Water (Moisture) Content

The single most-run test in any soils laboratory: weigh the tin wet, dry it overnight at 110 ± 5 °C, weigh it again, and the difference is water. A sample losing 45 g from 295 g of wet soil leaves 250 g of solids, so w = 45 ÷ 250 × 100 = 18%. Everything downstream — dry unit weight, saturation, compaction control, Atterberg indices — is built on this number, which is why the tin is weighed to 0.01 g and why the balance is the first thing a technician calibrates.

The trap is in the denominator: water content is referred to the mass of dry solids, not to the total wet mass. Divide by the wet mass and you have computed something a mining engineer would call moisture and a soils engineer would call wrong, and the two differ by 15% at w = 18%. That definition is also why w can legitimately exceed 100% — a Norwegian quick clay or a Florida peat can hold two or three times its own dry weight in water, giving w = 250% with no arithmetic error anywhere. Do not "fix" such a number.