Interesting claim (on CBC's The Current, this morning) ...
All the gold that has ever seen the light of day, if assembled together and combined into a single 'lump', would be the size of a tennis court to a height of ca 35 feet (10.668 m).
Tennis court = 120 feet x 60 feet = 36.576 m x 18.288 m or 7,200 ft2 = 668.88 m2
Thus, a lump = 252,000 ft3 = 7,136 m3; this would be equivalent to a cube ~63 feet or ~19.25 m on a side.