abrathatfits calculator

The definitive tool for finding your starting bra size based on the /r/ABraThatFits methodology.

Your Recommended Starting Size

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Sister Size (Tighter Band): —

Sister Size (Looser Band): —

Enter all six measurements to see your result. Sizes are based on UK sizing.

What is the abrathatfits calculator?

The abrathatfits calculator is a sophisticated sizing tool based on the measurement method popularized by the Reddit community /r/ABraThatFits. Unlike traditional methods that often add 4-5 inches to the underbust measurement (an outdated practice from when bras lacked elastic), this calculator uses six specific measurements to provide a more accurate and nuanced starting point for finding a perfectly fitting bra. It is widely considered one of the most reliable methods available today, helping countless individuals escape the discomfort of poorly sized bras.

This calculator is for anyone who is frustrated with their current bras, experiences common fit issues like gaping cups or a riding-up band, or has never been professionally fitted. A common misunderstanding is that this calculator gives a definitive, final size. Instead, it provides a highly educated *starting point*. Breast shape, brand variations, and personal preference are all crucial factors that will influence your final perfect fit. Consider this the first, most important step on your journey to bra comfort.

abrathatfits calculator Formula and Explanation

The calculation is a multi-step process that prioritizes the underbust measurement for band size and the difference between bust and underbust for cup size. It uses an average of bust measurements to account for variations in breast shape and tissue distribution. The core formula is simple: Bust Circumference – Band Circumference = Cup Volume. However, the nuance is in how those values are derived.

1. Band Size Determination: The band size is typically derived from the snug underbust measurement. For comfort, especially for those with less “squish” around the ribcage, some formulas might average the snug and loose measurements. The result is often rounded to the nearest even number.
2. Bust Size Determination: To get a comprehensive measurement, the standing, leaning, and lying bust measurements are averaged. This accounts for how breast tissue behaves in different positions against gravity.
3. Cup Size Calculation: The calculator subtracts the *true* underbust measurement (not the final band size number) from the average bust measurement. The resulting difference in inches determines the cup size. Each inch of difference corresponds to one cup letter in the UK sizing system (1″=A, 2″=B, 3″=C, 4″=D, 5″=DD, 6″=E, 7″=F, etc.).

Input Variables for the abrathatfits calculator

Variable	Meaning	Unit (auto-inferred)	Typical Range
Loose Underbust	The circumference of the ribcage with the tape held loosely.	in/cm	24 – 50 in
Snug Underbust	The firm circumference of the ribcage, like a new bra band.	in/cm	23 – 48 in
Tight Underbust	The circumference of the ribcage on a full exhale, tape pulled tight.	in/cm	22 – 46 in
Standing Bust	Circumference over the fullest part of the bust while standing.	in/cm	28 – 65 in
Leaning Bust	Circumference over the fullest part while bent at 90 degrees.	in/cm	29 – 70 in
Lying Bust	Circumference over the fullest part while lying on your back.	in/cm	28 – 68 in

Practical Examples

Example 1: Common Mid-Range Size

• Inputs (inches):
  • Loose Underbust: 31
  • Snug Underbust: 30
  • Tight Underbust: 29
  • Standing Bust: 37
  • Leaning Bust: 39
  • Lying Bust: 38
• Calculation:
  • Band is based on the snug 30, so the band size is 30.
  • Bust average is (37 + 39 + 38) / 3 = 38 inches.
  • Difference is 38 (bust) – 30 (band) = 8 inches.
• Result: An 8-inch difference corresponds to a UK G cup. The starting size is 30G UK.

Example 2: Smaller Band, Larger Cup

• Inputs (inches):
  • Loose Underbust: 28
  • Snug Underbust: 27.5
  • Tight Underbust: 26
  • Standing Bust: 35
  • Leaning Bust: 37
  • Lying Bust: 36
• Calculation:
  • Band is based on snug 27.5, which rounds up to 28.
  • Bust average is (35 + 37 + 36) / 3 = 36 inches.
  • Difference is 36 (bust) – 28 (band) = 8 inches.
• Result: An 8-inch difference corresponds to a UK G cup. The starting size is 28G UK. Check out our sister size calculator for more options.

How to Use This abrathatfits calculator

1. Select Your Unit: Choose between ‘Inches (in)’ or ‘Centimeters (cm)’. The calculator will handle all conversions automatically. Inches are standard for this method.
2. Take Your Six Measurements: Use a soft measuring tape. For best results, measure without a bra on, or with a non-padded, unlined bra. Ensure the tape is parallel to the floor for all measurements.
3. Enter Your Measurements: Input each of the six numbers into the corresponding fields. The calculator will update in real-time.
4. Interpret Your Starting Size: The primary result is your recommended starting size in UK sizing. Note this down, along with the two sister sizes provided. A sister size down (e.g., 30G from 32FF) has a tighter band and one cup letter larger, while a sister size up has a looser band and one cup letter smaller. They have the same cup volume.
5. Start Shopping: Use this starting size to try on bras. Remember to check for a snug band, cups that fully contain your breast tissue without spilling or gaping, and a gore (center part) that sits flat against your sternum. Our bra fitting guide can help you diagnose fit issues.

