What Comp said.
Here is a rough estimate:
24 mg of nic is roughly equal to full flavor cigarettes like Marlboro Reds.
12 mg nic = Marlboro Lights
6 mg nic = Ultra lights
Keep in mind that these are just guidelines and are not exact, but it will give you a ballpark to start in.
I was a pack a day Marlboro Light smoker but I started with 24 mg of nic until I got off the analogs for several months. Then, I dropped it down to 12 mg for daily use. Now, I'm all over the place. When I can't vape very often I go to 24 mg so I can take a few draws and I'm good for a bit. During a "normal" day, my go-to is 12 mg. At night when I'm chain vaping to my heart's content I'm now dropping it down to 6 mg so I don't get too much nic. YMMV.