This instructable will help you decide if that pair of pants will fit without ever having to try them on.
For most(I say "most' because I know this isn't a "one size fits all" universe and we come in many, truly beautiful, individual shapes) ladies, these ratios are practically infallible. If they don't work exactly for you, they will, at least, give you a better idea if the pants will fit and help in your decision to purchase or not.
***Please let me know if you try them and they don't work at all***
Step 1: Not a Waisted Effort
Take the pants off the hangar. Button them and then hold the waistband's side seams in each hand and drape them around your neck, like you're putting on a necklace. Or, you could put the pants around your neck like your putting on a cape (with the side seams coming together in the front).
You can gauge if the pants will fit your waist by seeing how much the pants overlap.
If you have to choke yourself, at all, to get the side seams to touch, just put those lovely pants back on the shelf, unless you intend to sell them on ebay or to your local upscale consignment shop. If that's the case, don't read on, just check for stains and tears and go about your merry way.
If waistband come together and you have breathing room (overlapping only an inch or so), Congrats! The waist is your size. Move on to step Two: Hip, Hip Hooray!
If the waistband overlaps more than an inch or two, the waist is too big for you. You'll have to now decide whether the pants are enough of a goldmine to do the alterations necessary for a proper fit. This is a strike against them.
Needless to say, this trick also works if you're looking at a skirt.
There's a bit of a rub, though, when you're looking at ultra-low waisted pants. With these, you have to account for the fact that the "waistband" doesn't actually hit you at (or sometimes, even near) your waist; it'll end lower (far lower). As such, you will need more overlap around your neck to compensate.
Step 2: Hip Hip Hooray
Are your shoulders wider apart? Then the pants will likely be too small over your hips. Back on the rack or off to eBay.
Are the pants just slightly wider than your shoulder span? Then the pants will fit your hips. Move on to "Rising to the Occasion"
Are the pant much wider than your shoulders? Then the pants are going to be roomy in the hip area. Strike Two.
Step 3: Rising to the Occasion, at Length
Find the place in the crotch of the pants where the seams come together. Take that spot, hold it up to your own crotch and check the lengths.
Check where the pants hit your waist (or hip, in the case of ultra low-rise pants). Is it where you want? Too high, or too low, or in the ballpark? Super!
Next, check the leg length. Did you want pants that are mid-calf, ankle-length or long enough to wear 4 inch heels? Are they that long? Great!
Step 4: Happy Hunting!
So, there you have it, some tricks to finding a great fitting pair of pants without trying them on.
They will also come in handy when there is a dressing room available, but you've only got a limited amount of time (not enough to take off your jacket, your shoes, your pants, then put on the pants in question, blah blah blah....)
I highly recommend that you try these hints first with pants you already own. Check how your favorite pair of jeans work and familiarize yourself with what dimensions they are (maybe you like a looser fit in the waist, so more than "just an inch" would suit you better).