As you might imagine, Starfield will need hundreds of hours for people who really want to do everything, and Bethesda has already said the upcoming game is bigger than anything they've ever done before.
But if you solely focus on the main campaign, how long is Starfield? This has now been revealed by director Todd Howard in an interview with IGN:
"This one's ending up a little bit longer [than our previous games] and we may tune that some still. It's more quests, so it might be 20% more than our previous ones."
Howard when on and clarified this means it "might be in the 30s, maybe 40". Howard also says they will continue to flesh out the game after the release for quite some time, and he has high expectations on the modding community, which tends to do great things with Bethesda's titles:
"We've learned that people do play our games for a really, really long time. They're still playing Skyrim - not straight for 10 years, but they leave it and they come back and there's extra content. Certainly we're going to be doing extra content for this game, and we love our modding community. We actually think this game, for our modding community, is going to be a dream as there's so much they could do."