Soil Moisture Calculator
Enter the wet and dry weights of a soil sample to get its moisture content (gravimetric %), add the core volume or bulk density for volumetric %, then see available water, depletion and how much irrigation refills the root zone.
Soil moisture content (gravimetric) = (wet weight − dry weight) ÷ dry weight × 100, and volumetric water content = gravimetric content × bulk density ÷ density of water (1 g/cm³).
Use the Soil Moisture Calculator
1. Moisture content from a soil sample
Gravimetric method: weigh the moist sample, oven-dry it until its weight stops changing, and weigh it again. Use the same unit (grams) for every weight.
- Moisture content (dry basis)
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- Volumetric water content
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- Bulk density
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- Moisture (wet basis)
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- Porosity
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- Degree of saturation
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- Water held
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- Water in sample
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2. Root-zone water and irrigation deficit
Soil & Moisture Parameters
Fills rule-of-thumb FC, PWP and bulk density; FC − PWP matches the NRCS typical available water for that texture. Use lab or Web Soil Survey values when you have them.
FC = field capacity, PWP = permanent wilting point (both as volumetric %).
VWC = sensor reading; Gravimetric = oven-dry lab result (requires bulk density).
Depth of soil layer being monitored or managed for irrigation.
Fraction of available water that can be depleted before irrigation. Typical range: 40–60%.
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.
Soil Moisture Status
Key Moisture Metrics
AWC = available water capacity; Deficit = inches of water needed to reach FC.
Irrigation Water Requirement
Net depth to refill profile from current moisture to field capacity.
Total Irrigation Volume
Calculation Breakdown
Available water capacity by soil texture (USDA NRCS)
From the NRCS National Engineering Handbook Part 652 (Irrigation Guide), Table 2-1. Available water is held between field capacity (1/10 bar for sandy soils, 1/3 bar for finer soils) and the permanent wilting point (15 bar). Rock fragments, salinity and compaction lower these values; use Web Soil Survey data for a specific field.
| Texture | AWC range (in/in) | AWC range (in/ft) | Typical (in/ft) |
|---|---|---|---|
| Coarse sand | .01–.03 | 0.1–0.4 | 0.25 |
| Sand | .01–.03 | 0.1–0.4 | 0.25 |
| Fine sand | .05–.07 | 0.6–0.8 | 0.75 |
| Very fine sand | .05–.07 | 0.6–0.8 | 0.75 |
| Loamy coarse sand | .06–.08 | 0.7–1.0 | 0.85 |
| Loamy sand | .06–.08 | 0.7–1.0 | 0.85 |
| Loamy fine sand | .09–.11 | 1.1–1.3 | 1.25 |
| Loamy very fine sand | .10–.12 | 1.0–1.4 | 1.25 |
| Coarse sandy loam | .10–.12 | 1.2–1.4 | 1.3 |
| Sandy loam | .11–.13 | 1.3–1.6 | 1.45 |
| Fine sandy loam | .13–.15 | 1.6–1.8 | 1.7 |
| Very fine sandy loam | .15–.17 | 1.8–2.0 | 1.9 |
| Loam | .16–.18 | 1.9–2.2 | 2.0 |
| Silt loam | .19–.21 | 2.3–2.5 | 2.4 |
| Silt | .16–.18 | 1.9–2.2 | 2.0 |
| Sandy clay loam | .14–.16 | 1.7–1.9 | 1.8 |
| Clay loam | .19–.21 | 2.3–2.5 | 2.4 |
| Silty clay loam | .19–.21 | 2.3–2.5 | 2.4 |
| Sandy clay | .15–.17 | 1.8–2.0 | 1.9 |
| Silty clay | .15–.17 | 1.8–2.0 | 1.9 |
| Clay | .14–.16 | 1.7–1.9 | 1.8 |
Quick answer
Weigh a fresh soil sample, oven-dry it and weigh it again. The water lost divided by the dry soil weight is the gravimetric moisture content θg. If the sample came from a core of known volume, bulk density ρb = dry weight ÷ core volume, and the volumetric water content is θv = θg × ρb ÷ ρw, the form soil moisture sensors report and irrigation uses: θv × root depth = depth of water in the soil. Plant-available water is the part between field capacity and the permanent wilting point; USDA NRCS lists typical available water capacity from 0.01–0.03 in/in for sand to 0.19–0.21 in/in for silt loam and clay loam.
Examples
| Sample | Working | Result |
|---|---|---|
| Wet 100 g, dry 80 g | (100 − 80) ÷ 80 | θg = 25% |
| Same, 70 cm³ core | ρb = 80 ÷ 70 = 1.143 g/cm³ | θv = 25% × 1.143 = 28.6% |
| θg 20%, ρb 1.35 g/cm³ | 0.20 × 1.35 | θv = 27% |
| θv 27%, 24 in root zone | 0.27 × 24 | 6.48 in of water held |
| FC 28%, now 20%, 24 in | (0.28 − 0.20) × 24 | 1.92 in to refill |
Enter your sample weights above to get the moisture content, then your soil and root depth for the irrigation deficit.
Summary
This soil moisture calculator works in two steps. First, the gravimetric method: enter the wet and oven-dry weights of a sample (and the container weight if you weighed it in a tin) to get the moisture content on a dry-weight basis, plus the wet-basis value. Add the core volume to get bulk density, volumetric water content, porosity, degree of saturation and inches of water per foot. Second, the irrigation check: with field capacity, wilting point and root depth it computes available water capacity, how much of it is used, the management allowed depletion (MAD) threshold and the net irrigation depth and volume to refill the profile. A USDA NRCS table of available water capacity by soil texture is included for reference.
How it works
- Weigh the moist soil sample, oven-dry it and weigh it again; enter both weights and the container (tare) weight if any.
- Optionally enter the volume of the sampling core to get bulk density and volumetric water content.
- Click "Use as current moisture" to carry the result into the irrigation section.
- Select a soil texture or type your own field capacity, wilting point and bulk density, then enter the root-zone depth and MAD.
- Read the moisture status, available water, depletion and the inches (or mm) and gallons of irrigation needed to reach field capacity.
Use cases
- Calculating the moisture content of a soil or sand sample from lab weights.
- Converting gravimetric moisture to volumetric water content for irrigation scheduling.
- Checking soil moisture sensor readings against an oven-dry sample.
- Finding how many inches of water to apply to refill the root zone to field capacity.
- Estimating available water capacity from soil texture with NRCS values.
- Teaching soil physics: bulk density, porosity and degree of saturation.