Void Ratio and Porosity (e = n/(1 − n))
Worked example: n = 40% → e = 0.6667 — press Try an example to run it live, then adjust anything.
Enter your known values, leave one input blank, and solves for the missing one. Tap a variable’s symbol to see what it means, with a typical value. Try different units for next level excitement!
Void Ratio and Porosity (e = n/(1 − n)) explained
Both numbers describe the same emptiness, and both are needed because they have different denominators. Void ratio e divides void volume by the volume of solids, which stays constant as a soil compresses — that is why consolidation theory is written in e. Porosity n divides void volume by the total volume, which is what you measure with a sampling tube, so seepage and storage calculations use n. A porosity of 0.40 corresponds to e = 0.40 ÷ 0.60 = 0.667; a void ratio of 0.85 corresponds to n = 0.85 ÷ 1.85 = 0.459.
The trap is the ceiling: porosity can never reach 1 and is typically 0.25–0.50 in sands and 0.40–0.70 in clays, while void ratio has no upper bound at all — a soft marine clay can sit at e = 3 and a Mexico City lacustrine clay at e = 7, meaning seven parts water to one part solid. That is not a typo, it is why the Palacio de Bellas Artes has sunk several metres into the Valley of Mexico since 1904 while the streets around it sank further still. If a "porosity" you have been handed is greater than 1, someone has given you a void ratio.
Void Ratio and Porosity (e = n/(1 − n)) formula
- = Void ratio
- = Porosity
Missing one of these? Work it out first, then come back
- Void ratio — Degree of Saturation (Se = wGs), Saturated Unit Weight
- Porosity — Seepage Velocity from Discharge Velocity