Learn: Degree of saturation
Degree of saturation tells you how much of a soil’s void space is filled with water. The remaining void space contains air; the solid grains do not belong in the denominator.
What the formula is saying
Divide water volume Vw by total void volume Vv, then multiply by 100 to express the fraction as a percentage. Full saturation means water fills all voids, not that the entire sample is water.
Read the symbols in plain language
- Vw
- Water volume
Water volume. Only the void volume can be shared between water and air in this calculation.
m³Cubic metres measure volume, or a first moment of area where explicitly identified.
- Vv
- Void volume
Void volume. Only the void volume can be shared between water and air in this calculation.
m³Cubic metres measure volume, or a first moment of area where explicitly identified.
- Sr
- Result to find
Degree of saturation. Multiply the dimensionless fraction by one hundred exactly once.
%
Sort out the units first
Vw and Vv must use the same volume unit, here m³. The ratio is dimensionless and the displayed result is percent. A value of 75 means 75%, not a ratio of 75.
Assumptions before calculating
Use representative volumes or masses from the same soil sample and the same state. Treat solids, water and air as distinct phases; the stated phase relationship does not determine soil strength or suitability for construction.
Let’s solve one together
Read the given values, follow each operation, then check what the result means.
Read the supplied values as one complete study case. Find Sr and explain the result in the stated output unit.
- Vw · Water volume
- 0.3 m³
- Vv · Void volume
- 0.4 m³
Find the water-filled void fraction
Only the void volume can be shared between water and air in this calculation.
(0.3) ÷ (0.4) = 0.75Express saturation as a percentage
Multiply the dimensionless fraction by one hundred exactly once.
(0.75) × 100 = 75 %
Does this worked answer make sense?
No water gives 0%; water volume equal to void volume gives 100%. A result outside 0–100% signals invalid inputs or incompatible measurements.
A second worked example — different values
A second case uses different data. Predict which way the answer will change, then calculate it without reusing the first answer.
- Vw · Water volume
- 0.2 m³
- Vv · Void volume
- 0.25 m³
Find the water-filled void fraction
Only the void volume can be shared between water and air in this calculation.
(0.2) ÷ (0.25) = 0.8Express saturation as a percentage
Multiply the dimensionless fraction by one hundred exactly once.
(0.8) × 100 = 80 %
Now try your own values
Change a value or its unit. The same method will show your calculation, step by step.
Results update only when you calculate. The lesson example above stays unchanged.
Your turn — check your understanding
Solve this separate case yourself. Use only the values below; the two worked examples use different data. Give the requested result in the selected unit.
- Vw · Water volume
- 0.27 m³
- Vv · Void volume
- 0.36 m³
Find: Learn: Degree of saturation
A hint, not the answer
Divide water volume Vw by total void volume Vv, then multiply by 100 to express the fraction as a percentage. Full saturation means water fills all voids, not that the entire sample is water.
Vw and Vv must use the same volume unit, here m³. The ratio is dimensionless and the displayed result is percent. A value of 75 means 75%, not a ratio of 75.
Show the full practice solution
Compare the steps with your work; revealing a solution does not mark the lesson complete.
Find the water-filled void fraction
Only the void volume can be shared between water and air in this calculation.
(0.27) ÷ (0.36) = 0.75Express saturation as a percentage
Multiply the dimensionless fraction by one hundred exactly once.
(0.75) × 100 = 75 %
Avoid the common trap
Do not divide by total soil volume. Do not confuse saturation with porosity or water content by mass, and do not multiply by 100 twice.
When this method applies — and when it does not
Require Vv > 0 and 0 ≤ Vw ≤ Vv. Volumes exceeding the void space are inconsistent with this phase model. Saturation alone does not give pore pressure, drainage rate or water content by mass.
For study and understanding, not approval of a real structure, site operation or design. Apply the correct standard, National Annex and professional review to actual engineering work.
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Sources & further reading
References open in a new tab and explain the underlying principles. The teaching text and examples here are SimpleFlick’s own; the source organisations have not endorsed this calculator.
Reading focus: Degree of saturation. Read the relevant soil phase, seepage, earth-pressure, settlement or foundation topic. Effective stress, drainage and idealized geometry determine whether the relationship applies.
Lesson updated: · Both examples and the separate practice case are checked against an independent high-precision numerical implementation. This verifies arithmetic for the stated model, not engineering certification.