A Bra That Fits (ABTF) Reddit Calculator

The definitive tool for finding your true bra size based on the /r/ABraThatFits community method.

Underbust Measurements

Bust Measurements

Your Estimated Starting Size

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UK Sizing System

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Calculated Band

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Calculated Cup

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Bust-Band Difference

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Average Bust

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Sister Sizes to Try

Go up a band, down a cup: —

Go down a band, up a cup: —

Understanding the A Bra That Fits Reddit Calculator

The a bra that fits reddit calculator is a revolutionary tool for individuals seeking a comfortable and supportive bra. It stems from the collective knowledge of the /r/ABraThatFits community on Reddit, a group dedicated to debunking common bra fitting myths. Unlike traditional methods that often incorrectly add inches to the band measurement (the “+4 method”), this calculator uses six precise measurements to provide a much more accurate starting point for your bra size.

This method is for anyone who has struggled with common fit issues like gaping cups, slipping straps, a riding-up band, or painful underwires. By using a more data-driven approach, the a bra that fits reddit calculator helps you understand your body’s unique shape and volume, empowering you to find a bra that truly fits.

The A Bra That Fits (ABTF) Formula and Explanation

The core logic of the a bra that fits reddit calculator is based on two key principles: the band size is determined by your underbust measurement, and the cup size is determined by the difference between your bust and underbust measurements. The use of multiple measurements provides a more accurate picture of breast volume and shape.

Formula Steps:

1. Determine Band Size: The band size is typically your snug underbust measurement, rounded to the nearest even number. For example, a 29.5″ snug underbust would be a 30 band.
2. Calculate Average Bust Circumference: This accounts for how breast tissue is distributed.
   
   Average Bust = (Standing Bust + Leaning Bust + Lying Bust) / 3
3. Calculate Cup Volume Difference: The difference between your average bust and your snug underbust determines the cup volume.
   
   Cup Difference = Average Bust – Snug Underbust
4. Convert Difference to Cup Size: Each inch of difference corresponds to a cup letter in the UK sizing system. This is the most crucial step where the ABTF method differs from mainstream sizing.

UK Cup Size Conversion (Inches)

Difference (in)	UK Cup Letter	Difference (in)	UK Cup Letter
1″	A	9″	G
2″	B	10″	GG
3″	C	11″	H
4″	D	12″	HH
5″	DD	13″	J
6″	E	14″	JJ
7″	F	15″	K
8″	FF	16″	KK

For help with sizing, check out our guide on understanding breast shape.

Practical Examples

Example 1: Smaller Band, Larger Cup

• Inputs (Inches): Loose Underbust: 29.5, Snug: 29, Tight: 28, Standing Bust: 35, Leaning: 37, Lying: 36
• Band Calculation: Snug underbust is 29″. Rounded to the nearest even number is 30. Band Size = 30.
• Bust Calculation: Average Bust = (35 + 37 + 36) / 3 = 36″.
• Cup Calculation: Cup Difference = 36″ (Avg Bust) – 29″ (Snug Underbust) = 7″.
• Result: A 7″ difference corresponds to an F cup. The starting size is 30F in UK sizing.

Example 2: Larger Band, Moderate Cup

• Inputs (Inches): Loose Underbust: 38, Snug: 37.5, Tight: 36, Standing Bust: 43, Leaning: 45, Lying: 44
• Band Calculation: Snug underbust is 37.5″. Rounded to the nearest even number is 38. Band Size = 38.
• Bust Calculation: Average Bust = (43 + 45 + 44) / 3 = 44″.
• Cup Calculation: Cup Difference = 44″ (Avg Bust) – 37.5″ (Snug Underbust) = 6.5″.
• Result: A 6.5″ difference is between an E (6″) and F (7″). The calculator will often suggest the larger size as a start, so a UK 38F is a good starting point.

