I am re-wiring an eight light chandelier that was wired in a series. I would like a formula to figure the maximum wattage for a given wire, or the wire size required to obtain a certain maximum wattage. Would the formula also work if the chandelier was not wired in series?

I have included a link for awire chart; http://www.armstrongssupply.com/wire_chart.htm.
Wire ampacity is determined by the National Electric Code.

For most light fixtures, #16 THHN is typically used, since larger wire may not fit through the fixtrue tubing.

Are you sure the fixture was wired series? If so , not very practical to rewire it that way again. Any lamp that burns out will open the entire circuit and all the lamps will go out. All light fixtures in the US are wired in parallel, so when one lamp burns out all the others stay on.

Convert your wattage into amperes using the following formula:

P=EI
P= Power or Wattage
E=Voltage
I= Amperes

When power and voltage is known invert fomrula to I=P/E

For example, assume you have eight 100 watt lamps, and the voltage is 120 volts.
I=P/E
I=800 watts divided by 120 volts
I= 6.7 amps

Hope this helps. If not get back to me with more details