you should find your gap size on the sticker under the hood and on the crossbar above the radiator, if you can still read it, or in your haynes manual. All you need are some feeler gauges and a pair of pliers to bend the tip. Most the time the gaps are already close enough not to worry about.
I figure anyone inclined to change their own plugs would also be incline to buy a service manual, but then again I see people trying to change out alternators, PS pumps, starters, AC compressors and change their oil and tranny fluid in the parking lot of AutoZone, asking questions every step of the way. I think some of these parts stores should just rent out garage space.