1. Always get a bra fitting
The number one rule of thumb (or breast) is to get a bra fitting every time you purchase a new bra. And seek out decent lingerie boutiques with trained fitters. Fitters have an uncanny ability to pick the size and style that will suit your body shape before they've even seen you in a bra. They've also got access to and knowledge of brands you may never have heard of so trust their advice. However, if you're not happy with the fit, ask to try another style. The process doesn't have to be daunting: if you don't like the way the bra feels on your body, don't buy the bra. Simple.
2. Try on every bra you see
ALWAYS try on bras - sports or not. Even if you already have the same style in a million other colours and have worn it since you were 15. (Especially if this is the case). Manufacturing 'quirks' can result in bras differing ever so slightly whether due to colour, stitching or fabric. For example, black bras tend to be a teeny bit smaller than their white counterparts as the dye can shrink the fabric.
3. Beware of size denial
Women can be MASTERS at denial. So, the next time you reach for the 12C when you're probably a D cup or above, think of the shoe example mentioned above: it helps to give some perspective on just how silly (and painful) it is to wear the wrong size. So, first, once you pop a bra on, scoop your breast into the cup with your hand and make sure your nipple is centre. Popping over the top? Too small. Floating around with room to move? Too big. Simple. Adjust accordingly. However, if things still aren't measuring up, consider this: cup sizes operate on a sliding scale which means they're not the same for all sizes. Give or take a few millimetres a:
12B fits the same as a 10C - the only difference is that it fits more snuggly and securely around your back so if you hover between sizes (and always need the elusive size "11" or "13" or "15") try your size equivalent. Need more examples?
A 12DD fits similarly to a 10E. It does NOT mean you've suddenly put on weight or have been deluded for years, it's simply a sliding scale.
Fit a 14C but not convinced? Try a 12D for a firmer fit or a 16B to loosen the fit.
16DD but not happy? Play around with a 16E or shift the band size too - try a 14E (the exact equivalent) and a 14F.
4. The bra band should fit firm and low on your back
Just because your bottom is a bootylicious size 14, it doesn't mean your back measures the same. The band should fit around the smallest part of your back - your rib cage - and often (especially if you're curvy) it's significantly smaller than your hips and bottom.
If the bra band rides up to your shoulder blades, it's too big. Try going down a size in band (eg 14 to a 12) and go up in cup size to compensate for this change (14D = 12DD). 90% of the support of the bra comes from the band so make sure it sits low and firm to hold everything up.
Research conducted by Berlei and the Australian Institute of Sport has revealed that during high-impact exercise an unsupported 12B bust can bounce up to 8cm, and a 16DD bust can bounce up to 19cm.
This movement can damage soft tissue and stretch delicate Coopers Ligaments, which can ultimately cause breasts to sag. So strap them in, ladies!
Most importantly: your bra must be firm on the loosest fitting so that once the bra stretches (and like a new shoe, it will), you are able to tighten it. That is, tight on the first hook with 2 or more hooks left to tighten further.
5. Make sure the underwire sits flush with your body
Underwire helps to support and shape your breasts (although there are great wire-free alternatives on the market). Underwire should surround and support your breast—not poke into it! Take a look - if it rests on the side your breast tissue, it's too small. It should also sit flat in the centre between your breasts. If the wire pulls away from the body in the center, then the cup size is too small. A good way to test this is to simply sit down in the change room. Notice any buckling? Does the centre of your bra poke away from your body? Yep! Too small.
6. The 'jump' test
It's pretty simple. Put on bra. Stand in front of change-room mirror. Jump. Jump up and down. Turn to the side. Repeat. Take note of what is happening to your breasts. If they're budging even in the slightest, try another bra.
7. The strap test
If your bra fits perfectly when the straps are on their tightest, it's time to let go and find another one or commit to getting the straps altered. Why? Because the bra is going to stretch and you need room to tighten them up over time so no room to move means a lack of support and bra straps sliding off your shoulders. Next!
8. Why shape matters
If nothing is working, change tack - it could be as simple as a matter of shape. It's not just how big or small your bust is or how wide or narrow your back, shape (and where you carry weight in your bust - to the side, in front etc) plays a big part too. So, if you're bulging over everything, try a deep, high cup (think Panache, Freya) or if you're not filling anything properly, go for a straighter, balconette style - think Triumph tri-action.