Soil Infiltration Rate Calculator
Water for 1 inch: 463 mL. NRCS’s kit uses 107 mL for a 3-inch ring or 444 mL for a 6-inch ring.
The second inch gives the steady rate. Run the test twice in a row and use the slower, second soak.
Optional. Loads the soil USDA maps at a US address to prefill and tailor the result.
The steps
- Clear residue off a flat spot and drive a 3- or 6-inch ring 3 inches into the soil.
- Line the ring with plastic wrap and pour in 107 mL (3-inch ring) or 444 mL (6-inch ring) of water, which is 1 inch.
- Pull the wrap away so the water hits the soil at once, and time how long until the soil just glistens.
- Repeat the pour straight away and time the second inch for the steady rate[1].
Typical infiltration rates
These are steady-state rates (Hillel 1982), reached once the soil below the ring is wet through[1].
| Soil | Steady rate (in/hr) |
|---|---|
| sand | >0.8 |
| sandy and silty soils | 0.4–0.8 |
| loam | 0.2–0.4 |
| clayey soils | 0.04–0.2 |
| sodic clayey soils | <0.04 |
Worked example
If the first inch soaks in in 60 minutes and the second in 120 minutes, the steady rate is 60 ÷ 120 = 0.5 in/hr, or 12.7 mm/hr (calculated[2]), which falls in the sandy and silty soils band[1].
Test more than one spot
The USDA 6-inch-ring method is simple, but it varies a lot between tries and is not an accurate estimate of infiltration potential on its own[3]. Repeat it in several spots across the area and compare the rates rather than trusting one reading.
Infiltration is not the same as drainage
This test measures how fast water enters the surface[1]. A percolation (perk) test times how fast water drains out of a hole dug into the soil[4]. For that side of the question, see improving soil drainage and its perk test.
How this calculator works
The rate is 60 ÷ the minutes the second inch took, in inches per hour[1]. NRCS’s kit pours 107 mL into its 3-inch ring and 444 mL into its 6-inch ring[1]. For a ring of any other size, the calculator works out one inch of water as π r² × 1 inch, in milliliters (calculated[2]), so its figure for a nominal ring can differ a little from the kit’s.
With “Use my soil”, the mapped saturated conductivity (Ksat) class is shown as context, not as the infiltration rate, since Ksat describes water moving through soil that is already saturated[5]. USDA sorts Ksat into six classes, from very low to very high[5].
Frequently asked questions
What is a good infiltration rate?
There is no single number. A loam runs about 0.2 to 0.4 in/hr, sand over 0.8, and clay 0.04 to 0.2. What matters is that water soaks in before it ponds[1].
How much water do I use for an infiltration test?
One inch of water over the ring: 107 mL for a 3-inch ring or 444 mL for a 6-inch ring in NRCS’s kit, and the calculator computes it for any diameter[1].
Sources
- USDA NRCS Soil Health Guide, Infiltration
- NIST, Guide for the Use of the International System of Units (SP 811), Appendix B.8: Factors for Units Listed Alphabetically
- Journal of Soil and Water Conservation (2022), Comparison of Infiltration Test Methods for Soil Health Assessment
- University of Kentucky Extension, ID-237 Soil Percolation: A Key to Survival of Landscape Plants (2016)
- USDA NRCS, Soil Survey Manual (Agriculture Handbook 18), Ch. 3: saturated hydraulic conductivity classes
Marko Visic · MPharm, BSc Physics · Last reviewed November 13, 2026