Originally Posted by sacafotos
One thing to keep in mind with sizing advice is that—this is my personal observation and opinion—the larger the foot, the less accurate the advice might be for you.
If I wear a size 7 UK and someone with size 12 feet gives me advice, even if his foot is shaped the same as mine, the advice might not work for me.
I feel it's because of a general issue with scaling that makers like G&G have brought up: proportions scale differently as the shoe size goes up. Eg., the heel of a size 7 might not be too far off from a size 12, but the length and width might be vastly different relatively speaking.
So for the most accurate sizing advice possible...try to find someone with similar shape AND similarly sized feet. I know that sounds obvious but I don't think many people consider this.
You are completely right that it is tough for advice from larger feet to work for people with smaller feet. We can deal with a larger variation in sizing because of the increased size of our feet. Sizes are based off of a standard increase in length and width per unit size, but as the foot is larger, the proportion of increase in size becomes smaller. A 1/4 inch increase in length for a size 7 is a much larger increase in size compared to the total length of the foot vs that same 1/4 inch increase to a size 13 shoe.
As a guy with very large feet, I can try on a half or sometimes even a whole size different in length and the fit can feel the same as long as the width size is adjusted to make the measured width the same in actual inches/cm/etc. i.e.: a size 10E vs a 10.5D vs an 11C are all the same in measured width even though the overall length of the shoe is different as well as the heel to ball measurement. For someone of average size they may be able to go from the 10E to the 10.5D and feel that they are fine with either, but slightly prefer one over the other.
In an extreme example of this, like myself, here is how it can work differently and actually make it more forgiving for large sizes to be slightly off in sizing. In Allen Edmonds on the 7-97 last, I can wear a 14A and a 15AAA. They both feel the same to me when wearing them, even though my actual length should be the 14 when looking at where my ball of my foot sits in the shoe. But since that relatively small increase is so minimal compared to the length of my foot, I really don't feel a difference at all. It also makes fitting different when there are usually not half sizes in most brands above a size 12.
This is all just for length and width of the shoe, where there are actually different sizes. It doesn't even go into the variance in proportion of the heel, toe box, etc. when increasing size.
So it is fine to use the general sizing advice that is given on SF, but you need to always take it with a grain of salt if you are a very small or large size. It is best to ask the professionals or at least look for guys of a similar size. if you are a smaller size, this will be very important because your level of tolerance between sizes most likely will be much smaller than you think. If you are a large size, you should be okay to be able to wear the pair without really noticing to much, even if you are a half size off.