What is volumetric water content (VWC)?

VWC is the volume of water per unit volume of soil, expressed as a decimal or percentage. For example, VWC = 0.25 means 25% of the soil volume is occupied by water. Most soil moisture sensors (capacitance, TDR, FDR) report VWC directly. It is the most practical unit for irrigation scheduling.

What is the difference between field capacity and wilting point?

Field capacity (FC) is the soil moisture content after free drainage has ceased (typically 1–3 days after saturation). The permanent wilting point (PWP) is the moisture level at which plants can no longer extract water and wilt permanently. The range between FC and PWP is called plant-available water capacity (AWC).

How do I convert gravimetric moisture to volumetric moisture?

VWC (m³/m³) = Gravimetric moisture (g/g) × Bulk density (g/cm³) ÷ 1.0 (density of water). For example, 20% gravimetric moisture with a bulk density of 1.35 g/cm³ gives VWC = 0.20 × 1.35 = 0.27 or 27%.

What bulk density should I use if I don't have lab data?

Typical ranges by texture: sandy soils 1.55–1.80 g/cm³; sandy loam 1.40–1.60 g/cm³; loam 1.20–1.45 g/cm³; clay loam 1.15–1.35 g/cm³; silty clay loam 1.10–1.30 g/cm³; clay 0.95–1.20 g/cm³. The calculator presets use the midpoint of these ranges.

What is management allowed depletion (MAD)?

MAD is the fraction of available water capacity that can be depleted before irrigation is required. A MAD of 50% means you irrigate when half the available water is gone. Common values: 40–50% for vegetables and shallow-rooted crops; 50–60% for field crops; 60–70% for drought-tolerant crops.

How is the irrigation requirement calculated?

Irrigation Depth (inches) = (Field Capacity VWC − Current VWC) × Root Zone Depth (inches). To convert to acre-inches multiply by field area in acres. This represents the net water needed to refill the profile to field capacity, ignoring application efficiency losses.

Soil Moisture Calculator

Name: Soil Moisture Calculator
Availability: InStock
Author: Nham Vu

Enter your soil type, field capacity, wilting point, and current moisture to calculate volumetric water content and irrigation water needed.

Soil & Moisture Parameters

Soil Texture Class

Select a texture class to auto-fill typical FC, PWP, and bulk density values.

FC (%) VWC

PWP (%) VWC

Bulk Density g/cm³

FC = field capacity, PWP = permanent wilting point (both as volumetric %).

Current Soil Moisture

VWC = sensor reading; Gravimetric = oven-dry lab result (requires bulk density).

Effective Root Zone Depth

Depth of soil layer being monitored or managed for irrigation.

Management Allowed Depletion (MAD) %

Fraction of available water that can be depleted before irrigation. Typical range: 40–60%.

Field Area (optional)

Enter area to calculate total volume of irrigation water needed.

Fill in the soil parameters and click Calculate to see moisture status and irrigation needs.

Summary

Enter your soil type, field capacity, wilting point, and current moisture to calculate volumetric water content and irrigation water needed.

How it works

Select your soil texture class or enter a custom bulk density.
Enter or confirm the field capacity (FC) and permanent wilting point (PWP) for that soil.
Input the current soil moisture reading (gravimetric % or volumetric %).
Enter the effective root-zone depth and field area (optional).
Click Calculate to see volumetric water content, available water, deficit, and irrigation requirement.

Use cases

Determine how much irrigation water to apply before the next rain event.
Monitor soil water status and schedule drip or sprinkler irrigation runs.
Convert gravimetric soil moisture lab results to volumetric water content.
Calculate available water capacity between field capacity and wilting point.
Estimate soil water deficit for precision irrigation management.
Compare moisture status across different soil texture zones in a field.
Verify soil probe readings against expected field capacity benchmarks.
Plan cover-crop termination timing based on soil water storage.

Frequently Asked Questions

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Last updated: 2026-05-29 · Reviewed by Nham Vu