Motorcycle inner tube question?

I just bought a used bike that has spoke wheels. I'm shopping for new tires online and apparently I need inner tubes for each tire. The only problem is I dont know how the sizing works. My front tire is 110/80r18 and the rear is 150/80r16.
But I dont know how to find corresponding innertube sizes.
I was looking on denniskirk.com and It would say stuff like, "fits tire size 100/100, 120/100... do I need to find something that says "fits 110/80? ..because I can't. I've also found tubes that say, "fits 3.25.3.50/4.10/4.25" I dont know wha this means...please help!
Thanks!

I'm not installing the tires myself. I'm taking them to a shop but I wanted to buy the tires and tubes online. I found some tubes that seem to be a perfect fit but they are $25.00 each. Apparently the SAE tubes go by rim width. If the tube is an 18x 4.5, Does that mean that if the tube fits any tire that's on an 18" rim that 4.5" wide?

Use this metric/inch tire size conversion chart.
http://www.kendausa.com/_includes/Conver...

If you cannot find the exact tube size, always use a smaller size, not a larger one.

The largest # is the width of the tire / then the height of the tire from the rim to the tread - rim diameter is the last #
The width of the tire will determine the tube size.

seems to be a bit expensive for tubes. I just bought two at a bike shop for $10 each.

the numbers listed at the bottom of your questions are RIM widths

First off, a 110/80-18 tire is 110 mm wide (approx 4.4 inches), the height of the tire from the bead to the tread is 80% (called aspect ratio) of the width, so it's approx 88mm tall (3.5 inches) and the wheel is 18 inches in diameter.

Tubes stretch a certain amount and therefore one size tube will fit several different size tires. A tube that says fits 3.25-3.50 X 18 means it will fit tires with a width of 3.25-3.5 inches with a wheel diameter of 18 inches. Tubes have a round cross section, so the aspect ratio of the tire isn't all that important.

same as the tire

Besides inner tubes you will need rim liners. They are a strip of rubber that goes between the rim and the tube so that the ends of the spokes don't abrade the tube.
Your best bet is to go to a shop for the tires and installation. Find a good independent (non-dealer) shop near you. Their prices and labor charges are lower than the dealers.
If you buy the tires yourself are you capable of removing the wheels, removing the tires, mounting the tires, balancing them, and reinstalling the wheels SAFELY? Do you have a torque wrench? If you answered no to any of the above you should go to a shop, it's worth the money.