Sample Water Content Calculator
Written by Thierno Sadou Diallo, formula verified per our methodology • Last checked on 10/10/2026
Water content on a wet basis is calculated with (fresh weight − dry weight) ÷ fresh weight × 100. For a leaf weighing 10 g fresh and 2 g once dried, the wet-basis water content is 80%.
Explanation
The water content of a biological sample (a leaf, animal tissue, a soil sample, food) is measured by comparing its weight before and after complete dehydration (usually in an oven, until the weight stops changing). Two calculation conventions coexist in the scientific and technical literature, and confusing them is a common source of error: wet-basis content, the most widely used in biology and food science, relates the mass of water lost to the starting FRESH weight, which always constrains it between 0 and 100%; dry-basis content, more commonly used in the wood or textile industry, relates that same lost water mass to the final DRY weight, which lets it exceed 100% for a sample very rich in water (a leaf at 80% water on a wet basis thus shows 400% on a dry basis, since the mass of water lost is then four times greater than what remains as dry matter). This calculator gives both values at once, precisely to avoid this confusion between the two conventions when reading a publication or technical sheet that doesn't always specify which one is used. A plant tissue's water content varies greatly by species, organ, and environmental conditions (a fresh leaf typically contains 70 to 90% water on a wet basis, a dry seed often less than 15%), making it a useful indicator for comparing samples to each other or tracking an organism's water status over time — including assessing the quality of a seed lot before a germination rate test, since an overly moist seed is more prone to mold during storage. Once the dry weight is known, it also lets a compound's mass concentration be expressed relative to dry matter rather than fresh weight, a more stable reference for comparing samples with different water contents.
Example: a leaf weighing 10 g fresh, 2 g dry
Inputs
Fresh weight: 10 g. Dry weight: 2 g.
Calculation
Wet basis = (10 − 2) ÷ 10 × 100 = 80%. Dry basis = (10 − 2) ÷ 2 × 100 = 400%.
Result
This leaf contains 80% water on a wet basis (the most common convention), or 400% on a dry basis.
Frequently asked questions
Which convention (wet basis or dry basis) should I use?
Wet basis is the most widespread convention in biology, ecology, and food science, since it always stays between 0 and 100%, making it more intuitive to interpret. Dry basis is preferred in certain industrial sectors (wood, textiles, agriculture for ration calculations), notably because it simplifies certain dilution or mixing calculations expressed relative to dry matter. Absent any indication otherwise in a given context, wet basis is generally the expected default value.
Why can dry-basis water content exceed 100%?
Because it relates the mass of water lost to the final DRY weight, not the starting fresh weight: if a sample loses more water than the dry matter it has left (common for tissues very rich in water, like a leaf or fresh fruit), the ratio mechanically exceeds 100%. This isn't a calculation error, simply the mathematical consequence of this different convention.
How do I obtain a sample's dry weight?
The reference method is to place the sample in an oven at a controlled temperature (generally 60 to 105°C depending on the sample type, to avoid degrading heat-sensitive compounds) until its weight no longer changes between two successive weighings, a sign that all evaporable water has been removed. A desiccator with a drying agent can also be used for small, heat-sensitive samples.