The amount of moisture in wood is termed the moisture content. It can be expressed as a percentage of either dry or wet weight. For most purposes, the moisture content of lumber is based on the dry weight and the moisture content of wood fuel is usually based on the wet weight.
Moisture content on dry and wet basis is described as follows:
On a dry basis:
Moisture content (percent) = ( Weight of water / Weight of totally dry wood ) x 100
On wet basis:
Moisture content (percent) = ( Weight of water / Weight of totally dry wood and water ) x 100
The two ways of expressing moisture content can be related by,
Moisture content (dry basis) = [ moisture content (wet basis) / 100-Moisture content (wet basis) ] x 100
From: Dry Kiln Operators Manual
