What size filter lens do I get for these lenses?

NikonDSLR D5000
-18-55mm f/3.5 - f/5.6 DX Nikkor lens
-Nikkor 55-200mm f/4-5.6G ED AF-S DX Zoom Lens

It is marked on the front of the lens. You will see xxΦ (52Φ/58Φ/72Φ), that is your filter and cap size in millimeters for that particular lens.

As BEI said. If you do not have the lens, you can go to the Nikon website and look up the stats on the lens which will tell you the filter thread size.

Both take 52mm filters