"Green tea. usually contains around 25 milligrams of caffeine per 8-ounce serving. It's about half of the amount of caffeine found in a typical cup of black tea and one-quarter of the amount found in a typical cup of coffee."
Depending on the brand, it's equivalent to a half of cup of coffee. Although green tea contains l-theanine which helps offset the jitters from caffeine. Personally I try to limit caffeine to the most bare minimum as I personally find that it causes a reduction in my emotional spectrum.
From: https://www.thespruceeats.com/caffeine-in-coffee-tea-cola-76...