The LengthSplit command splits a list L into a sequence of sublists, each with n elements. If n does not divide evenly into $\mathrm{nops}\left(L\right)$, then the final sublist will have $\mathrm{irem}\left(\mathrm{nops}\left(L\right)\,n\right)$ elements, unless the $\mathrm{pad}=\mathrm{expr}$ option is given, in which case the value of expr will be used to fill out the final sublist to length $n$. If $n$ divides evenly into $\mathrm{nops}\left(L\right)$, then the pad option has no effect.

$\mathrm{with}\left(\mathrm{ListTools}\right)\:$

$L≔\left[\mathrm{seq}\right]\left(i\,i=1..12\right)$

$L≔\left[1\,2\,3\,4\,5\,6\,7\,8\,9\,10\,11\,12\right]$

$\mathrm{LengthSplit}\left(L\,3\right)$

$\left[1\,2\,3\right],\left[4\,5\,6\right],\left[7\,8\,9\right],\left[10\,11\,12\right]$

$\mathrm{LengthSplit}\left(L\,4\right)$

$\left[1\,2\,3\,4\right],\left[5\,6\,7\,8\right],\left[9\,10\,11\,12\right]$

$\mathrm{LengthSplit}\left(L\,5\right)$

$\left[1\,2\,3\,4\,5\right],\left[6\,7\,8\,9\,10\right],\left[11\,12\right]$

$\mathrm{LengthSplit}\left(L\,5\,'\mathrm{pad}'=x\right)$

$\left[1\,2\,3\,4\,5\right],\left[6\,7\,8\,9\,10\right],\left[11\,12\,x\,x\,x\right]$