Understanding how quickly water moves through soil is essential for gardeners, farmers, landscapers, and anyone managing irrigation. An infiltration rate calculator is a simple but powerful tool that estimates how fast water enters the soil surface—measured in inches per hour—based on three key soil properties: sand content, clay content, and organic matter (OM%).

Why Infiltration Rate Matters

Infiltration rate affects nearly every aspect of soil and plant health. High infiltration reduces runoff and erosion, improves drought resilience, and ensures nutrients move efficiently into the root zone. Low infiltration can lead to standing water, compaction, reduced oxygen, and nutrient tie-ups.

The Three Variables That Drive Infiltration

1. Sand (%)
Sand particles are large and create wide pore spaces. Soils high in sand typically absorb water quickly. For example, soils with 80–90% sand can commonly show infiltration rates above 3–4 in/hr, depending on their organic matter levels.

2. Clay (%)
Clay particles are extremely small and pack tightly, slowing water entry. Soils with high clay content (40–60% clay) often have infiltration rates below 0.2 in/hr, especially when organic matter is low.

3. Organic Matter (%)
Organic matter improves soil structure, increases aggregation, and creates more stable pore spaces. Even a small change—such as raising OM from 1% to 3%—can significantly increase infiltration, especially in sandy or loamy soils where structure responds quickly to organic inputs.

Disclaimer:

All infiltration rate estimates generated by calculators or lookup tables are approximate and should not be used as a substitute for professional soil testing. Actual field infiltration can vary based on compaction, moisture, management history, and site conditions. For precise recommendations, consider a laboratory analysis or on-site infiltration test.