How to calculate soil void ratio
A soil sample contains solid particles and spaces between them. Void ratio compares the total space volume, whether occupied by water or air, with the volume of solids.
What the formula is saying
Use e = Vv/Vs. The reference volume is the solids only. Because void volume can exceed solid volume, e is not necessarily below 1.
Read the symbols in plain language
- Vv
- Void volumem³
- Vs
- Solids volumem³
Sort out the units first
Use the same volume unit on both sides. 0.3 m³ of voids and 0.6 m³ of solids form a total volume of 0.9 m³.
Let’s solve one together
Read the given values, follow each operation, then check what the result means.
- Vv · Void volume
- 0.3 m³
- Vs · Solids volume
- 0.6 m³
Count all void volume
Include both air-filled and water-filled spaces.
(0.3) = 0.3 m³Compare with solids only
Use Vs, not the total sample volume.
(0.3) ÷ (0.6) = 0.5
Does this worked answer make sense?
e = 0.5 means half a unit of voids for every unit of solids. It does not mean half the total volume is voids.
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
Use these new values. Work it out first, then check your answer.
- Vv · Void volume
- 0.4 m³
- Vs · Solids volume
- 0.5 m³
Find: soil void ratio
A hint, not the answer
Use e = Vv/Vs. The reference volume is the solids only. Because void volume can exceed solid volume, e is not necessarily below 1.
Use the same volume unit on both sides. 0.3 m³ of voids and 0.6 m³ of solids form a total volume of 0.9 m³.
Show the full practice solution
Compare the steps with your work; revealing a solution does not mark the lesson complete.
Count all void volume
Include both air-filled and water-filled spaces.
(0.4) = 0.4 m³Compare with solids only
Use Vs, not the total sample volume.
(0.4) ÷ (0.5) = 0.8
Avoid the common trap
Using total volume in the denominator produces porosity, not void ratio. Air volume alone is not total void volume.
When this method applies — and when it does not
Phase-volume definition. It does not by itself determine bearing capacity, compressibility or drainage behaviour.
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.
One idea understood. Keep going.
This optional checkmark is saved only in this browser. It is your own progress note, not a certificate.
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.
Lesson updated: · Worked examples checked against the implemented formula; not an independent engineering certification.