Soil Moisture Content
Gravimetric water content of soil by weight.
Formula
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Example
Wet 240 g, dry 200 g: θ = 20%
How it works
This formula tells you how much water is in a soil sample compared with the mass of the dry soil alone. You first find the extra mass due to water by subtracting the dry mass from the wet mass, then divide by the dry mass so the result is expressed as a percentage of the soil’s solid matter. It works because drying removes only the water, so the mass difference is the water mass.
When to use it
Use this when you need the gravimetric moisture content of soil from a lab sample, such as in agriculture, irrigation planning, or soil testing. It is useful whenever you have weighed the same soil before and after oven-drying.
Worked example, step by step
Wet soil mass, m_w = 180 g Dry soil mass, m_d = 150 g Water mass = m_w - m_d = 180 - 150 = 30 g θ = (m_w - m_d) / m_d × 100 θ = 30 / 150 × 100 θ = 20% Final answer: the soil moisture content is 20%
Common mistakes to avoid
- Dividing by the wet mass instead of the dry mass
- Using a sample that was not fully dried, which makes the moisture content too low
- Forgetting to convert the difference in mass into a percentage
Did You Know?
Knowing soil moisture stops farmers watering land that's already wet enough — saving water and roots.
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