How long is a spartan spear?

That really depends what kind of spear you mean. In the 7th century BC, the Greeks evolved a new close-order infantry formation, the phalanx. The key to this formation was the hoplite, who was equipped with a large, circular, bronze-faced shield (hoplon) and a 7--9 ft. (2--2.75 m) spear with an iron head and bronze butt-spike (doru).

The 4th century saw major changes. One was the greater use of peltasts, light infantry armed with spear and javelins. The other was the development of the sarissa, a two-handed pike 18 ft. (5.5 m) in length.

The Macedonian xyston was 12--14 ft. (3.6--4.2 m) in length and could be used with one or both hands.

I found all this on Wikipedia, and there is much more information there, but I'm just filling you in on the basics.