to purchase from the dropdown menu. This can sometimes influence fit recommendations.
Choose Sizing System: Select your preferred sizing system (UK, US, EU). If you're unsure, UK or EU are often considered more consistent.
Input Measurements: Enter your recorded underbust and bust measurements into the respective fields in the calculator.
Calculate: Click the "Calculate Size" button.
How to Read Results:
Primary Result: This is your most likely bra size (e.g., 75C).
Band Size: The numerical component of your bra size.
Cup Size: The alphabetical component, indicating volume.
Sister Sizes: These are alternative sizes that have the same cup volume but different band sizes. They are invaluable for fine-tuning the fit. If your primary size feels slightly off in the band, try a sister size. For example, if 75C feels too tight in the band, try 80B (larger band, smaller cup). If it feels too loose, try 70D (smaller band, larger cup).
Decision-Making Guidance:
Always try the primary calculated size first.
Use sister sizes as a secondary option if the primary size isn't perfect.
Pay attention to how the bra feels: the band should be snug and parallel to the ground, the cups should fully contain the breast tissue without gaping or spilling, and the straps should be comfortable.
If you're between sizes or experiencing persistent fit issues, consider consulting a professional bra fitter or trying bras from brands known for consistent sizing. This bra soze calculator provides a strong starting point.
Key Factors That Affect Bra Soze Results
While a bra soze calculator uses objective measurements, several subjective and external factors can influence the final fit and the perceived accuracy of the result. Understanding these is key to finding a truly comfortable and supportive bra.
Brand Variations: This is perhaps the most significant factor. Bra sizing is not standardized across all brands. A 75C in one brand might fit very differently from a 75C in another. Different brands use slightly different measurement charts, wire widths, cup depths, and band tightness. Always check brand-specific size guides if available.
Bra Style and Design: The cut and construction of a bra heavily impact fit. A plunge bra will fit differently than a full-cup or balconette style, even in the same size. Sports bras often require a firmer, more compressive fit, potentially necessitating a different size than everyday bras. Our calculator allows selection of bra type to acknowledge this.
Body Composition and Shape: Individual breast shape (e.g., teardrop, conical, round) and density play a role. Bra construction is often optimized for certain shapes. Tissue elasticity and how it settles over time can also affect fit. Some people have significant asymmetry between breasts.
Measurement Accuracy: Even slight inaccuracies in taking the underbust or bust measurements can lead to a different size recommendation. The tape measure needs to be held correctly – snug but not digging in for the underbust, and parallel without significant pressure for the bust.
Under-Or-Over-Sizing of Previous Bras: If you've consistently worn bras that are too large in the band or too small in the cup, your body might have adapted or you might be accustomed to a poor fit. This can make a correctly calculated size feel unusual initially. This is why understanding sister sizes is important.
Changes in Body Weight and Hormones: Fluctuations in weight, pregnancy, breastfeeding, and hormonal cycles (like menstruation) can cause temporary or permanent changes in breast size and shape. Regular re-measurement using a tool like this bra soze calculator is advisable, especially during these times.
Material and Elasticity: The fabric composition and the stretch of the bra material influence how it conforms to the body. Older bras lose elasticity, making the band feel looser than it should. New bras might feel firmer.
Frequently Asked Questions (FAQ)
How often should I measure my bra size?
It's generally recommended to measure your bra size at least once a year, or more frequently if you experience significant body changes such as weight fluctuations, pregnancy, or hormonal shifts. Even without major changes, bras can lose elasticity over time, affecting fit.
Why does my bra size differ between brands?
Bra sizing is notoriously inconsistent across brands. Each manufacturer may have its own specific sizing charts, patterns, and interpretations of measurements. This is why a bra soze calculator provides a starting point, but trying on bras from different brands is essential.
What does "sister size" mean and how do I use it?
Sister sizes are bra sizes that share the same cup volume but have different band measurements. For example, 34C, 36B, and 32D are sister sizes. If a bra fits well in the cup but the band is too tight, you go up a band size and down a cup size (e.g., 34C to 36B). If the band is too loose, you go down a band size and up a cup size (e.g., 34C to 32D). Our bra soze calculator provides these.
Is it okay if my breasts are different sizes?
Yes, it's very common for one breast to be slightly larger than the other. In this case, you should size your bra to fit the larger breast. You can then use pads or inserts in the cup of the smaller breast, or adjust the straps on the smaller side if possible, to achieve a better fit.
My underbust measurement is exactly on a band size line. What should I do?
If your underbust measurement falls exactly on the border between two band sizes, it's often recommended to size up in the band for a less compressive fit, especially if you prefer comfort. However, if you prefer a very snug band, you might size down. Trying both sizes is ideal. Many find that the calculator's suggestion for band size is a good starting point.
What if the calculator gives me a size I've never heard of before?
It's possible! Many people wear sizes that aren't commonly stocked or discussed. Don't be discouraged. Use the sister size feature to find more commonly available sizes that might still offer a good fit. Researching brands that cater to a wider range of sizes can also be helpful. This bra soze calculator aims for accuracy beyond common assumptions.
Can bra fit affect my posture or cause pain?
Absolutely. A bra that is too small in the cup or too loose in the band offers inadequate support. This can cause breasts to pull on the shoulders and back, leading to discomfort, neck pain, back pain, and poor posture over time. Proper support from a well-fitted bra is crucial for comfort and health.
What's the difference between UK, US, and EU bra sizing?
The primary differences lie in how band sizes are numbered and how cup size increments are measured. UK and US band sizes are often based on inches (though cm are used for calculations), with different progressions. Cup sizes also differ; for example, a UK D cup is smaller than a US D cup, and EU sizing often uses a different scale entirely, sometimes with double cup sizes (like FF, GG). Our bra soze calculator helps convert between these.