How this calculation works
A soil sample contains solids, water and pore space. Water content expressed per dry-solid mass is different from water volume expressed per whole core volume. This page calculates both from the same measurements and makes their denominators explicit.
Gravimetric water = water mass/dry solids; volumetric water = water volume/core volume; porosity = 1 − dry bulk density/particle densityA worked example
The example has 100 g of dry solids after subtracting the 50 g container, and 30 g of water lost on drying. Gravimetric moisture is therefore thirty percent on a dry basis. In a 100 cm³ core at water density one, water occupies thirty percent of the whole volume. Dry bulk density is one g/cm³, and particle density 2.65 gives about 62.264 percent porosity and 48.182 percent pore saturation.
Good to know
Fixed-volume dry-basis arithmetic only; no preparation procedure, shrinkage correction, coarse-fragment model or laboratory certification. The inferred pore and water fractions depend on consistent masses and densities. They do not determine field capacity, infiltration rate or a watering recommendation.
Reference: USDA NRCS — soil water and density relationships (opens in a new tab) ↗
What the model answers
A soil sample contains solids, water and pore space. Water content expressed per dry-solid mass is different from water volume expressed per whole core volume. This page calculates both from the same measurements and makes their denominators explicit.
Dry bulk density includes the pore space in the measured core volume. Particle density describes only the dry particles. Their ratio therefore provides an ideal porosity estimate when the core and density assumptions are consistent.
The Crop stand count population calculator also relies on representative sampling, but it counts plants per observed area. Neither a core’s moisture value nor a stand count alone establishes crop yield.
Measure and enter consistently
Wet and dry totals must include the same container; tare is subtracted only from dry solids, while wet minus dry isolates the lost water mass. Dry total must exceed tare and wet total cannot be less than dry total.
Use a measured core volume that includes pores. Particle density and water density are supplied values, not inferred soil properties. Shrinking samples, coarse fragments or lost solids during preparation need additional corrections outside this model.
Interpret the result
Volumetric moisture cannot exceed the calculated pore volume in the supported model. The calculator rejects combinations that imply water beyond those pores or nonpositive porosity, because they indicate inconsistent measurements or assumptions.
Pore saturation is water volume divided by calculated pore volume. It is distinct from a crop’s plant-available water fraction; field capacity and wilting-point behavior are not supplied by a single gravimetric sample.
Work through the numbers
The example has 100 g of dry solids after subtracting the 50 g container, and 30 g of water lost on drying. Gravimetric moisture is therefore thirty percent on a dry basis.
In a 100 cm³ core at water density one, water occupies thirty percent of the whole volume. Dry bulk density is one g/cm³, and particle density 2.65 gives about 62.264 percent porosity and 48.182 percent pore saturation.
Where this model stops
Fixed-volume dry-basis arithmetic only; no preparation procedure, shrinkage correction, coarse-fragment model or laboratory certification.
The inferred pore and water fractions depend on consistent masses and densities. They do not determine field capacity, infiltration rate or a watering recommendation.
A few questions, answered
Why is dry-basis moisture different from wet-basis moisture?
Dry basis divides water mass by dry-solid mass; wet basis divides by total wet sample mass excluding the container.
Does saturation tell me plant-available water?
No. Pore filling and plant-available storage are different properties requiring additional measurements.