How many strings does a standard concert grand pedal harp have?

How to get close to this number

Multiply octaves by notes. The explanation gives the range as six and a half octaves, and a harp has one string per note of a diatonic scale — seven per octave rather than the twelve of a chromatic keyboard. Six and a half times seven gives the answer.

That diatonic stringing is the key structural difference from a piano. A harp has no black keys; every string is a natural note of one scale, which means it cannot play chromatically without a mechanism. Understanding that is what makes the pedal system comprehensible rather than mysterious.

And the pedals are the mechanism, as the explanation says: seven pedals, one per note name, each re-tuning every string of that pitch by a semitone at once. So an instrument that can only play one scale at a time can change which scale mid-performance, using the feet while the hands keep playing. It is one of the most ingenious mechanical solutions in any instrument.