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Use our porosity to void ratio calculator to convert porosity into void ratio. Learn the formula, steps, relationship, and calculation with an example.
| Equation | Purpose | Notes |
|---|---|---|
| e = n ÷ (1 − n) | Void ratio from porosity (decimal) | n = Vᵥ÷V |
| e = P ÷ (100 − P) | Void ratio from porosity (percent) | P = porosity % |
| n = e ÷ (1 + e) | Porosity (decimal) from void ratio | e = Vᵥ÷Vₛ |
| P = [e ÷ (1 + e)] × 100 | Porosity (percent) from void ratio | — |
The porosity to void ratio calculator helps you convert soil porosity into void ratio in seconds. You can enter porosity as a percentage or as a decimal value. The calculator then gives the matching void ratio.
Porosity and void ratio both describe the empty space in soil. But they use different reference volumes. Porosity compares void volume with total soil volume. Void ratio compares void volume with solid volume.
This makes the porosity to void ratio formula useful in soil mechanics, geotechnical engineering, and civil engineering work.
The main equation for void ratio from porosity is:
e = n / (1 − n)
Here, e is the void ratio and n is porosity as a decimal.
If porosity is given as a percentage, use:
e = P / (100 − P)
Here, P is porosity in percent.
For example, if soil porosity is 40%, first use the percentage formula:
e = 40 / (100 − 40)
e = 40 / 60
e = 0.6667
So, a porosity of 40% gives a void ratio of about 0.6667.
The relationship between porosity and void ratio comes from their basic definitions. Porosity is the ratio of void volume to total volume. Void ratio is the ratio of void volume to solid volume.
The main relationship is:
e = n / (1 − n)
The reverse formula for void ratio to porosity is:
n = e / (1 + e)
To express porosity as a percentage:
P = [e / (1 + e)] × 100
Porosity and void ratio are related, but they aren't the same value. Porosity is usually written as a decimal or percentage. Void ratio is a ratio and has no unit.
For the same soil, a 40% porosity does not mean a 0.40 void ratio. Instead:
e = 0.40 / (1 − 0.40) = 0.6667
This is the key difference between void ratio and porosity.
Porosity is also closely related to void fraction. In many contexts, void fraction means the fraction of total volume occupied by voids. In soil mechanics, porosity is commonly used for this purpose.
You can also use the reverse void ratio to porosity calculation when you already know the void ratio.
Suppose a soil sample has a porosity of 35%.
Use:
e = P / (100 − P)
Insert the value:
e = 35 / (100 − 35)
e = 35 / 65
e = 0.5385
Therefore, the void ratio is 0.5385.
The same result can be checked with decimal porosity:
n = 35 / 100 = 0.35
e = 0.35 / (1 − 0.35)
e = 0.35 / 0.65
e = 0.5385
Both methods give the same answer.
The porosity to void ratio calculator makes this conversion quick and easy. The key formula is e = n / (1 − n). When porosity is given as a percentage, use e = P / (100 − P).
For the reverse calculation, use n = e / (1 + e). These simple equations show the direct relationship between porosity and void ratio.
The formula is e = n / (1 − n), where n is porosity as a decimal.
Convert percentage porosity to a decimal, then use e = n / (1 − n). You can also use e = P / (100 − P) when P is in percent.
The formula is n = e / (1 + e). Multiply the result by 100 to get percentage porosity.
Porosity compares void volume with total volume. Void ratio compares void volume with solid volume. They are related but use different reference volumes.
Porosity and void fraction both describe the fraction of total volume occupied by voids. In soil mechanics, porosity is the standard term.
No. Void ratio is dimensionless because it is a ratio of two volumes.