It's pretty easy for a matrix that you know was originally constructed from a rotation and uniform scale - just take the columns / rows of the matrix and treat them as 3-vectors and find their length. If the matrix is constructed from a rotation and uniform scale all the lengths should be the same to within a small tolerance. The length is the scale and if you divide through by the scale you get back the original rotation matrix. The same principle applies for non-uniform scale but you have a different scale on each axis and you also then have to know whether the scale or the rotation was applied first.

I think this will be better discussed in 'Maths & Physics' - moved. [smile]

For a DirectX-oriented 'answer' you might want to look at the various D3DX maths functions; I don't have my docs to hand, but I'm pretty sure there are some decomposition functions that can break down an arbitrary matrix into the component SRT parts...

hth
Jack