Using confidence intervals to determine winrate with low sample size?

[BIG NIGE]

Does anyone know what the formula is for determining the minimum expected winrate for a specific level of confidence (eg, 90% or 95%), given a sample size and actual winrate? I learned this in statistics class a few years ago but have since forgotten it. Do I need to know the standard deviation? For example, suppose I have a sample size of 8, and an actual winrate of 135.2% ROI. With 90% confidence, what is my minimum expected winrate? This is for one-table, 9-player $22 SNGs on Pokerstars, so if SD is necessary to know then just use a typical one. Thanks to anyone who can help.