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Soil Bulk Density Calculator
Calculate soil bulk density using the standard core method, and derive total porosity and solid fraction from particle density.
Results
How to Use This Calculator
Take a known-volume soil core with a metal ring, weigh it wet in the field, dry it at 105 °C for 24 hours, and weigh it again. Enter both weights and the ring volume. Click Calculate to get bulk density and porosity.
About This Tool
Bulk density is dry soil mass per unit bulk volume. It is measured by the core method, the standard approach in soil survey and extension. Porosity is derived assuming a particle density of 2.65 g/cm³ (quartz dominated mineral soils).
Applicability: Designed for temperate and subtropical soils, applicable to farming systems across North America and Europe.
How the Calculation Works
Bulk density = dry weight ÷ core volume. Bulk density (lb/ft³) = BD (g/cm³) × 62.428. Gravimetric water content = (wet − dry) ÷ dry × 100%. Total porosity = (1 − BD ÷ particle density) × 100%. Solid fraction = BD ÷ particle density × 100%.
Real-World Example
A 100 cm³ ring holds 125 g dry soil and 145 g wet soil. BD = 125 ÷ 100 = 1.25 g/cm³. Water content = (145 − 125) ÷ 125 = 16%. Porosity = (1 − 1.25 ÷ 2.65) × 100 = 52.8%.
Common Mistakes & Tips
Common mistakes: not drying at 105 °C for long enough (organic matter will burn above this temperature), over-compacting the core when inserting the ring, sampling stones or gravel, and ignoring that BD changes strongly with depth. Take multiple replicates per layer.
Reviewed by Agricalc Editorial Team — Agricultural engineers and agronomists with 10+ years of field experience. Our team verifies every calculator formula against peer-reviewed extension publications. For site-specific advice, consult your local agronomist.
References
- USDA NRCS — Soil Health Assessment
- University of Minnesota Extension — Soil Management & Health
- FAO — Soils Portal
Frequently Asked Questions
What is a good bulk density for agriculture?
Ideal topsoil BD is 1.0–1.3 g/cm³. Root growth is restricted above 1.4 g/cm³ in clays and 1.6 g/cm³ in sands. Subsoils compacted by traffic often reach 1.6–1.8 g/cm³ and require deep ripping.
Why is particle density assumed to be 2.65 g/cm³?
Most mineral soils are dominated by quartz (2.65 g/cm³) and feldspar. Organic soils have much lower particle density (0.9–1.5 g/cm³); if your soil is peat, use 1.0–1.5 instead.
How does bulk density relate to porosity?
Porosity = (1 − BD ÷ particle density) × 100%. A typical loam at BD 1.3 has about 51% porosity. As BD rises, porosity falls; below ~35% porosity, root growth is severely restricted.
How many core samples do I need?
Take at least 3–5 replicates per management zone and per soil layer. Spatial variability in a single field can be 0.2–0.3 g/cm³. Sampling by depth horizon (e.g. 0–15, 15–30, 30–45 cm) is essential to find compacted pans.
Can I measure bulk density without a core?
The sand-cone method and the rubber-balloon method are alternatives, used when rings cannot be driven (stony soils). They measure volume by displacement. The core method remains the fastest and most reproducible for fine-textured soils.
