High Quality Content by WIKIPEDIA articles! In mathematics, Stirling's approximation (or Stirling's formula) is an approximation for large factorials. It is named after James Stirling.James Stirling (May 1692 December 1770) was a Scottish mathematician. He was educated at Balliol College, Oxford where he was a Snell exhibitioner. The Stirling numbers and Stirling's approximation are named after him.