Understanding Wood Moisture

What is moisture content?

Moisture content (MC) is the weight of water in wood divided by the oven-dry weight, expressed as a percentage:

MC % = (wet weight − dry weight) / dry weight × 100

Fresh-sawn wood can be 30–60% MC; kiln-dried is typically 6–10%.

Equilibrium moisture content (EMC)

Wood stops exchanging moisture with air when it reaches EMC, which depends on temperature and humidity. Typical values:

Weight at any moisture

Density at MC = density-at-12% × (100 + MC) / 112
Weight = volume × density

So a board that weighs 10 kg at 12% weighs about 10.7 kg at 20% MC.

How much does wood move?

Shrinkage happens almost entirely across the grain (tangential most, radial less) and barely along it:

A 200 mm-wide oak board drying from 16% to 8% shrinks about 7–8 mm.

Practical tips

• Target 8–12% for indoor furniture; build at the MC the piece will live at.
• Acclimatize lumber 48+ hours before machining.
• Never fix solid wood rigidly — allow movement with figure-8 clips or floating panels.

Use the wood moisture calculator for exact weight and shrinkage numbers.