The jar has a radius of 6" and a height of 24" and each ball has a radius of 1".

So I found the volume of the jar which is $\displaystyle \pi6^{2}(24) = \approx 2,714.33605$ and the volume of the balls which is $\displaystyle \frac{4}{3}\pi1^{3} = \approx 4.1887902$

And then I divided how many of the balls can go into the jar by dividing:

$\displaystyle 2714.33605 \div 4.1887902 = 648 balls$

Does that number take into account the spaces between the balls when put into the jar? Like the small gaps when spheres are placed next to each other.