Measurement for the amount of simulated noise

Hi all,

I have an analytical function, say h. I want to test my algorithm against noise by adding hbar = h + n, where n follows a normal distribution with zero mean i.e. n ~ N(0, \sigma).

Now, how do I make a meaningful measurement of noise from \sigma? Like I want to have a percentage/DB for a value of SNR, but I don't know how to calculate that...

Many thanks,