What is void ratio and why does it matter?

Void ratio (e) is the ratio of the volume of voids to the volume of solids in a soil. A lower void ratio means denser packing. It directly controls permeability, compressibility, and shear strength — three properties central to foundation and slope design.

What is the typical void ratio range for sands and clays?

Loose sands typically have e ≈ 0.6–1.0; dense sands are around 0.3–0.6. Soft clays can reach e = 1.5–3.0, and highly plastic clays can exceed e = 5.0. The critical state void ratio separates contractive from dilative behavior.

How is void ratio related to porosity?

Porosity (n) is the ratio of void volume to total volume, so n = e / (1 + e). Void ratio is unbounded above 0, while porosity is bounded 0–1. Both describe the same pore space — porosity is easier to visualize, void ratio is more convenient for calculations.

What does degree of saturation mean?

Degree of saturation (S) is the fraction of the void space filled with water. S = 0 means completely dry, S = 1 (or 100%) means fully saturated. Most natural soils above the water table have S between 0.5 and 0.95.

What specific gravity value should I use?

For most mineral soils, Gs is between 2.60 and 2.80. Quartz-rich sands are near 2.65, clays around 2.70–2.75, and organic soils can be as low as 2.00. When no lab data is available, Gs = 2.70 is a reasonable default.

Which unit systems are supported?

The calculator supports both SI (kN/m³, kPa) and US Customary (pcf — pounds per cubic foot). Switch between them using the unit selector; inputs and outputs convert automatically.

Void Ratio Calculator

Enter soil index properties to instantly compute void ratio, porosity, degree of saturation, and dry unit weight.

Soil Index Properties

Unit System

Specific Gravity of Solids, G_s (dimensionless)

Typical range: 2.60–2.80 for mineral soils

Water Content, w (%)

Mass of water / mass of dry solids × 100

Bulk Unit Weight, γ (kN/m³)

Typical range: 15–22 kN/m³

Computed Results

Void Ratio

— e

Porosity

— n (%)

n = e / (1 + e)

Degree of Saturation

— S (%)

S = w · Gs / e

Dry Unit Weight

— kN/m³

γd = γ / (1 + w)

Relationships Used

γd = γ / (1 + w/100)

e = (Gs · γw / γd) − 1

n = e / (1 + e)

S = (w/100 · Gs) / e

γw = 9.81 kN/m³ (SI) or 62.4 pcf (US)

Summary

The Void Ratio Calculator computes the four fundamental soil index properties — void ratio (e), porosity (n), degree of saturation (S), and dry unit weight (γd) — from specific gravity, water content, and bulk unit weight. These parameters appear in virtually every geotechnical analysis, from consolidation settlement to liquefaction assessment. The calculator supports both SI (kN/m³) and US Customary (pcf) unit systems and updates results in real time.

How it works

Enter the specific gravity of soil solids (Gs), typically 2.60–2.80 for most soils.
Provide the natural water content (w%) of the soil sample.
Input the bulk unit weight (γ) in kN/m³ or pcf.
Select your preferred unit system (SI or US Customary).
Results update instantly: void ratio (e), porosity (n), degree of saturation (S), and dry unit weight (γd).

Use cases

Classify soil compaction state and density in geotechnical site investigations.
Check whether a soil sample is loose, medium dense, or dense based on void ratio.
Calculate degree of saturation to assess drainage and pore pressure conditions.
Determine dry unit weight for compaction control and earthwork design.
Support laboratory report preparation from standard index property tests.
Verify hand calculations from ASTM D7263 or AASHTO T99 test procedures.

Frequently Asked Questions

Last updated: 2026-06-18 · Reviewed by Nham Vu