I'm operating on the assumption that you aren't going to use this tool on a regular basis.

If you are, don't read the rest of this post; go buy a field strenth meter.

If it's a one time deal, take the cheap way.

Go to the demarcation point (where cable comes into the house). Discconnect the splitter mechanism AFTER labeling your wires. Hook up a small tv and check for signal strength. Does the picture look good on all your channels? If no, you need to talk to the cable folks and have them increase the signal coming in to the house. If yes, then add an amplifier. What size? Look at the splitter/splitters; remember that splitters diminish signal strength. For crude purposes, a 2 way takes away 4 dB; an 8 way takes away 12 dB. You want to compensate for the loss that the splitter network causes. Remember, signal also is lost over distance, so if the house is big, subtract about 6 dB for each 100 feet.