Bulk Density to Porosity Calculator
Enter soil bulk density and particle density to compute total porosity (%) = (1 − bulk density ÷ particle density) × 100, assessing soil looseness, aeration, and water retention.
Input Data
Results
At a glance:Enter soil bulk density and particle density to compute total porosity (%) = (1 − bulk density ÷ particle density) × 100, assessing soil looseness, aeration, and water retention.
Formula
Porosity (%) = (1 − BD ÷ PD) × 100.
$$\phi = \left(1 - \frac{\rho_b}{\rho_p}\right) \times 100\%$$$$\rho_b = \text{bulk density},\ \rho_p = \text{particle density}$$How to Use
- Enter the bulk density and particle density (g/cm³).
- The calculator returns the total porosity.
Mineral soil bulk density vs estimated porosity (particle density 2.65 g/cm³)
| Bulk density (g/cm³) | Estimated porosity (%) | Soil condition |
|---|---|---|
| 1.0 | 62.3 | Loose, rich in aggregates or organic matter |
| 1.33 | 49.8 | Typical loam, about half pore space |
| 1.5 | 43.4 | Slightly tight, some crops limited |
| 1.6 | 39.6 | Near compaction threshold |
| 1.8 | 32.1 | Clearly compacted, roots hindered |
The threshold varies with texture: sandy soil tolerates higher bulk density, clay lower; this table is a general guide for mineral soils.
FAQ
What if I don't know the particle density?
Mineral soils are mainly silicate minerals (quartz, feldspar) with an average particle density around 2.65 g/cm³; using this value when unmeasured is a common and reasonable approximation. But organic-rich soils have lower particle density (~1.3–1.5), so using 2.65 directly overestimates porosity; measure it or correct for organic-matter content.
What is the difference between bulk and particle density?
Bulk density is dry-soil mass per total volume (solids + pores), so it is strongly affected by compaction and structure; particle density is the density of the solid mineral phase alone, excluding pores, and is a material constant. Porosity uses exactly this difference: solid fraction = bulk density ÷ particle density, the rest is pore space. So only bulk density changes with compaction; particle density is essentially fixed.
What porosity is good?
Mineral soil total porosity is commonly 40–60%, with about half being ideal to balance aeration and water retention. Below ~40% (high bulk density) usually means compaction and insufficient aeration/infiltration; but higher is not always better — too high (very loose or high organic matter) may lack water retention or support. More important is the pore-size distribution (the ratio of large aeration pores to capillary water-holding pores), read further from the water-retention curve.
How do I measure bulk density correctly?
Standard practice uses a known-volume metal core (ring cutter) to take undisturbed soil (structure intact), bring it back with the ring, oven-dry at 105°C to constant weight, then divide dry soil mass by the ring's inner volume. Always use undisturbed soil; disturbed, sieved, or backfilled soil destroys the pore structure and distorts both bulk density and estimated porosity.
Does this porosity include water-filled pores?
Yes, this formula gives total porosity — the share of all pores (whether filled with air or water at the moment) in total volume, independent of moisture state. To know how much pore space is currently air-filled (aeration porosity) or water-filled, combine with volumetric water content: aeration porosity = total porosity − volumetric water content. When saturated, water nearly fills all pores and volumetric water content approaches total porosity.
Related Tools
References
Content review: Calculatorism Science Team. Results are for reference only; please refer to the relevant authorities for the official figures.