Void Ratio Calculator

Void ratio e is defined as the volume of voids divided by the volume of solids: e = Vv ÷ Vs.

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Enter Values

Volume of voids Vv (cm³ or any unit)

Volume of solids Vs (same unit as Vv)

Porosity n (%) — use instead of volumes

Enter your values and press Calculate to see results.

Before you rely on this: First-pass guide only. Verify safety-critical or regulated work against the relevant standards, your project requirements and a qualified professional.

How to use this calculator

Enter BOTH the volume of voids (Vv) and the volume of solids (Vs) in any consistent unit — the ratio is dimensionless, so cm³, mm³ or in³ all work as long as both use the same unit.
Or, if you already know porosity, leave the volumes blank and enter porosity n (%) — the tool converts it to void ratio via e = n ÷ (1 − n).
Read the void ratio (e), the equivalent porosity (n%), and the specific volume (1 + e) from the results, then expand the working to see each step.

How it works

Void ratio e is defined as the volume of voids divided by the volume of solids: e = Vv ÷ Vs. Unlike porosity, the denominator is the solid volume only (not the total volume), which is why e can exceed 1 in loose or organic soils. This tool computes e directly from the two volumes when you supply them.

Void ratio and porosity describe the same pore space from different reference volumes and convert exactly: e = n ÷ (1 − n) and n = e ÷ (1 + e), where n is the decimal porosity. The specific volume (total volume per unit solid volume) is simply 1 + e. When you enter porosity instead of volumes, the tool applies e = n ÷ (1 − n); otherwise it uses the volumes directly.

Worked example

Void ratio from voids and solids volumes. A soil specimen has 30 cm³ of voids (pore space) and 70 cm³ of solid grains. Enter Vv = 30 and Vs = 70. Void ratio e = 30 ÷ 70 = 0.4286. This converts to a porosity n = e ÷ (1 + e) = 0.4286 ÷ 1.4286 = 30.00%, and a specific volume of 1 + e = 1.4286.

Common mistakes

Confusing void ratio with porosity. Void ratio divides voids by SOLIDS (e = Vv/Vs), while porosity divides voids by TOTAL volume (n = Vv/V). They are related but not equal — e = 0.43 corresponds to n = 30%, not 43%.
Using the total sample volume as the solid volume. Vs is the volume of grains only; subtract the void (pore) volume from the total before entering Vs, or use the porosity input instead.
Entering porosity as a decimal (0.30) when the field expects a percentage (30). A porosity of 100% or more is physically impossible and will be rejected.

Frequently asked questions

What is the difference between void ratio and porosity?

Void ratio e = volume of voids ÷ volume of solids, so its reference is the solid grains only and it can be greater than 1. Porosity n = volume of voids ÷ total volume, so it is always between 0 and 1 (0–100%). They convert exactly with e = n ÷ (1 − n) and n = e ÷ (1 + e).

Can void ratio be greater than 1?

Yes. Because the denominator is the solid volume, loose sands, soft clays and organic soils commonly have void ratios above 1 (the pore volume exceeds the solid volume). Dense, well-graded granular soils typically sit around 0.3–0.7.

Do the volume units matter?

No — void ratio is dimensionless, so any consistent unit works for both Vv and Vs (cm³, mm³, m³, in³). Just make sure both volumes use the same unit.

Does this calculator need specific gravity or water content?

Not for void ratio itself, which is purely a volume ratio. Specific gravity, dry density and water content come into phase-relationship calculations (e.g. deriving e from dry unit weight); this tool focuses on the core e = Vv/Vs definition and the exact porosity conversion.

Tip: Enter any known values to calculate the remaining results.

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