Calibre

the diameter of something of circular section, especially that of the inside of a tube:
a pipe of three-inch caliber.
Ordnance. the diameter of the bore of a gun taken as a unit of measurement.
degree of capacity or competence; ability:
a mathematician of high caliber.
degree of merit or excellence; quality:
the high moral caliber of the era.
Contemporary Examples

Taliban: Harry Comparing War to Xbox Demeans Him Tom Sykes January 21, 2013
How Can Romney Recover? David Frum October 16, 2012

Historical Examples

The Advance of Science in the Last Half-Century T.H. (Thomas Henry) Huxley
Gallipoli Diary, Volume 2 Ian Hamilton
The Modern Pistol and How to Shoot It Walter Winans
Robert Orange John Oliver Hobbes
Blackwood’s Edinburgh Magazine, No. 401, March 1849 Various
Man on the Ocean R.M. Ballantyne
With a Reservist in France F. A. Bolwell
The Letters Of Mark Twain, Volume 1, 1853-1866 Mark Twain (Samuel Clemens)

noun
the diameter of a cylindrical body, esp the internal diameter of a tube or the bore of a firearm
the diameter of a shell or bullet
ability; distinction: a musician of high calibre
personal character: a man of high calibre
n.
n.