Guide to Measuring Bra Size Using A Bra That Fits

Finding the right bra size can make a huge difference in comfort, support, and confidence. The A Bra That Fits (ABTF) community, particularly known from its popular Reddit forum (r/ABraThatFits), has developed a reliable, straightforward method for measuring bra size that accounts for individual body shapes and breast characteristics. This guide will walk you through the ABTF method in a clear, step-by-step manner, ensuring you can measure yourself accurately at home. It’s designed to be easy to understand, even if you’ve never measured for a bra before. 

You can access the ABraThatFits (ABTF) online calculator HERE. 

Why Use the A Bra That Fits Method?

Traditional bra sizing methods often rely on outdated techniques, like adding inches to your underbust measurement, which can lead to ill-fitting bras. The ABTF method uses precise measurements to determine both band and cup size, accounting for the diversity in breast shapes and sizes. This method is widely respected because it’s based on real-world feedback from thousands of people and prioritizes comfort and fit over arbitrary standards.

To follow this guide, you’ll need a soft measuring tape (the kind used for sewing), a mirror (optional), and a comfortable, non-padded bra or no bra at all. If you don’t have a measuring tape, you can use a piece of string and a ruler. The process involves taking six measurements to calculate your band size and cup size accurately.

Step 1: Gather Your Tools and Prepare

Before you begin, ensure you’re in a comfortable, private space. Wear a non-padded bra that doesn’t significantly alter your breast shape, or measure without a bra for the most accurate results. Stand up straight with your arms relaxed at your sides. If possible, have a mirror to check that the measuring tape is level around your body. The tape should be snug but not tight—think of it as a solid hug, not a squeeze.

Step 2: Take the Six Measurements

The ABTF method relies on six key measurements: three for the band and three for the bust. These measurements help determine your size and account for variations in breast shape. Use a soft measuring tape and measure in inches (or convert from centimeters later, if needed). Write down each measurement to the nearest 0.1 inch for precision.

Band Measurements

    #1 Snug Underbust

    Wrap the measuring tape around your ribcage, just below your breasts where the bra band would sit. Pull the tape snugly, ensuring it’s level all the way around. Exhale gently to get a natural measurement, as you don’t want it too loose or too tight. Record this number (e.g., 30.5 inches).

    #2 Tight Underbust

    Measure in the same spot, but pull the tape as tight as you comfortably can without causing pain. This mimics the firmness of a bra band. Record this number (e.g., 29.0 inches).

    #3 Standing Underbust

    Measure in the same place as the snug underbust, but with the tape slightly looser, just touching your skin without pulling. This is less commonly used but helps confirm your band size. Record this number (e.g., 31.0 inches).

    Bust Measurements

    #4 Standing Bust

    Measure around the fullest part of your breasts while standing upright. Keep the tape level and snug, but not compressing your breasts. This is usually around the nipple area, but it varies depending on your breast shape. Record this number (e.g., 36.0 inches).

    #5 Leaning Bust

    Bend forward at the hips so your torso is parallel to the ground (a 90-degree angle). Measure around the fullest part of your breasts in this position. This measurement captures the volume of your breasts, especially if they are pendulous or less firm. Record this number (e.g., 38.0 inches).

    #6 Lying Bust

    Lie down flat on your back and measure around the fullest part of your breasts. This helps account for how your breasts settle in different positions and is particularly useful for softer or less projected breasts. Record this number (e.g., 37.0 inches).

    Step 2.5: Enter your measurements in the ABTF calculator and see your result. 

    You can just enter the six measurements into the online calculator now if you want easy street. Select what sizing system you want (ex. US or UK), and a few other optional details. Then get your bra size! 

    Keep reading if you want more info on calculating band and cup size, though.

    Step 3: Calculate Your Band Size

    Your band size is determined primarily by your snug underbust measurement. In the ABTF method, you don’t add extra inches like in older sizing methods. Instead, round your snug underbust measurement to the nearest even number, as most bra bands come in even sizes (e.g., 30, 32, 34).

