Moisture content: dry basis and wet basis

Two definitions

Moisture content (MC) compares the mass of water with a reference mass:

• Dry basis (used in the timber trade): MC = (m_wet − m_dry) / m_dry × 100
• Wet basis (used for fuel wood and some industries): MC = (m_wet − m_dry) / m_wet × 100

Example: a sample weighs 120 g and 100 g after oven drying. Its MC is 20 % on the dry basis and 16.7 % on the wet basis.

Why it matters

Always state which basis is meant. On the dry basis, MC can exceed 100 % in very wet wood; on the wet basis it cannot.

Oven-dry mass

The reference dry mass comes from drying a sample in an oven until the mass stops changing, using the procedure of the applicable standard. A handheld moisture meter gives an indirect estimate and needs correction for species and temperature.

You can compute both values with the Timber moisture calculator.