Key Factors That Affect Bra Fit

Your calculator result is a fantastic starting point, but a true fit depends on more than just size. Breast *shape* is just as important as volume. Here are key factors to consider:

• Projection vs. Shallow: Projection refers to how far your breasts stick out from your chest. Shallow breasts have tissue spread more widely across the chest. A projected shape needs bras with deep cups, while a shallow shape needs wider, more open cups.
• Root Width: This is how wide the base of your breast tissue is on your chest wall. A bra’s underwires should follow this root perfectly. Wires that are too narrow will dig into breast tissue, and wires that are too wide may poke your armpits.
• Root Height: This describes how high up on your chest your breast tissue goes. It affects whether you need a cup that is open on top (for tall roots) or more closed (for short roots).
• Fullness Distribution: Are your breasts fuller on the top, bottom, or evenly distributed? This determines what style of cup will fit best (e.g., a balconette for bottom-fullness, a full-cup for top-fullness). Explore different styles in our bra style guide.
• Tissue Density: Firm, dense tissue will hold its own shape, while softer tissue is more malleable and will more easily fill out a bra cup.
• Breast Separation: The space between your breasts determines how wide the center gore of the bra should be. Closely set breasts need a very low, narrow gore, while wide-set breasts need a wider gore.

Frequently Asked Questions (FAQ)

1. Is the abrathatfits calculator 100% accurate?

No calculator can be 100% accurate because breast shape and brand sizing vary so much. It provides a highly accurate *starting size* which is a much better baseline than traditional +4 methods. You should always use this size as a guide to start trying on bras.

2. Why does this calculator give me such a large cup size / small band size?

This is a very common reaction! Mainstream stores have historically fitted women into a very narrow range of sizes, often putting them in a band that is too large and a cup that is too small. A correctly fitted band should be snug and provide 80% of the support. A cup that seems “large” by letter is simply one that correctly matches your proportions. Trust the measurements and try the size on—you might be surprised!

3. What is the difference between UK and US sizing?

UK and US sizing are the same up to a D cup. After that, they diverge. The UK system uses double letters (DD, E, F, FF, G, GG, H…) consistently. The US system is less standardized, often going D, DD, DDD, G, H… This calculator uses the more consistent UK system, which is used by many popular full-bust brands like Panache, Freya, and Curvy Kate.

4. What is a sister size?

Sister sizes are sizes that have the same cup volume but different band and cup letter combinations. To find a sister size, if you go up in the band, you must go down in the cup letter, and vice versa. For example, a 32F has the same cup volume as a 34E and a 30FF. This is useful if a bra’s band feels too tight or too loose but the cup volume is correct.

5. Why do I need six measurements?

The three underbust measurements help determine how much compression your ribcage can comfortably take for a snug, supportive band. The three bust measurements (standing, leaning, lying) create an average that accounts for breast shape and tissue distribution in different positions, giving a much more accurate volume estimate than a single measurement. Our guide to measure bra size has more details.

6. What if my measurements are between whole numbers?

This calculator accepts decimal points. Be as precise as possible, entering fractions as decimals (e.g., 30 1/2 inches should be entered as 30.5).

7. The calculator gave me a result, but it doesn’t feel right. What now?

First, double-check your measurements. Second, make sure you are performing the “scoop and swoop” method to get all your breast tissue into the cups. If it still feels wrong, refer to the “Key Factors That Affect Bra Fit” section and our guide to common fit problems. You may need a different style of bra for your breast shape.

8. Should I use inches or centimeters?

While the calculator works with both, the original A Bra That Fits method and the UK sizing system it’s based on are built around inches. For the most standard results, using inches is recommended.

Related Tools and Internal Resources

Deepen your knowledge and find the perfect fit with our other guides and tools.

• Bra Shape Guide: An in-depth look at projection, root width, and other crucial shape characteristics.
• Sister Size Chart: Quickly find alternative sizes when your recommended size doesn’t fit quite right in the band.
• Scoop and Swoop Tutorial: Learn the essential technique to ensure you are wearing your bra correctly.
• Bra Style Guide: Discover which bra styles (balconette, plunge, full-cup) work best for your shape.
• Common Fit Problems: A troubleshooting guide for issues like gaping cups, digging wires, and more.
• Bra Care Tips: Extend the life of your well-fitting bras with our expert care advice.