Unfortunately there are no standards for surge protection capacity.
The are three basic things that can go wrong with AC power; 1) Sag, 2) Spike, and 3) Surge.
A surge protector will handle minor power surges; these surges occur when devices are switched ON and OFF in the home as well as in the neighborhood.
A surge protector will not handle any sags. A UPS system will help.
Spikes will not be handled by a surge protector very well. UPS will help.
A good analogy is comparing surges to 'High Tides', 'Tidal Waves' and finally the worst 'Tsunami'.
To summarize, a decent Tripp Lite (or similar) surge protector will be good enough for most home devices.
During a thunderstorm, UNPLUG devices from the wall outlet. I have more than one computer and it is inconvenient but I do this during thunderstorms. Merely switching them OFF will not be good enough. A Lightning strike can easily jump across terminals in any switch/outlet.
Here is more information on the topic: http://www.surgeassure.com/faq.aspx