Reddit Bra Size Calculator
Discover your accurate starting size with the method popularized by the r/ABraThatFits community.
Select the unit you used for your measurements.
Tape is comfortably loose around your ribcage.
Tape is snug, as a new bra band should feel.
Tape is as tight as possible, after exhaling fully.
Tape around the fullest part of your bust while standing straight.
While leaning forward at 90 degrees, measure around the fullest part.
While lying on your back, measure around the fullest part.
Your Starting Size Is…
This is a starting point. Fit can be affected by breast shape and bra style.
Your Measurements Visualized
This chart shows the relationship between your three bust measurements, which indicates breast projection.
Sister Size Options
| Tighter Band, Larger Cup | Your Starting Size | Looser Band, Smaller Cup |
|---|---|---|
| — | — | — |
What is the Reddit Bra Size Calculator?
The reddit bra size calculator refers to a specific method of determining a starting bra size that gained widespread popularity on the Reddit community r/ABraThatFits. Unlike traditional methods that often add 4 or 5 inches to the underbust measurement (an outdated practice from when bras had no stretch), this calculator uses six precise measurements to account for variations in body composition and breast shape. It is considered one of the most accurate online methods for finding a reliable starting point for your bra size journey.
This calculator is for anyone who has struggled with poorly fitting bras—gapping cups, slipping straps, or a band that rides up. By using a more detailed set of measurements, it provides a size that is much more likely to offer proper support and comfort. Even if the resulting size seems surprising (a common experience known as “sticker shock”), it is a valuable first step. From here, you can explore related sizes and styles to find your perfect fit. The first step is often learning about the difference between US and UK bra sizing.
Reddit Bra Size Calculator Formula and Explanation
The logic behind the reddit bra size calculator is more nuanced than a simple subtraction. It uses multiple measurements to create a more accurate and personalized recommendation. Here’s a breakdown of the process:
- Band Size Calculation: The band size is primarily determined by your underbust measurements. This calculator often uses the snug underbust measurement and rounds it to the nearest even number. For example, a snug measurement of 31.2 inches would round to a 32 band. Some versions, like this one, may also consider the loose underbust for comfort.
- Bust Measurement Calculation: To account for breast shape and tissue distribution, an average of the three bust measurements (standing, leaning, and lying) is used. The leaning measurement is particularly important as it helps capture the full volume of projected breasts.
- Cup Size Calculation: The cup size is found by subtracting the calculated band size from the averaged bust measurement. Each inch of difference corresponds to a cup letter. For instance, a 3-inch difference is a C cup, a 4-inch difference is a D cup, and so on.
The final size is your UK size, as UK sizing is more consistent across brands, especially in larger cup sizes. If you need help with sizing, check out this bra fitting guide for more information.
| Variable | Meaning | Unit | Typical Range |
|---|---|---|---|
| Underbust | Measurement of the ribcage directly beneath the breasts. | in/cm | 24 – 50 in |
| Bust | Average measurement of the fullest part of the breasts. | in/cm | 28 – 65 in |
| Cup Difference | Calculated Bust – Calculated Band Size | inches | 1 – 20 in |
Practical Examples
Example 1: Average Projection
- Inputs (inches): Loose 30, Snug 29, Tight 28, Standing 35, Leaning 37, Lying 36
- Calculation:
- Band Size: Rounds from snug underbust (29) to a 30 band.
- Average Bust: (35 + 37 + 36) / 3 = 36 inches.
- Cup Difference: 36 (avg bust) – 30 (band) = 6 inches.
- Result: A 6-inch difference corresponds to an E cup in UK sizing. The starting size is 30E UK.
Example 2: Projected Shape
- Inputs (inches): Loose 34, Snug 33.5, Tight 32, Standing 40, Leaning 44, Lying 42
- Calculation:
- Band Size: Rounds from snug underbust (33.5) to a 34 band.
- Average Bust: (40 + 44 + 42) / 3 = 42 inches.
- Cup Difference: 42 (avg bust) – 34 (band) = 8 inches.
- Result: An 8-inch difference corresponds to a FF cup in UK sizing. The starting size is 34FF UK. Exploring sister sizes might also be beneficial.
