Rule #1: you can't count on any two women's clothing or shoe sellers to have the same measurements for a specific size. Same goes for manufactureres. Payless Shoe Source. in the US has wonderful sizing charts. Each size has the measurements for width and length. You can exactly compare men's and women's size and width and match by measurement rather than size. You have to try on actual shoes from a specific manufacturer to be sure what fits. After that you can pretty much count on that manufacturer-size to use the same size lasts (shoe forms). Two useful web pages:
http://www.i18nguy.com/l10n/shoes.html
http://www.payless.com/en-US/Consumer/CustomerSupport/Finding_Size.htm#sizecharts
Rule #2 US Men's is approximately equal to UK Women's size, but opinions vary(because actual sizes vary). US women's is about two sizes larger than US men's for the same foot. A man with a size 10 wears a womans size 12. However, this varies again by manufacturer and I am able to wear Payless womens shoes only one size larger than my men's size...i can squeeze into the SAME size but not for long and its not good for my feet/toes. In a pinch (perhaps literally) you may be able to compensate for width by going up a length size; less likely, you may be able to compensate for length by going up a width size, but it doesn't work as well and in both cases the shoe distorts. I don't recommend it for shoes you wear out a lot walking.
Conversion tables for country and sex vary. See rule #1. Your feet may have variations that effect your shoe size. Your arch height, pronation or suppination of the foot while walking (look for where the wear is on the soles of your old shoes), etc can affect what size you can take beyond the length and width of your foot.
Rule #3: Your feet swell as the day goes on. Don't try on/measure for shoes until you have been up and moving around for some time or the shoes will be too small in the evening. Do some walking before trying on shoes...and I don't mean just from your car to the shop.
Rule #3A: You will ignore my advice and buy shoes in the morning that will fit tight in the evening. I did it myself last week. You will not be able to resist that pair of shoes. So ALWAYS shop for shoes late in the day.
rule #4: If you buy closed toes shoes, be prepared to buy larger sizes than open toe/sandles. If the shoe is narrower, and the average womens shoe is (a wide womens being equivalent to a normal width man's in many cases...that is women's D-wide may be equivalent to a man's normal width, for example. The higher the heel, the larger the shoe size you need in most cases. You might fit a 1" heel women's 12 but need a 13 for a 5" heel. Subtract any sole/platform height from the heel height for effective heel height (a 6" heel on a 2" platform shoe is only 4" of actual heel rise). A listing of Medium with for a male may mean a D while a woman's medium is a B. This is the reverse side of what I said above. There are many sites that will let your print out a shoe measuring chart like that little gadget they use in shoe stores made of stainless steel. You stand on the printout and measure your foot. Be careful to stay vertical with your marking implement. It's tricky, but better than guessing and you won't be far off. These sites have downloadable footsizing charts.
www.famousfootwear.com
www.italianheels.com
Rule #5: Find out about the seller's return policy. Do NOT mark up the sole's walking on gravel or rough surfaces or they will not take them back. Be nice, wear stockings while trying on new shoes until you decide to keep them.
Rule #6: Life is much easier if you shop in stores and actually try on the shoes and walk in them. I was a bit shocked recently while walking around a TG store in shoes I was thinking of buying....the owner said that I was the only TG that did that. Most just tried them on and stood in a small rear area of the shop. I'm sure that many don't even do THAT in a regular shoe store....I'm not ready to
One of my reasons for supporting the higher prices in TG stores is that they provide the opportunity to try on items in "safety"...they deserve to be paid for the extra cost for them in supplying a smaller client base. In addition, larger size shoes often cost more wholesale.
Rule #7: No matter how much you like the shoe...if it doesn't fit you will regret it. I recently went to buy a pair of shoes that I had wanted for about 2 yrs...when i tried them on the non-adjustable strap cut into the top of my foot....I bought a different style in the same metallic silver and a second pair with adjustable straps across the top of the foot. They felt wonderful and I forgot (almost) about the pair I had wanted. I have a pair of shoes I outgrew. I only wore them once since then. My feet hurt for two days. Now I wear them for a few minutes and don't walk in them. I am going to replace them with a larger pair of similar style.
Rule #8: Shop around. Many shoes come from a manufacturer who does not retail. Their shoes can end up on different sites, with different names or identification numbers at very very different prices. Since a Retailer may buy from different manufacturers, the canny girl will learn brand names of shoes and buy by the brand name, not the store or website, in order to get the same actual size in a shoe.
Rule #9: Learn to Google...Advanced Google...no, iI mean REALLY take the time to learn how to use at least one Search Engine really well. It will save you vast amounts of time in the long run. It will also let you comparison shop for an item. Many sites DO use the same manufacturer's ID/name for a shoe. Don't forget to learn what works well in the "without the words" box. On most searches for "at least one of the words: crossdresser, transvestite, transgender" I automatically put in "without the words: XXX, porn, pics, free" to avoid the sex sites. If I want to buy from a North American source I add "UK" to that box. This can really cut down on your # of hits and eliminate hours of wasted surfing time.
CUSTOM SHOES: Some places will make shoes to fit your foot. I have some listings for women's custom made shoes, but cannot find them right now. I will try to post them soon, if I can find the folder I put them in. Do not confuse custom-ASSEMBLED shoes with custom-fitted shoes. The first are just modular shoe parts, the second are made to fit YOU.
http://www.digitoe.com/short_stories/custom_fit.html
http://www.cigaraficionado.com/Cigar/CA_Archives/CA_Show_Article/0,2322,759,00.html (only for reference on how construction differs, these are men's shoes and they are very very very expensive)
http://www.herseycustomshoe.com/ (again, only for reference on how construction differs, these are men's shoes)
You do a tracing and they work with you to build a last of your foot. All shoes are custom built to your last. This is not cheap. However....it is the best way to buy any shoe, just as a bespoke suit is the best fit in a suit. The last only has to be done once unless your size changes.
Advantages are that shoes fit really well and are comfy to walk in. Even heels are easier to wear for long periods. You may be able to get shoes in colors that you can not normally get and match color, material and style to your requirements. Great for matching an outfit with just the right shoe. They often last forever and are stronger. You don't HAVE to go out in public trying on women's shoes to have a good fit.
Disadvantages are a smaller selection of shoe styles, higher costs (as with any superior product), you don't GET to go out in public trying on women's shoes to have fun.
I hope this helps. I would love to see some hints from girls who DO shop in actual stores for women's shoes, en femme and en homme. Do you get personal service? Take shoes home to try on or try them in the store? I found out I could buy a gift card at Payless and then use it to shop online and not have to use my credit card or bank account. With a mailbox service with a street address and a "second" (femme) name on the mailbox account (I have never had to bring in my "girlfriend" to sign a form in the mailbox business, just a signed card for the Postal Service) you can completely hide your purchases if your lifestyle demands it. Paying with a pre-filled PayPal account also hides your checking account/credit card info from the seller and your purchases nature from the bank and credit card company.
Unfortunately your PayPal account must match the name on your credit/debit card. I have not yet figured out if you can get a second card issued on your account with a debit card without having to bring the second person in to sign a bank signature card....I think not. A credit card company will do a credit check on the person you add on the second card. I have not figured out a legal way to manage a way around this, but I suspect that if you do, and pay the bills on time (mail a good check to the card company BEFORE you use it) nobody will ever find out and you will not have committed a criminal act...check the part where you sign stuff to see if it is.
There are some lovely shoes on that site, shame about the price though, but if they fit they should be worth it 
