Soil Infiltration Rate Calculator
Calculate water infiltration rate from the fall in ponded water level over a measured time interval.
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Measured infiltration rate for this interval
A measured infiltration rate does not uniquely identify soil texture and should not be used by itself to assign groundwater recharge potential.
Reference Ranges
| Measured rate | Typical FAO texture comparison |
|---|---|
| ≥30 mm/hr | Sand |
| 20–<30 mm/hr | Sandy loam |
| 10–<20 mm/hr | Loam |
| 5–<10 mm/hr | Clay loam |
| 1–<5 mm/hr | Clay |
These are comparison ranges, not a laboratory soil-texture determination.
How to Use
Measure the water level in the inner ring at the start and end of a timed interval. If water is added during the interval, enter that added amount as an equivalent depth in millimetres.
The calculator uses: infiltrated depth = initial level + water added − final level, then converts that depth to mm/hr.
For a representative basic or steady infiltration rate, continue measurements until the rate becomes approximately constant. A double-ring infiltrometer is preferred because the outer ring reduces lateral flow from the inner ring.
Method: Infiltration rate is the depth of water entering the soil per unit time. This calculator is appropriate for ring-infiltrometer intervals where changes in ponded water depth represent infiltrated depth.
Interpretation: FAO gives broad infiltration classes of <15 mm/hr (low), 15–50 mm/hr (medium), and >50 mm/hr (high). Soil texture, antecedent moisture, structure, compaction and other conditions all affect measured infiltration.
Important: The original approach of assigning “Clay / Silt / Sand” and “Poor / Good / Excellent recharge” directly from one infiltration-rate value is not technically defensible. Recharge depends on additional hydrogeologic factors.
References: FAO — Infiltration Rate and Infiltration Test · FAO — Soil and Water