Use this simple z score calculator to calculate both positive and negative z scores
ZScore Calculator
Population Mean: 
The mean (average value) of the population to which the unstandardized value belongs. 

Population Standard Deviation: 
The standard deviation of the population to which the unstandardized value belongs. 

Value: 
The unstandardized raw value for which you want to compute a Zscore. 

ZScore: 
You can also find here a Z Score Table.