According to Burl 'A brief history of Stonehenge' Thom made the Aubrey circle circumference 891 imperial feet (271.576m note; Burl looks like he rounded up to 272m). David has pointed out Thom has used another and I am not sure where Burl got his information however he is very clear in his book.
In any case this NUMBER 891 is the link as 89.1 Royal cubits 20.625ins (52.3875) = 1837.6875 ins 153.14062 imp feet or by 2 = 306.28124 feet (93.354525m) circumference and diameter = 97.492348 feet (29.715667m). Burl gave diameter a perfect circle 97.5 feet (29.718m).
Difference just over 1/10th of an inch.
copyright c jim wakefield