This question is rather complicated since your laptop's power consumption fluctuates a lot depending on if you're gaming or simply browsing the Internet on the laptop. This affects the time and percentage Omnicharge can charge your laptop.
So to simplify the question, we use a more objective method by comparing Omnicharge's battery capacity to the laptop's internal battery capacity. Also considering the efficiency loss of Omnicharge's conversion circuits, the equation of charge percentage is:
Omnicharge's battery capacity / laptop's internal battery capacity * Omnicharge's conversion circuits efficiency
Take the Omni 20c+ and 15'' MacBook Pro (2019 model) for example, the Omni 20c has a 71Wh capacity; the 15'' MBP has an 83.6Wh internal battery; the Omnicharges conversion efficiency is around 90%. Put these numbers in the above equation and we get:
71Wh / 83.6Wh * 90% = 0.76
This means that the Omnicharge can charge the 15'' MBP around 76%. This is assuming that the laptop is turned off or in sleep mode. Operating the laptop while charging will impact this calculation.