To get from Langkawi to Penang, you have a number of travel options available, so depending on your budget, you can choose to:
1) Take a direct ferry from Langkawi to Georgetown on Penang Island.
2) Take a direct flight from LGK to PEN.
3) Take a much shorter ferry to the mainland, then continue your journey by either bus or train to Butterworth. This works out around half the price than taking the direct ferry, so if you want to save money and don't mind the longer trip, this is the best way to go.
The direct ferry leaves Kuah jetty just twice a day and usually takes two and half to three hours to make the trip to Penang Island.
If you are travelling on a budget and don't mind a much longer journey, you can get to Penang for half the price of the direct ferry if you take the following route.
This journey involves taking the much shorter ferry ride to the mainland, to Kuala Kedah Jetty.
Once you arrive at K. Kedah, you can then take a local bus to Alor Setar city centre from the main road in front of the ferry terminal (or taxi for about 20 RM if you want to get there quickly or there are a few of you to share the cost).
Ask the bus driver to let you off at the nearest stop to the Alor Setar Train Station.
Then it's a 5 to 10 minute walk to the station.
Cheap KTM Komuter (commuter) trains leave Alor Setar for Butterworth every one or two hours.
From Butterworth train station, you then take the short ferry ride over to Georgetown on Penang Island.
Another option is to take the boat to Kuala Perlis, then take a bus from the nearby bus station to Butterworth bus station.
This way works our slightly more expensive and the Kuala Perlis to Butterworth / Penang bus is not that frequent and often fully booked.
The quickest way to get to Penang from Langkawi is to take a 40 minute flight from Langakwi Airport to Penang Airport.
If you plan ahead and book in advance, you can often find some good value seats on these planes.
Once you arrive at Penang International Airport, you can choose to take a taxi or RapidPenang bus in to Georgetown or anywhere else on the island.
If you have taken you car over to Langkawi Island, you will have to go back to the mainland the same way you came, via the Kuala Perlis car ferry.
Once you arrive in K. Perlis, the best way to travel by road is to head straight for the E1 North - South Highway, then drive all the way to Butterworth.
At Butterworth you can then decide to take the ferry to Georgetown, or go via the first Penang Bridge.