By ferry (scenic)
Ferries and speedboats run daily from Ao Nang, Railay's floating pier, or Krabi Town's Chaofa Pier to Phuket's Rassada Pier, taking roughly 2 hours on standard ferries or as little as 90 minutes on faster speedboats. Many routes call at Koh Phi Phi en route, which adds time but means the crossing doubles as a scenic detour past some of the region's best-known limestone scenery. Services depend on sea conditions and run less frequently outside the November-April high season.
By bus or minivan (cheapest)
Buses leave roughly hourly from Krabi's bus terminal, taking about 3 hours to cover the ~160km road route to Phuket's bus terminal. Shared minivans cover the same route, often with hotel pickup, though timing varies more depending on how many stops are made along the way.
Which to choose
If you get seasick or prefer certainty, the overland bus or minivan is the more reliable choice year-round. If you want the classic Andaman Sea views (and don't mind paying more), the ferry — especially one routing via Phi Phi — is the better experience.
By private taxi
A private car covers the same overland route in 2-3.5 hours depending on traffic, with no waiting for a shared van to fill up — the fastest land option, at a proportionally higher cost.
Why there's no direct flight
Both Krabi and Phuket have their own international airports, but there's no direct flight between them — any air connection routes via Bangkok and takes considerably longer than simply driving or taking the ferry.