Corset size

I know corsets need to fit snug how do i know the size if it fits too tight or to loose? I have a N/A waist, but for a corset, would I normally order something 4" smaller than my waist size? What is the length for the corests?

Solution:
Corsets are tailored as net body size, no extra space, moreover, each corset leave flexible spaces by lacing up part, can be tied tightly close to body.
a. For standard sizes corsets in the chart:
http://store01.prostores.com/fanplus...andardsize.jpg
It tailored for average person 5 feet 5 inch (165cm) high.
And the bust/waist/hip is tailor as net size, that is, for example, the finial corset of US 10 would be tailored a bust and waist circumference at 34in,26 in, in the condition of the lacing up part totally loose.
b. Custom size corsets.
Beside the standard size choice, corsets can be custom made too, same as all other apparels of us. Custom size corset can be made according client's height, net bust, net underbust circumference, nature waist, hip, and other requirements on length, color, fabrics or wearing habit (for example,' the corset may be worn with thick blouses, leave extra 1 in on waist/bust for the inside blouse').
Custom making is a free service, no extra cost, unless there is special requirement on remaking pattern, change fabrics, etc.