Jerry,

If you take 2 pills containing 250 mg of active ingredient then you have
taken 500 mg of active ingredient.
The inactive ingredients may be important though. So be sure that these
are the same type of pills.Some pills are gel caps, some are slow release,
some are enteric coated, some are chewable or designed for quick absorbtion,
et c.
Don't expect 2 slow release 250 mg pills to have the same effect as a
500mg fast release pill.

Dave M.