Moisture Content Calculator (dry basis & wet basis from wet and oven-dry weight)

Understanding the moisture content calculator — concept and principle

This calculator works out the moisture content of a sample on a dry basis and a wet basis from its wet and oven-dry weights, and tells you how much water must be removed (or added) to reach a target moisture. It is used for wood and firewood, soil, grain, hay, food drying and building materials.

Water against dry weight: with the default inputs the result is 25% dry basis (= 20% wet basis).

How it is calculated

Water = wet weight − oven-dry weight.
Dry basis MC = water ÷ dry weight × 100 (used for wood and soil; can exceed 100%).
Wet basis MC = water ÷ wet weight × 100 (used for grain and food; always below 100%).
Conversion: MC_wet = MC_dry ÷ (1 + MC_dry).
Weight at a target (dry basis) = dry weight × (1 + target).
Water to remove = wet weight − target weight.

The principle

A material's dry matter does not change as it dries; only the water does. So the dry weight is a fixed reference, and moisture content on a dry basis is simply water per unit of dry matter. That is why wood scientists use it: weight at any moisture is dry weight × (1 + MC). Grain and food trades use the wet basis, water as a share of the whole sample, because they sell by total weight. The oven-dry weight is found by drying a sample in an oven until its weight stops changing.

Worked example

Default inputs: wet weight 125 g, oven-dry weight 100 g, target 12% (dry basis).

Water = 125 − 100 = 25 g.
Dry basis = 25 ÷ 100 = 25%.
Wet basis = 25 ÷ 125 = 20%.
Weight at 12% = 100 × 1.12 = 112 g, so remove 125 − 112 = 13 g of water.
Target as wet basis = 12 ÷ 112 = 10.7%.

How to read the result

Always state which basis you mean, because the same sample has different figures: here 25% dry basis equals 20% wet basis. Use the "water to remove" figure to judge how much more drying is needed.

Common mistakes

Comparing a dry-basis figure with a wet-basis target.
Using an air-dried weight as the oven-dry weight.
Weighing a sample that has picked up or lost water since collection.
Treating a pin-meter reading as exact for all species.

Keep in mind: Moisture meters and drying methods differ; for official grading or trading, follow the relevant standard test method.

Frequently asked questions

What is the difference between dry-basis and wet-basis moisture?

Dry basis divides the water by the dry weight; wet basis divides it by the total weight.

How do I convert dry-basis moisture to wet basis?

MC_wet = MC_dry ÷ (1 + MC_dry); 25% dry basis is 20% wet basis.

How do I find the dry weight?

Dry a sample in an oven until its weight stops changing.

Sources: Penn State Extension, "Calculating the Green Weight of Wood Species" (after USDA FPL Wood Handbook)

Checked 9 Nov 2026. Dry-basis definition MC = (m_green − m_dry) ÷ m_dry and green weight = dry weight × (1 + MC): Penn State Extension, “Calculating the Green Weight of Wood Species” (after USDA FPL Wood Handbook); wet basis = water ÷ total mass (definition).

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