Infiltration Rate Calculator
Free Infiltration rate Calculator for hydrology & water resources. Enter variables to compute results with formulas and detailed steps.
Formula
Rate = V / (A x t)
The infiltration rate formula Rate = V / (A x t) calculates how fast water enters the soil. V is the volume of water (mL) that infiltrated during the test, A is the inner ring area (m²) of the infiltrometer, and t is the elapsed time (minutes). The result, expressed in mL/m²/min, can be converted to mm/hr by multiplying by 0.06. A higher rate indicates more permeable soil, which supports greater groundwater recharge and reduces surface runoff in stormwater design.
Frequently Asked Questions
What is infiltration rate and how is it different from infiltration capacity?
Infiltration rate is the actual volume of water entering the soil per unit area per unit time (mm/hr or mL/m²/min), measured directly in the field. Infiltration capacity is the maximum rate the soil can absorb water under ponded conditions. When rainfall intensity exceeds capacity, water ponds and runoff begins. Infiltration Rate Calculator computes actual rate from volume, area, and time measurements.
How does the formula Rate = V / (A × t) work in a ring infiltrometer test?
V is the volume of water (mL) that infiltrated, A is the inner ring area (m²), and t is the measurement time interval (minutes or seconds). The result gives volume flux per unit area. To convert mL/m²/min to mm/hr, multiply by 0.001 (mL → L), then by 1000 (L/m² = mm), then by 60 (per hr): Rate (mm/hr) = [V(mL) / (A(m²) × t(min))] × 0.06.
How is the steady-state infiltration rate used in Green Infrastructure design?
Rain gardens, bioretention cells, and infiltration basins are designed so overflow occurs only when rainfall intensity exceeds soil infiltration rate. Measured fc values from infiltrometer tests set the design drawdown rate. Typical bioretention media targets fc > 25 mm/hr. Regulatory guidelines (e.g., EPA, local stormwater manuals) require site-specific infiltration testing before facility sizing.
What factors reduce infiltration rate over time during a test?
Soil pore spaces fill with water, reducing capillary suction. Fine particles migrate and clog pores (surface sealing). Air trapped in pores resists downward movement. Swelling of clay minerals closes pathways. For these reasons, rates always decline from f0 toward fc during the first 30–120 minutes of a test. Running the test to steady state is essential for design purposes.
How accurate are the results from Infiltration Rate Calculator?
All calculations use established mathematical formulas and are performed with high-precision arithmetic. Results are accurate to the precision shown. For critical decisions in finance, medicine, or engineering, always verify results with a qualified professional.
How do I get the most accurate result?
Enter values as precisely as possible using the correct units for each field. Check that you have selected the right unit (e.g. kilograms vs pounds, meters vs feet) before calculating. Rounding inputs early can reduce output precision.