This is copied directly from a PDF on Morewine.com,
click here to open the full PDF.
The amount to add is as follows:
Oak Chips -.1 to .2 grams per liter
Oak Cubes - 2 to 2.5 ounces of oak cubes per 5 gallons of liquid wine.
The difference in how fast the oak is extracted :
• Chips (around 7 days)
• Cubes (2 months minimum, up to 1 year of useful life)
• Segments (3 months minimum, 18 months of useful life)
• Staves (3 months minimum, useful life of 2 years)
Remember, the amount of oak is a personal preference, the oak will dissipate slowly with time so waiting until the oak is just beyond what you enjoy is a good practice, when adding oak, adding it during fermentation is the best time to add it, the yeast metabolizes and buffers the oak much like a barrel fermentation (Thanks to Bzac for that tip), and last but not least....Nothing compares to barrel aging, you will be amazed at how much the wine will improve in a barrel.
I hope that this helps.