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Calculate soil bulk density using the standard core method, and derive total porosity and solid fraction from particle density.
Enter core volume, wet and dry soil weights, and particle density (default 2.65 g/cm³). The calculator returns bulk density, water content, total porosity and solid fraction.
Your field was yielding 8 t/ha corn last year and 5 t/ha this year. The subsoil layer felt hard under the spade. A 100 cm³ core weighed 145 g wet and 125 g dry — that is 1.25 g/cm³, not bad. But the traffic layer came in at 1.7 g/cm³, and roots could not penetrate it.
✓ Expert Reviewed: This calculator and its content have been reviewed by agricultural experts. Formulas are based on standard extension service recommendations. For site-specific advice, consult your local agronomist.
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.
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).
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%.
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: 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.
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.
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.
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.
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.
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.