How do you find a bra that fits? Simple question. But today, the answer is more complex than you might think.

I started off writing this to find out a) whether the “4-inch rule” many of us learned from our moms (or, honestly, from Oprah) is still the best way to find your supportive soul mate. (Quick tutorial if you’re not familiar: You measure around your ribs, add 4, and voila you have your ideal band size.) Or b) if the 4-inch rule isn’t the thing anymore, what is?

The answer, just like on the SATs, is “c.” And here it is.

“Every lingerie company has different bra patterns so [the 4-inch] trick doesn’t work for all.” —Stephania Stefanakou co-founder and CEO of House of Anesi

A deep dive into the inner-workings of the intimates-biz quickly revealed that, just like you might wear a size 8 at one shoe store, and a 7 at another, cup and band parameters no longer operate according to an industry-wide standard.

After many a conversation in the Well+Good office about bra sizing, though, we came to one conclusion: in practice, it’s not always that simple.

“Every lingerie company has different bra patterns so [the 4-inch] trick doesn’t work for all,” explains Stephania Stefanakou co-founder and CEO of lingerie brand House of Anesi. Now, buying a bra without slipping straps, a suffocating band, or overflow-inducing cups requires Nancy Drew-style detective work, whether you buy online or head to your neighborhood Victoria’s Secret.

Below, you’ll find all the info you need to locate your comfiest bra yet, according to modern day lingerie experts.

If you’re shopping online…

Kick off your perfect fit quest with the understanding that the bra size you’re wearing now likely won’t be the ideal one to add to your cart. “We initially looked into different measuring algorithms but discovered that they weren’t always accurate due to every woman’s body being unique,” says Michelle Cordeiro Grant, founder and CEO of Lively. Without a golden standard to turn to, online retailers have had to curate their own rules in the form of size guides, online quizzes (like ThirdLove’s), phone calls, and even Skype consultation (yes, seriously).

Still, the new order relies a lot on trial-and-error. “Our method is to have women order the size that is closest to what they feel works while also encouraging them to try out sister sizes, which is why we offer free shipping and returns,” explains Grant. Le Mystere follows the same protocol, allowing returns and exchanges so long as the tags are attached and the fabric is unworn. Companies like ThirdLove take the process one step farther, permitting you to try your bra for 30 days (before paying, I might add).

All this adds up to one, unequivocal fact: If you’re so not in favor of frequent trips to your local post office, hunkering down to follow the nitty-gritty sizing instructions on each website is essential.

All this adds up to one, unequivocal fact: If you’re so not in favor of frequent trips to your local post office, hunkering down to follow the nitty-gritty sizing instructions on each website is essential. Some will tell you to go by the measurement you reach by cinching the measuring tape right around your ribs, and others will offer different instructions. So make sure you read up before entering your credit card info.

If you’re shopping in-store…

If try-before-you-buy is your preferred bra-purchasing method, you’ll most likely be in the hands of a fit specialist (phew). Even if you are receiving expert help though, there are a few ways to double—and triple—check that you’ll be walking out of the store with utmost support. Here’s a quick checklist to run through before calling the intimate yours:

1. Make sure you can fit only one or two fingers under the band.According to Le Mystere’s fit guide, you should only be able to slide a finger or two under your band at all times. If you have too much or too little space, a size up might work better for you.

2. While you’re in that same area, make sure the band moves horizontally across your back.If the band makes more of a rolling hill shape across your upper back than a straight line, your straps or your band size might be to blame.

3. Feel your underwire suffocating the bottom of your boob? You shouldn’t.If you kind of feel like your bra-to-be (or not-to-be, in this case) is a breast noose, ThirdLove posits that you likely need a snugger band to keep the wire from shimmying up your rib cage.

4. Check to make sure your straps aren’t digging into your shoulders.Your shoulders should never feel like they’re bearing the weight of your boobs. That’s really the band’s job, according to the guide. So if you do find that standing up straight gives you hunchback posture, opt for a smaller band size instead.

5. Make sure your cups aren’t encouraging gaping or overflow.If there’s space between the top of your breast and the cup, you either need to tighten your straps or size up. If the reverse is true, and your experiencing some spillage either on the sides or over the top of the bra, going up a size will do the trick.

Now that bras are taken care of, let’s talk undies. These pairs are (yesss) wedgie-proof and this bar of soap is the best intimate-washer out there.