I could use some more information, What kind of cable? (All coax is not created equal)
How long are the runs? How are you splitting the signal? What is the frequency range of the splitter your using ? How many runs are hooked up? How are you boosting the signal?
All of these make a difference.
The easiest way to check the signal is with one TV hooked to the cable at the point where the cable comes into the house (not splitter). Radio Shack makes a cheap RF adjustable attenuator, use it between the TV and cable. If all the channels work ok, start adding more attenuation until the signal gets bad. Most TV's (Not perfect) start to show a bad picture at -10 db. Based on your attenuation setting and the TV picture your can kinda figure what the signal strength is coming in. You would like to see between 0 and 10 coming into the house. 0 being not great but workable and 10 being the "The great white hope".
Good luck