Soil & Water Quality Calculators
Work out how much water your soil can hold and release, how fast water soaks in, what texture you're dealing with, and whether salts or sodium are building up in your soil or irrigation water. Each calculator answers one question, shows its formula, and works in US or metric units.
Which soil calculator do you need?
Find your question below. Each calculator does one job, so picking the right one gets you a precise answer.
| Your question | Use this calculator | How it works |
|---|---|---|
| How much water can my soil hold and give back to plants? | Available Water Capacity Calculator | AWC per inch by texture, or field capacity minus wilting point, times root depth. |
| How much can the soil dry out before I need to irrigate? | Management Allowed Depletion Calculator | Total available water times a depletion percentage (FAO p value) by crop. |
| How deep do my plant's roots actually draw water from? | Root Zone Depth Calculator | Plant type and age, plus soil restrictions, set the depth to wet. |
| How deep will an inch of applied water actually reach? | Wetting Front Depth Calculator | Applied depth over the soil's deficit per inch, or run it in reverse. |
| How fast does water soak into my soil? | Soil Infiltration Rate Calculator | Ring or can test readings over time, compared with your sprinkler rate. |
| How wet is my soil right now? | Soil Moisture Calculator | Wet and dry sample weights and bulk density give moisture and water depth. |
| What type of soil do I have — sand, loam or clay? | Soil Texture Calculator | Sand, silt and clay percentages, or jar-test layers, to a USDA class. |
| How much extra water do I need to flush salts below the roots? | Leaching Requirement Calculator | Water and soil salinity (FAO-29) give the leaching fraction and adjusted depth. |
| Is my water or soil too high in sodium? | Sodium Adsorption Ratio Calculator | Sodium, calcium and magnesium levels, converted to meq/L, combine into SAR. |
| Is my irrigation water safe to use long-term? | Irrigation Water Quality Calculator | Lab report values checked against FAO-29 restriction thresholds, parameter by parameter. |
All soil & water quality calculators
Water storage and root zone
- Available Water Capacity CalculatorTotal available water in the root zone, layer by layer
- Management Allowed Depletion CalculatorReadily available water depth before you should irrigate
- Root Zone Depth CalculatorEffective root depth to plan how deep to wet
- Wetting Front Depth CalculatorHow deep applied water penetrates, or the reverse
Testing and identifying your soil
Soil & water quality basics
What extension and FAO research says, in brief. Each calculator page goes into detail and cites its sources.
Water capacity rises with clay content
University of California Agriculture and Natural Resources guidance puts available water capacity at about 0.5 to 1.0 inch per foot of depth for sandy soils, 1.0 to 2.0 inches per foot for loams, and up to 2.5 inches per foot for clay. Multiplying by root depth gives the total available water.
Infiltration slows as soils get finer
USDA Natural Resources Conservation Service steady-state testing puts sandy soils above 0.8 inch per hour, loams around 0.2 to 0.4 inch per hour, and clayey soils down to 0.04 to 0.2 inch per hour, with sodic clay soils slower still.
Texture sorts into 12 standard classes
The USDA groups soils into 12 textural classes, from sand to clay, based on the share of sand, silt and clay found by a lab particle-size test or a jar test at home.
Leaching keeps salts from building up
FAO Irrigation and Drainage Paper 29 (Ayers and Westcot) gives the leaching requirement as LR = ECw ÷ (5 × ECe − ECw), where ECw is the irrigation water's salinity and ECe is the crop's soil-salinity threshold.
Water quality thresholds and local discharge or drainage rules always come first; a calculator here is a planning estimate, not a substitute for a lab report or a permit. For the data behind the infiltration figures, see the soil infiltration rate chart.
Related calculator categories
- Scheduling and ET calculatorsSoil water balance, effective rainfall and water budgets
- Agriculture calculatorsCrop water requirements that build on your soil data
- Sprinkler calculatorsPrecipitation rates to compare against infiltration
- Garden and tree calculatorsBeds, vegetables, containers, trees and shrubs
- Fertigation calculatorsInjection rates once your water quality is known
- All calculatorsEvery irrigation calculator by category
Sources and review
This page and its calculators are reviewed by Daniel Reeves, PE, CID. Last reviewed . See our methodology and editorial policy, or report an error.
- University of California Agriculture and Natural Resources. Soil Texture.
- USDA Natural Resources Conservation Service. Soil Infiltration (Soil Health Guides for Educators).
- USDA Natural Resources Conservation Service. National Soil Survey Handbook, soil texture classification (12 USDA textural classes). [VERIFY URL]
- Ayers, R. S. and Westcot, D. W. (1985, rev. 1989). Water Quality for Agriculture. FAO Irrigation and Drainage Paper 29.