Moisture content definition — the water content of a soil is defined as the ratio of:

Introduction / Context:
Water content (also called moisture content) is a fundamental index property used in compaction control, strength correlation, and phase relationship calculations. A precise definition avoids confusion with volumetric moisture or degree of saturation, which are different measures.

Given Data / Assumptions:

• Standard geotechnical definition is used.
• Mass (or weight) basis is assumed, consistent with laboratory measurements.
• Sample is representative and contained before weighing to prevent moisture loss.

Concept / Approach:

Water content w (%) is defined as w = Mw / Ms * 100, where Mw is the mass (weight) of water in the pores and Ms is the mass (weight) of dry soil solids. It is not based on volumes in its standard definition, and it does not involve the mass of air, which is negligible in soil pores for most practical purposes.

Step-by-Step Solution:

Verification / Alternative check:

Repeat oven-dry cycles to ensure constant mass; cross-check with rapid field methods and correct for bias if necessary.

Why Other Options Are Wrong:

Volume ratios correspond to volumetric water content or degree of saturation, not standard w.

Weight of air is not used; air mass is negligible and impractical to measure.

Common Pitfalls:

Accidentally using total mass in the denominator; letting the specimen lose moisture before wet weighing; mixing volume and mass bases.

Final Answer:

weight of water to weight of solids in the given soil mass