Almighty Calculator

Wood Moisture Content and Drying Weight Calculator

Wood moisture content (dry basis) is (wet weight − oven-dry weight) ÷ oven-dry weight × 100; weight at a target moisture is oven-dry weight × (1 + target ÷ 100).

lb
%
Dry-basis percent, as a moisture meter reads. Used for “weight and moisture content”.
lb
Used for “weight and oven-dry weight”.
%
For example, the moisture content you want after drying.
Weight at target moisture
89.6lb
Oven-dry weight80 lb
Moisture content (dry basis)25 %
Moisture content (wet basis)20 %
Water to lose by drying10.4 lb

Show the math

Oven-dry weight = 100 lb ÷ (1 + 25 ÷ 100) = 80 lb
Wet-basis moisture = (100 − 80) ÷ 100 × 100 = 20%
Weight at 12% = 80 × (1 + 12 ÷ 100) = 89.6 lb
Water to lose = 100 − 89.6 = 10.4 lb

Rounded the same way as the result above.

How it works

Wood moisture content is the weight of water as a percent of the oven-dry weight of the wood, the way moisture meters and the USDA Wood Handbook report it. It can exceed 100% in green wood. Firewood sellers often quote wet basis instead, where water is a percent of the total weight.

Knowing the oven-dry weight lets you predict the weight at any other moisture: it is that weight times one plus the moisture content. The difference from the current weight is the water you need to dry out.

MC (dry basis) = (W − W_od) ÷ W_od × 100 W_od = W ÷ (1 + MC ÷ 100) MC (wet basis) = (W − W_od) ÷ W × 100 Weight at target = W_od × (1 + target ÷ 100)

Worked example

A 100 lb load of lumber at 25% moisture, dried to 12%:

  1. Oven-dry weight = 100 lb ÷ (1 + 25 ÷ 100) = 80 lb
  2. Wet-basis moisture = (100 − 80) ÷ 100 × 100 = 20%
  3. Weight at 12% = 80 × (1 + 12 ÷ 100) = 89.6 lb
  4. Water to lose = 100 − 89.6 = 10.4 lb
InputValue
I knowCurrent weight and moisture content
Current weight100 lb
Current moisture content (if known)25 %
Oven-dry weight (if known)80 lb
Target moisture content12 %
ResultValue
Weight at target moisture89.6 lb
Oven-dry weight80 lb
Moisture content (dry basis)25 %
Moisture content (wet basis)20 %
Water to lose by drying10.4 lb

Assumptions and limits

  • Moisture content here is dry basis, as in the Wood Handbook. Wet-basis percent is shown separately.
  • Oven-dry weight ignores tiny losses of volatile extractives; the Handbook’s definition uses oven drying to constant weight.
  • Predicts weight from moisture only; it does not model shrinkage of the piece.

Common questions

How do I calculate wood moisture content?

Subtract the oven-dry weight from the wet weight, divide by the oven-dry weight, and multiply by 100.

Why can moisture content be over 100%?

Dry basis divides by the dry weight. A log with more water weight than wood weight is over 100%.

What is the difference between wet and dry basis?

Dry basis uses oven-dry weight as the base; wet basis uses the total weight. Wet basis is always lower and can never pass 100%.

How much weight does lumber lose when drying?

Enter the current weight and moisture content and a target moisture; the calculator shows the water to lose.

Sources

  • USDA Forest Products Laboratory, Wood Handbook (FPL-GTR-282), Chapter 4: moisture content equation (Eq. 4-1).
  • Wet-basis percent is the water weight divided by total weight.

Updated 2026-09-30