Seven days, ten days, two weeks. Which one suits your trip? Here's what you can realistically cover without spending half your holiday in a car.
A week is tight. You can do Colombo, Kandy, the Cultural Triangle, and one beach town — that's it. You'll skip the hill country entirely unless you fly into Colombo and out via a different route, which adds cost. Seven days works best for a focused trip: two nights in Kandy/Sigiriya, two nights in Galle or Mirissa for the coast, one night near the airport. You'll wish you had more time, but you won't feel like all you did was drive.
Ten days is the sweet spot. Add the hill country — Kandy to Nuwara Eliya to Ella — and keep one coast stop. That gives you a proper cultural triangle visit, the train ride, two or three days on the beach, and no single drive over five hours. Most first-timers land on this length and it works.
Two weeks lets you do the full circuit: cultural triangle, hill country, south coast, and a side trip to Yala or Udawalawe. You could even split the coast and do Galle for a few days plus one east coast stop if you're traveling in the right season. Two weeks gives you breathing room — you can spend three nights in places instead of one, which makes a massive difference to how the trip feels.
Anything over two weeks gets you into slow travel territory: fewer moves, deeper dives, maybe a volunteer stint or a weeklong surf camp in Weligama. That's a different kind of trip, and it's where Sri Lanka really shines — when you stop rushing between dots on a map.