The inside of the hatband of this hat measures 58cm or 22¾", that is size 7⅛ in UK hat sizes or 7¼ in the USA
The hat is in very good condition.

Inside the hat has a leather band embossed "Woodrow Amylyte Birmingham"
Amylyte was a lightweight waterproof material developed by Woodrow in the 1930's, please look at the image of the advert from the 1933 Polo Yearbook.
Inside the crown of the hat it  is stamped "Ridley & Nivock, 33/35 London St., Norwich" and shows Woodrow's royal warrant to Queen Elizabeth II - so the hat must date between her coronation in 1952 and the closing of Ridley & Nivock, which seems to have happened in the late 1960's.

The outside of the hat is in excellent condition and has its original ribbon band

Hat size : Height of crown (approx): 4¾ inches (12cm)
Interior Circumference : 22.6" (58cm)
Interior Width : 6⅛" (16cm)
Interior Depth (front to back): 8" (20.4cm)
Weight 3oz (86g)

Please ask for any other measurements that you require

Ref : Bowler024