just looking at the exposure of your lungs to smoke..
1 bowl of shisha = approx. 1+ hour
1 pack of (20) cigarettes = approx. 1.5 hours (if you smoke a cigarette between 4-5 mins)
so by looking at the duration that your lungs are exposed to smoke both should be around the same.
the more accurate way is probably looking at weight of tobacco you smoke (grams of tobacco in a pack/grams of tobacco in a bowl)
Smoking Hookah is More Harmful Than Cigarette
"hookah smokers inhale more often and for longer periods than typical cigarette smokers"
Published by Harvard Mental Health Letter
Hookah Smoking as Tough on Lungs as Cigarettes
"Study finds one-hour session produces as much carbon monoxide as a pack of smokes"
- the study only looked at CO, but it shows its really not that much better
Pipes and Hookahs Pose Same Risk as Cigars
Smoking hookah/cigarettes is bad for your health period but, we all made this choice to smoke so we just gotta deal with it.