How to Use This Reddit Bra Size Calculator
- Select Your Units: Start by choosing whether you measured in inches or centimeters. The calculator will handle the conversion.
- Enter Your Six Measurements: Carefully input the six measurements into their respective fields. For best results, use a soft measuring tape and measure while unclothed or wearing a non-padded bra.
- View Your Starting Size: The calculator will instantly display your estimated starting size in both UK and US sizing systems. The UK size is often recommended as a more standardized starting point.
- Check Intermediate Values: The results area shows your calculated band size and total bust circumference, which helps you understand how the final size was derived.
- Consult the Sister Size Table: If your recommended band feels too tight or loose, the sister size table provides alternatives with the same cup volume. Knowing the difference between US and UK bra sizes is key.
Key Factors That Affect Bra Fit
Your calculated size is an excellent starting point, but it’s not the end of the journey. Several other factors play a crucial role in finding the perfect bra. If you’re having issues, you may need a bra size converter.
- Breast Shape: Are your breasts full on top, full on bottom, or evenly distributed? Different bra styles (e.g., balconette, plunge, full cup) are designed to accommodate different shapes.
- Breast Projection: This refers to how far your breasts stick out from your chest. Projected breasts often need bras with deeper cups, while shallow shapes are better suited to bras with wider, less deep cups. The difference between your standing and leaning bust measurements is a good indicator of projection.
- Breast Root Width: The “root” is where your breast tissue attaches to your chest wall. Some people have wide roots (tissue extends towards the armpits), while others have narrow roots. The underwire of a bra should comfortably encase your entire root without digging in.
- Tissue Density: Firm, self-supporting breast tissue may fit differently than softer tissue, which is more malleable and can fill out different cup shapes.
- Band Firmness: Different brands use materials with varying degrees of stretch. You may need to go up or down a band size depending on the specific bra’s construction, which is where understanding sister sizes becomes very useful.
- Asymmetry: Most people have one breast that is slightly larger than the other. Always fit to the larger breast and use pads or inserts to fill the gap on the smaller side if necessary.
Frequently Asked Questions
- Why is my calculated size so different from what I wear now?
- This is very common! Most stores use outdated fitting methods that put people in a very limited range of sizes (e.g., a 34B or 36C). The reddit bra size calculator avoids adding inches to the band, which typically results in a smaller band and a larger cup size for better support.
- What’s the difference between UK and US sizing?
- Band sizes are the same (a 32 band is a 32 band). However, cup sizes diverge after DD. A UK DD is the same as a US DD. But a UK E is a US DDD/F, a UK F is a US G, and so on. Our calculator provides both for clarity.
- What are sister sizes?
- Sister sizes are bras with the same cup volume but different band and cup letter combinations. To find a sister size, you can go up one band size and down one cup letter (e.g., 32D -> 34C) or down one band size and up one cup letter (e.g., 32D -> 30DD). This is useful if the cups fit well but the band doesn’t.
- My measurements are in centimeters. Does this work?
- Yes. Select “Centimeters (cm)” from the unit dropdown. The calculator will convert your measurements to inches internally to perform the calculation, as the standard inch-based cup progression is the industry norm.
- The calculator gave me a size like 30G. I’m not that big! What gives?
- Cup size is relative to band size. A G cup on a 30 band is much smaller than a G cup on a 40 band. Societal perception of what a “G cup” looks like is often skewed. Trust the measurements as a starting point and try on the recommended size. You might be surprised!
- Which measurement is most important?
- All six are important for an accurate result, but the snug underbust and leaning bust are arguably the most critical. The snug underbust is key for a supportive band, and the leaning bust helps ensure the cup has enough volume to prevent spillage.
- How often should I re-measure?
- It’s a good idea to re-measure every 6-12 months, or after any significant weight changes, pregnancy, or hormonal shifts, as these can all affect your bra size.
- What if I’m between two sizes?
- This is normal! The calculator provides a *starting* point. If you are between sizes, consider your breast shape and the type of bra you are buying. You may need to try both sizes to see which offers a better fit. Many people find they wear slightly different sizes in different brands or styles.