Construction & DIY · Woodworking
Wood moisture content calculator.
Moisture content from a weighed sample, and the weight a piece should reach when it has dried to your target.
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Enter the weights.
How do you calculate the moisture content of wood?
The USDA Wood Handbook defines moisture content on an oven-dry basis: the mass of water in the wood divided by the mass of the oven-dry wood, expressed as a percentage. So MC = (weight now − oven-dry weight) / oven-dry weight × 100. Because the divisor is the dry weight, moisture content can exceed 100% in very wet wood.
Worked example. A sample weighs 120 g and 100 g after oven drying: MC = 20 / 100 = 20%. To find what a 120 g piece at 20% should weigh at 8%, first get its dry weight, 120 / 1.20 = 100 g, then multiply by 1.08 for 108 g, so 12 g of water still has to leave.
Weights can be in any unit as long as you use the same one throughout. Oven drying is a laboratory-style method; a moisture meter is the usual shop check, and its species and temperature corrections are in the meter's own manual.
Frequently asked questions
What is the formula for wood moisture content?
Moisture content (%) = (weight now minus oven-dry weight) divided by oven-dry weight times 100. This is the oven-dry basis used by the USDA Wood Handbook.
Can wood moisture content be over 100%?
Yes. The divisor is the oven-dry weight, so wet wood can hold more water than wood substance. The Wood Handbook lists green moisture contents above 100% for some species.
How do I know what a board should weigh when dry?
Divide its current weight by one plus its current moisture content as a decimal to get the oven-dry weight, then multiply by one plus the target moisture content. The second calculator above does this.
Is a moisture meter more convenient than weighing?
Usually, but meters need species and temperature corrections given in their manuals, and readings are less reliable above fiber saturation. Weighing a sample is the reference method.
Sources
Checked
The moisture content definition (mass of water over oven-dry mass) is from Chapter 4 of the Wood Handbook. The target-weight step is algebra from that definition. Meter guidance is general and not from a published table. Runs entirely in your browser. Nothing you type is sent or stored.
Scope
For planning and learning. Always follow your meter or lab procedure for critical moisture checks, such as flooring or kiln-drying work.