How to Use This A Bra That Fits Reddit Calculator

1. Select Your Units: Choose between Inches (in) or Centimeters (cm). The calculator automatically converts everything for accurate calculation.
2. Take Your 6 Measurements: Use a soft measuring tape. For best results, do not wear a padded or molded bra. Ensure the tape is parallel to the floor for all measurements.
3. Enter the Values: Input each of your six measurements into the corresponding fields.
4. View Your Result: The calculator instantly provides your estimated starting size in the UK sizing system. This system is used by the ABTF community for its consistency. You can find more details in our UK vs. US sizing guide.
5. Consider Sister Sizes: The calculator also provides sister sizes. If the recommended band feels too tight or loose, you can try a sister size to find a better fit while maintaining the same cup volume.

Key Factors That Affect Bra Fit

The a bra that fits reddit calculator gives you an excellent starting point, but it’s not the final word. Several other factors are crucial for finding the perfect bra.

• Breast Shape: Are your breasts projected or shallow? Full on top or full on bottom? Different bra styles (e.g., balconette, plunge, full cup) are designed for different shapes. See our bra style guide for different shapes.
• Root Width: This refers to how wide the base of your breast is on your chest. A bra with underwires that are too narrow will poke, while wires that are too wide won’t provide proper support.
• Tissue Density: Softer breast tissue may be more malleable and fit into a wider range of cup shapes, while firmer tissue requires a more precise match.
• Brand and Style Variation: Just like with clothing, bra sizing is not standardized across brands. A 30F from one brand might fit differently than a 30F from another. Always be prepared to try a few sizes.
• Your Menstrual Cycle: Hormonal fluctuations can cause breasts to swell, sometimes by a full cup size or more. What fits perfectly one week might feel tight the next.
• The Age of Your Bra: As you wear and wash a bra, the band stretches out. A new bra should feel firm on the loosest hook; as it ages, you’ll move to the tighter hooks to maintain support.

Frequently Asked Questions (FAQ)

1. Why is the calculated size so different from my current size?

Most commercial stores use the outdated “+4 method,” which adds 4-5 inches to the underbust measurement. This artificially inflates the band size and deflates the cup size, leading to poor support. The a bra that fits reddit calculator bypasses this, often resulting in a smaller band and larger cup size that provides significantly better support.

2. Is the UK sizing system the same as the US system?

No, they differ, especially after a D cup. The UK system is more consistent: D, DD, E, F, FF, G, etc. The US system is often inconsistent: D, DD/E, DDD/F, G. This calculator uses the UK system as its standard. Learn more with our sizing conversion chart.

3. What if I’m between two sizes?

It’s very common. Use the calculated size as your starting point. Then, try the sizes directly above and below it, as well as the sister sizes. Your breast shape might mean you need to go up or down a cup size in a particular style.

4. Can I use this calculator if I’ve had a mastectomy or have asymmetrical breasts?

Yes, but with modifications. For asymmetry, measure to fit the larger breast. You can use an insert or “cutlet” to fill the cup on the smaller side. For post-mastectomy fitting, the measurements can still provide a starting band size, but cup fit will depend on whether you use a prosthesis.

5. Why are there three bust measurements?

Gravity and tissue distribution affect breast shape. The leaning measurement often captures the most accurate volume for projected breasts, while the lying measurement can be more accurate for shallow shapes. Averaging them provides a balanced estimate for the calculator.

6. My band measurement is an odd number. What do I do?

The calculator automatically rounds to the nearest even number, as bra bands are typically sold in even sizes (30, 32, 34, etc.). For example, a 31″ snug underbust would start with a 32 band.

7. Should the measuring tape be tight?

It depends on the measurement. “Loose” should be just touching the skin. “Snug” should be firm and parallel to the floor, like a well-fitting bra band. “Tight” should be as tight as you can pull the tape after exhaling, which helps determine how much stretch you need in a band.

8. Does this calculator work for sports bras or bralettes?

It provides a great baseline. However, sports bras and bralettes often use S/M/L sizing. Use your calculated size (e.g., 34G) to check the brand’s size chart to see which S/M/L size corresponds to your bra size. Check our recommendations for the best sports bras for high-impact activity.