Rock Density and Porosity Calculator
Calculate bulk density, grain (matrix) density, fluid density, and porosity using standard petrophysical relationships. Provide any three known values to solve for the fourth.
Measured density of the rock sample (solid + pore fluid)
Density of the solid mineral grains (quartz ≈ 2.65, calcite ≈ 2.71, dolomite ≈ 2.87)
Density of pore-filling fluid (water ≈ 1.00, oil ≈ 0.80, gas ≈ 0.001–0.3)
Fraction of rock volume occupied by pores (0–100%)
⚠️ Leave exactly one field blank — it will be calculated from the other three.
Formula
The fundamental petrophysical relationship linking bulk density, grain density, fluid density, and porosity:
ρb = φ · ρf + (1 − φ) · ρg
Rearranged to solve for each unknown:
- Grain density: ρg = (ρb − φ · ρf) / (1 − φ)
- Fluid density: ρf = (ρb − (1 − φ) · ρg) / φ
- Porosity: φ = (ρg − ρb) / (ρg − ρf)
- Void ratio: e = φ / (1 − φ)
Where: ρb = bulk density, ρg = grain (matrix) density, ρf = pore fluid density, φ = porosity (fraction).
Assumptions & References
- References: Archie (1942), AAPG Bulletin; Schlumberger Log Interpretation Principles (1989); Tiab & Donaldson, Petrophysics (4th ed., 2015).