Wood Moisture Content Calculator
MC, basis conversion and drying-outcome — Wood Handbook 2021 equations.
Pick a mode: (1) sample — enter wet + oven-dry mass and get MC on both bases; (2) drying — start mass + start MC + target MC and get final mass, oven-dry mass and water lost; (3) max — basic density returns the maximum cell-wall-saturation MC and the float/sink MC. The Wood Handbook 2021 Eq. 4-2 is W₂ = W₁ × (100+MC₂)/(100+MC₁) — note that MC₁ must be entered on the same basis as MC₂ (oven-dry or wet).
FAQ
What is the difference between MC on oven-dry and wet basis?
Oven-dry (od) is mass of water ÷ oven-dry mass × 100 — the industry default in lumber, kiln and forestry. Wet basis (wb) is mass of water ÷ wet mass × 100, common in soil science. 30% MC od = 23.08% MC wb; they are interchangeable. This calculator accepts both and converts internally.
Why does the drying formula keep the dry mass constant?
Because the wood substance itself doesn't change while drying — only water leaves. Dry mass = wet mass × 100 ÷ (100 + MC_od). So 500 kg at 60% MC contains 312.5 kg of dry wood; dried to 12% MC the same wood weighs 350 kg. The 'inverse' formula (1+MC₁)/(1+MC₂) shown in some online references is wrong: it would give 714 kg, which is impossible.
Can MC go above 100%?
Yes, on the oven-dry basis. Tropical hardwood sapwood (e.g. freshly felled eucalyptus) often reaches 100–150% MC. Above 100% the wood contains more water than wood substance. The theoretical maximum (when all cell cavities are also full) is MCmax = 100 × (1.54 − Gb)/(1.54 × Gb) using Gb in g/cm³ — for acacia mangium (Gb 0.56) that's about 105%; for lighter species like spruce (Gb 0.36) it reaches 213%.
What moisture content should lumber be before furniture making?
Eight to ten percent for furniture bound for heated interiors, about 12% for general indoor joinery. The target is the wood's equilibrium moisture content where the piece will live, not a universal number.
How is moisture content on the dry basis calculated?
MC = (wet mass − oven-dry mass) ÷ oven-dry mass × 100. Because the reference is the dry mass, values above 100% are perfectly normal for fresh wood — the water can outweigh the dry cell walls.
What is the fibre saturation point?
Around 28–30% MC (about 22% for the teak group) — the point where cell cavities are empty but cell walls are still saturated. Below FSP, wood starts to shrink; above it, moisture moves without changing dimensions.
Why do boards check or crack while drying?
The shell dries below the fibre saturation point and tries to shrink while the wet core holds it apart — the surface splits under that tension. Slow the schedule, sticker the stack for airflow, and seal end grain, where moisture escapes fastest.
How long does air drying take?
The old rule of thumb is about one year per 25 mm of thickness for hardwoods, faster for softwoods and in dry, windy climates. Kilns compress the same journey to weeks — at the price of energy and schedule discipline.
What is equilibrium moisture content (EMC)?
The MC wood settles at for a given humidity and temperature: indoors roughly 6–10%, unheated outbuildings higher. Wood kept above its future EMC will shrink in service — which is how furniture gaps and loose joints happen.
How accurate are pin moisture meters?
Good meters read within about 1–2 percentage points in their calibrated range, with species and temperature corrections applied. The oven-dry method remains the reference; meters are for fast, non-destructive routine checks against it.
Can plantation acacia or eucalyptus be kiln-dried?
Yes — both are kiln-dried at scale in Vietnam and elsewhere. They demand milder schedules and careful monitoring because growth stresses, collapse and twist show up when drying runs fast or hot.
How much lighter is 12% wood than green wood?
About a third lighter across common species: spruce falls from ≈ 640 kg/m³ green to ≈ 420 at 12% MC, acacia from ≈ 970 to ≈ 660–700. Weight, like dimension, tracks moisture.