The ideal amount of lumens for a porch light ranges between 200-400 lumens in our experience.
If you choose to put a light directly on your porch, you'll want to have about 400 lumens to help clearly see the door as you're trying to enter. If you're looking for something less bright looking, you can go for a light that's closer to 200 lumens.
To get the best estimate for your porch, you can check out our guide on lux vs lumens to further understand the terminology behind light sciences.