    If your snug underbust is 30.5 inches, round to 30 or 32. Use your tight underbust to decide: if it’s close to or below 30 (e.g., 29.0 inches), go with 30. If it’s significantly lower, you might try a 28 if available, as some brands offer smaller bands.

    If your snug underbust is between two even numbers (e.g., 31.5 inches), try both the lower and higher band sizes (30 and 32) when testing bras, as band stretch varies by brand.

    For example, a snug underbust of 30.5 inches and a tight underbust of 29.0 inches typically suggests a band size of 30.

    Step 4: Calculate Your Cup Size

    Cup size is determined by the difference between your band size and your bust measurements. The ABTF method uses all three bust measurements (standing, leaning, and lying) to account for breast shape and volume, then averages them for accuracy.

    Calculate the Differences

    Subtract your snug underbust from each bust measurement:

    • Standing bust (36.0) – Snug underbust (30.5) = 5.5 inches
    • Leaning bust (38.0) – Snug underbust (30.5) = 7.5 inches
    • Lying bust (37.0) – Snug underbust (30.5) = 6.5 inches
    • Average these differences: (5.5 + 7.5 + 6.5) / 3 = 6.5 inches.

    Determine the Cup Size

    Use the average difference to find your cup size. In the ABTF method, each inch represents one cup size starting with A :

    • 1 inch = A cup
    • 2 inches = B cup
    • 3 inches = C cup
    • 4 inches = D cup
    • 5 inches = DD/E cup
    • 6 inches = DDD/F cup
    • 7 inches = G cup
    • And so on (continues with H, I, J, etc., depending on the sizing system).

    If you’re between a sizes (ex. 6.5 inches), start with the smaller cup, but try the larger cup if the smaller feels too small.

    Step 5: Consider Breast Shape

    Bra size is just the starting point. Consider these factors and read this blog post for more info:

    Projection: Are your breasts more forward-projecting or shallow? The leaning bust measurement being much larger than the standing bust (e.g., 40 vs. 36) suggests more projection, so you may need bras designed for projected breasts.

    Root Width: Do your breasts start close to your shoulders or farther down? This affects whether you need narrow or wide underwires.

    Fullness: Are your breasts fuller on top, bottom, or evenly distributed? Is most of the volume on the outside (outer full) or on the inside (center full). This impacts whether you need full-on-top, full-on-bottom or other bra styles.

    You can assess shape by looking in a mirror. Trust your gut on this. 

    Step 6: Try On Bras and Adjust

    Once you have your calculated size (e.g., 30F), try bras in that size and sister sizes (e.g., 32E or 28G) to account for brand variations. Sister sizes maintain the same cup volume but adjust the band size (e.g., 32E has the same cup volume as 30F but a looser band). You can read more in-depth about sister size in this blog post. 

    Check for these signs of a good fit:

    • The band is snug and stays in place without riding up.
    • The cups fully contain your breasts without gaping or spilling over.
    • The underwires sit flat against your ribcage, following your breast root.
    • The straps stay in place without digging in or slipping.

    If the fit isn’t perfect, try different styles or brands. UK brands like Panache or Freya often align well with ABTF sizing, while US brands may use different cup progressions.

    Step 7: Use Online Resources

    The A Bra That Fits community (r/ABraThatFits on Reddit or their website) provide brand recommendations, fit checklists, and forums to ask for advice. If you’re unsure about your measurements or shape, their community can help troubleshoot.

    Then come back here to buy or request that bra! 

    Final Tips

    Measure Regularly

    Your size can change due to weight fluctuations, hormonal shifts, or pregnancy. Re-measure every 6–12 months or if your bras stop fitting well.

    Be Patient

    Finding the perfect bra may take trial and error, especially if your size is outside common ranges (e.g., 28G or 40A).

    Use Us to Find Specialty Brands, Sizes and Styles

    We can stock bras in just about any brand, style and size. So get in touch if we don't already have it! 

     

     

    Reach out to us if we can help further or offer recommendations. Happy measuring!