# How is “wing thickness” defined?

In the answers to this question about wing thickness, there were many references to wing thickness as a percentage (ranging from 6.5% to 13.5%).

What is that a percentage of?

The wing thickness is basically the distance between the upper and lower surface of the wing (or airfoil).

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Source: NASA.

The wing thickness is usually given as a percentage of the wing (or airfoil) chord(the distance between the leading and trailing edge). This is to make it a non-dimensional quantity for ease of comparison across different scales.

• The picture really helps with understanding. Thanks. – FreeMan Aug 20 '15 at 16:12