Batting strike rate is calculated as (No. of runs / No. of balls faced) * 100.
How is bowling strike rate calculated?
Bowling strike rate is a measure of how frequently a bowler achieves the primary goal of bowling, namely taking wickets (i.e. getting batsmen out).
Bowling strike rate is defined for a bowler as the average number of balls bowled per wicket taken.
According to this page:
A bowlers strike rate is calculated by dividing the number of balls he or she has bowled by the number of wickets taken with those balls.
For example if a bowler has bowled 2000 balls in his career and has taken 50 wickets, he has a bowling strike rate of 40.00. In other words the bowler has taken, on average, a wicket every 40 balls.