Ta Rhiannon for your nice comments. In one of my pics of Coldrum(not posted) my aged Ma is leaning against the fence but she is too far away from the stones to give a scale.
Moth, I think that you underestimated the size of the stones in the chamber as the ground level inside is below the level of the main mound. I would estimate as between 7 and 8ft.
Smaller stones are easy to get a scale from, leaves,grass and wild flowers etc but how to get a scale for the larger without it looking contrived and/or ugly is a bit of a poser.
Jim.