Kinect raw depth to distance in meters

The correct answer is actually a comment on your question. The number given is actually a distance in millimetres. To get this number, you either need to use a skeleton joint and call DepthImageFrame’s MapFromSkeletonPoint or shift the raw short value right by DepthImageFrame.PlayerIndexBitmaskWidth.

E.g. Skeleton

using (var skeletonFrame= e.OpenSkeletonFrame())
using (var depthFrame = e.OpenDepthImageFrame())
{
    skeletonFrame.CopySkeletonDataTo(skeletons);
    var skeletons = new Skeleton[skeletonFrame.SkeletonArrayLength];

    foreach (var skeleton in skeletons)
    {
            if (skeleton.TrackingState != SkeletonTrackingState.Tracked) continue;

            var head = skeleton.Joints[JointType.Head];
            if (head.TrackingState == JointTrackingState.NotTracked) continue;

            var depthImagePoint = depthFrame.MapFromSkeletonPoint(head.Position);

            int depthInMillimeters = depthImagePoint.Depth; // TADA!
    }
}

E.g. shift

using (var depthFrame = e.OpenDepthImageFrame())
{
    var depthArray = new short[depthFrame.PixelDataLength];
    depthFrame.CopyPixelDataTo(depthArray);

    for (int i = 0; i < depthArray.Length; i++) {
        int depthInMillimeters = 
            depthArray[i] >> DepthImageFrame.PlayerIndexBitmaskWidth;
        // TADAx2!
}

The original solution below is no longer correct:

Based on the contents of this article – http://openkinect.org/wiki/Imaging_Information:

if (depthValue <= 2047) {
   depthM = 0.1236 * Math.Tan(depthValue / 2842.5 + 1.1863);
}