It depends on a lot of factors, such as your body weight and tolerance. In university a 10mg edible would put me on a nice high for hours. Nowadays I'd need to consume at least 40mg to even feel it. To answer your question though 40mg is a large dose, especially for someone who hasn't used cannabis with frequency. I recommend most people start out with 5-10mg.
What I find really fascinating is that the route of administration can affect your tolerance even if the potency theoretically should be the same. If you consume edibles often (eg for health reasons) you'll find you increasingly need larger and larger doses until it plateaus somewhere. If you "switch it up" and consume the same quantity via, say, a concentrate you vaporize, it'll hit you a lot harder. Even if you don't change the route of administration but the circumstances (like a new location) there's a similar effect.
What I find really fascinating is that the route of administration can affect your tolerance even if the potency theoretically should be the same. If you consume edibles often (eg for health reasons) you'll find you increasingly need larger and larger doses until it plateaus somewhere. If you "switch it up" and consume the same quantity via, say, a concentrate you vaporize, it'll hit you a lot harder. Even if you don't change the route of administration but the circumstances (like a new location) there's a similar effect.