Bulk Density Calculator

Bulk (moist) density is the total mass of the moist sample divided by the total volume it occupies: rho_bulk = M / V.

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Enter Values

Total (moist) mass of sample

Total volume of sample

Water content w (%) — optional, for dry density

Enter your values and press Calculate to see results.

Before you rely on this: First-pass guide only. Verify safety-critical or regulated work against the relevant standards, your project requirements and a qualified professional.

How to use this calculator

Enter the total moist mass of the sample (as sampled, before drying) in grams.
Enter the total volume of the sample in cubic centimetres — for a core cutter or mould this is the known internal volume.
Optionally enter the gravimetric water content w (%) to also get the dry density; leave it blank for bulk (moist) density only.

How it works

Bulk (moist) density is the total mass of the moist sample divided by the total volume it occupies: rho_bulk = M / V. Because the moist mass includes pore water, this is the density in the ground as sampled. The result is shown in kg/m3 and in g/cm3, which is numerically equal to tonnes per cubic metre (t/m3).

When you supply the gravimetric water content w (mass of water / mass of dry solids x 100), the dry density is back-calculated as rho_dry = rho_bulk / (1 + w/100). This removes the pore-water mass so you can compare against a target dry density (e.g. from a Proctor test) for compaction control. Both densities assume the measured volume is the true total volume of the sample.

Worked example

Core-cutter sample: bulk and dry density. A 1000 cm3 core-cutter sample of moist soil weighs 1850 g, with a measured water content of 12.5%. Bulk density = 1850 g / 1000 cm3 = 1.85 g/cm3 = 1,850 kg/m3. Dry density = 1.85 / (1 + 12.5/100) = 1.85 / 1.125 = 1.6444 g/cm3 = 1,644.4 kg/m3.

Common mistakes

Entering the dry mass instead of the total moist mass — bulk density needs the as-sampled (wet) mass; use dry mass only if you specifically want dry density directly.
Mixing units. Mass must be in grams and volume in cm3 so that the g/cm3 result is correct; a 1000 cm3 mould is 1 litre, not 1 cm3.
Treating water content as (water / total mass). The standard gravimetric water content w is water divided by DRY solids, which is what the dry-density formula rho_bulk / (1 + w/100) assumes.

Frequently asked questions

What is the difference between bulk density and dry density?

Bulk (moist) density includes the mass of pore water, so it is the mass of the moist sample over its total volume. Dry density counts only the solid particles: dry density = bulk density / (1 + w/100), where w is the water content. For the same soil, dry density is always lower than bulk density.

Why is g/cm3 the same as t/m3?

There are 1,000,000 cm3 in a cubic metre and 1,000,000 g in a tonne, so 1 g/cm3 equals 1 t/m3 (and 1000 kg/m3). That is why this tool shows both units — the numeric value in g/cm3 is identical to the value in t/m3.

Is this the same as the specific gravity or particle density of the soil?

No. Bulk and dry density are mass over the TOTAL volume (including voids). Particle density (or specific gravity Gs) is the mass of solids over the volume of solids only, and is typically around 2.65-2.70 for common minerals. Bulk and dry density are always lower because they include the pore space.

Tip: Enter any known values to calculate the remaining results.

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