Bra Measurement Calculation Difference: HerRoom Versus ABraThatFits

[MychalBloodwing]

I'm confused as to how there's such a big difference between the resulting bra sizes using my measurements. According to HerRoom (Lingerie Tips for Men - HerRoom) I'm a flat-chested 44AA. However, according to A Bra That Fits (https://www.abrathatfits.org/calculator.php) I'm a healthy 40C/D. What's the reasoning for Her Room adding 4 to 5 inches to an underbust measurement? Just eyeballing my chest, I know that I'm not flat chested.

[Newby]

MychalBloodwig, I am not sure why HerRoom adds 4-5 inches to the underbust measurement. 
 
When I used these two different methods for myself I was getting similar results as you.   I finally settled on trying a 40B t-shirt bra and that fits me very well.  I also fill the cups on a 40C underwire minimizer bra.  

Not all bras are the same, so you’ll have to find what works best for you. 

Good luck.

[gmast]

   Different manufacturers use different methods to determine sizes.  Supposedly, Bra sizing used to be based on blouse sizing.  Typically, bra sizes are based off the band size, and then the cup size is the difference between the bust measurement and the band size.  One some occasions I've seen them list it has band measurement instead of band size, but based on the accompanying calculator, that is an error due to incompetence
    There are several different methods of coming up with the band size.  Traditionally, it was underbust measurement +5 for the band size.  However bra sizing is not standard.  Many manufacturers have multiple sizing recommendations depending on if you used their charts or their calculators.  The manufacturers even size different models differently.  Here are several bra companies' and retailers recommended sizing methods for band size that I've come across.

Fruit of the loom:   Underbust measurement + 5 gives band size.
Champion Sports: Underbust measurement +5, round up to even
New Balance:        Underbust measurement +5, round down to even.
herroom:                Underbust measurement +5 if odd, +4 if even.
Wacoalbras.com    Underbust measurement +5 if odd, +4 if even.
Wacoal calculator: Underbust measurement  +4 if even, +3 if odd.
Brooksrunning       Underbust measurement +4, round up.
Warners:                Underbust measurement +4, round up.
Warners:                Underbust measurement +2, round up.
Anita - size charts:  Underbust + 3.6, round up.
Anita Calculator:     Underbust + 2, round up.
Warners:                Underbust measurement +1, round up.
Kohls, Bare Necessities, Justmysize:   Underbust, round up.
TrueandCompany:  Underbust, round down.

   And then some use the measurement above the bust for the band size.

Glamorize, Maidenform, Bali, Playtex, Herroom (alternate), Wacoal (optional):           Torso
Victorias Secret:                Torso, round down.

So depending on the method, chosen, it could be underbust to underbust +6 for a band size.  This is why is highly recommend you do not use abrathatfits or the retailer.  A better starting point is the manufactures recommendation.

Bottom line, you do not have a bra size, and anyone that acts like there is one, is a fool.  You have a bra size for a specific model of bra.

[Traveler]

Very through gmast. Probably why 80% of bra wearers have the wrong size. I haven’t used the herroom calculator but I have used the brathatfits calculator. It’s been pretty close with band size for me but the cup size has been way off. Even though they have an Assigned male at birth option, it’s still been too big on the cups by at least four sizes for me. Another reason a fitting is the gold standard.

[bikerbob]

Another issue I have run across that I don't see mentioned here is that a size that fits in an underwire may not work in a non wired bra.  Like many of you here, my breasts are widely spaced and I have nearly as much boob under my arms as on my chest.  When I stuff everything into an underwire bra, I nearly fill the cups on a 42C but don't even come close on a 42B non wired.  My wife can wear a 42C wired and non wired interchangeably but I can't because man boobs and girl boobs are different.  We have approximately the same volume but it is distributed differently.  Therefore sizing charts that work for women may not work for men which may account for some of the problems mentioned above.  I figured out what sizes work by trial and error.