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Rispri LabsENGINEERING A CIRCULAR FUTURE

Free tool · Water conservation

Infiltration Rate Calculator (Double Ring Infiltrometer Test)

Infiltration rate is the drop in water level in the inner ring divided by the time interval, converted to mm/h. The rate falls as the soil wets up; the steady value at the end of the test is the design infiltration rate.

Your inputs

Results update as you type. Example values are filled in.

Test readings

One row per reading. Record the drop in the inner ring since the last reading (refill counts as a fresh start).

#Interval (min)Drop in inner ring (cm)Remove

How to use this calculator

  1. Drive both rings about 10 to 15 cm into the soil and fill both, keeping the outer ring level similar to the inner.
  2. Record the drop in the inner ring over each interval, starting with short intervals.
  3. Enter each interval and drop. Add rows until the last readings stop changing.
  4. Use the steady rate for recharge pit, soak pit or drainage design.

How is infiltration rate calculated from a double ring test?

f (mm/h) = Δh (cm) × 10 × 60 ÷ Δt (min)

Only the inner ring reading is used; the outer ring stops water spreading sideways. The test follows ASTM D3385 and IS 11131. Permeability classes follow the USDA Soil Survey Manual.

Worked example

With :

Steady infiltration rate: 20 mm/h

The calculator also gives rate in cm/h 2 cm/h; rate in m/day 0.48 m/day; rate in inches/h 0.79 in/h.

Assumptions and limits

  • Steady rate is the mean of the last two readings.
  • Field rates vary across a site; test at several points and use a lower value for design.
  • Wet season or compacted soils infiltrate more slowly than the test day may show.

Frequently asked questions

What is a good infiltration rate for a recharge pit?

Moderate or faster soils, above about 15 mm/h, generally suit recharge and soak pits. Slower soils need a larger pit area or a recharge shaft or bore that reaches a permeable layer.

How long does a double ring infiltrometer test take?

Usually 2 to 6 hours. Keep reading until the rate is steady for at least two to three intervals.

What is the difference between infiltration and percolation tests?

Infiltration measures water entering the soil surface from rings. A percolation test measures how fast water drains from a dug hole and is used for septic soak pits.

References

  • ASTM D3385, Standard Test Method for Infiltration Rate of Soils in Field Using Double-Ring Infiltrometer
  • BIS IS 11131:1984, Method of test for determination of infiltration rate of soils
  • USDA, Soil Survey Manual, permeability classes

Built and maintained by the Rispri Labs engineering team. Last updated .