Measure how quickly water enters the soil surface.
Use a USDA-style single ring or enter a known ring diameter and water depth. Time repeated trials, preserve site conditions, and report the arithmetic without turning one field test into a soil diagnosis.
What the calculation does
Rate = target water depth ÷ elapsed time × 3,600 seconds per hour.
The USDA presets use the source-specified 444 mL or 107 mL water volume as an approximately one-inch test. Custom mode calculates the required circular water volume from the entered inner diameter and target depth.
The average is the arithmetic mean of recorded trial rates. The last-two difference is descriptive only; it is not a pass/fail threshold.
If 25.4 mm of water enters in 3,600 seconds, the calculated rate is 25.4 mm/h, equal to 1.00 in/h.
No soil rating, correction factor, or recommendation is added.
One location cannot represent every condition.
- Initial dry-soil behavior can differ from later trials; repeat the test and retain trial order.
- A single ring permits lateral flow. Large cracks, shrink–swell soils, hydrophobic surfaces, ring leakage, disturbance, and recent wetting can materially affect the result.
- Test more than one representative location when spatial variability matters.
- Formal stormwater, engineering, construction, or regulatory decisions may require a different method and a qualified local professional.
Protocol and scope
USDA NRCS Soil Health — Infiltration test guide provides the 3-inch and 6-inch single-ring field procedure and repeat-until-steady guidance.
Oregon State University Extension — Infiltration Testing for Low Impact Development explains why formal site assessment may require different test geometry and procedures.
FAO — Measurement of infiltration describes changing initial and basic infiltration behavior and ring-method limitations.