Rock Density Calculator

Volume method

Pick how you will obtain the sample volume.

Mass

Use dry mass when reporting standard density.

Rounding

Applies to display values and exports.

Volume

1 mL equals 1 cm3 for water-based measurements.

Shape

Choose the closest geometry to your sample.

Length unit

Used for all dimension-based volume formulas.

Length (L)

Width (W)

Height (H)

Diameter (D)

Length (L)

Diameter (D)

Initial water level

Final water level

Level unit

Volume = Final − Initial.

Core input mode

Useful for drilled cores and lab plugs.

Core diameter (D)

Core length (L)

Cross‑section area (A)

Area unit

Core length (L)

Estimate grain density from porosity

Propagate measurement uncertainty

Optional tools for lab-style reporting.

Porosity (%)

Grain density ≈ bulk density ÷ (1 − φ).

Mass uncertainty (±)

Uses the same unit as the mass input.

Volume uncertainty (±)

Choose the uncertainty unit below.

Uncertainty unit

Used for density uncertainty propagation.

Example data table

These sample values illustrate typical densities. Real samples vary with porosity, mineralogy, and moisture.

Sample	Mass (g)	Volume (cm3)	Density (g/cm3)	Specific gravity	Notes
Granite	265.0	100.0	2.65	2.65	Common felsic igneous rock.
Basalt	295.0	100.0	2.95	2.95	Mafic rock, often higher density.
Limestone	240.0	100.0	2.40	2.40	Carbonate rock; porosity can be significant.
Sandstone	220.0	100.0	2.20	2.20	Bulk density drops with higher pore space.
Shale	250.0	100.0	2.50	2.50	Fine-grained sedimentary rock.
Pumice	65.0	100.0	0.65	0.65	Highly vesicular; may float on water.

Formula used

Density: ρ = m / V where m is mass and V is volume.
Rectangular block: V = L × W × H
Cylinder: V = π × (D/2)² × L
Sphere: V = (4/3) × π × (D/2)³
Displacement: V = V₂ − V₁ using the water level change.
Specific gravity: SG ≈ ρ / ρwater. This tool uses ρwater = 1 g/cm3 for a clean reference.
Grain density estimate: ρgrain ≈ ρbulk / (1 − φ), where φ is porosity as a fraction.
Uncertainty (propagation): (Δρ/ρ) = √[(Δm/m)² + (ΔV/V)²]

How to use this calculator

Measure the sample mass on a balance and select its unit.
Choose a volume method that matches your sample shape.
Enter the required volume fields and units for that method.
Enable porosity or uncertainty tools if you need them.
Press Calculate to see results above the form.
Use the download buttons to export your latest result.

Bulk density links mass, minerals, and pore space

Bulk density is the mass of a rock divided by its total volume, including pores. It reflects mineral composition, crystal packing, and void fraction. Quartz is about 2.65 g/cm3, calcite about 2.71 g/cm3, and olivine commonly exceeds 3.2 g/cm3, so mineral mixing shifts measured values. Moisture can raise mass without changing solid volume, so dry, constant‑temperature measurements improve comparability across laboratories.

Choose a volume method that matches sample geometry

For regular shapes, geometric volume is fast: blocks use L×W×H and cylinders use π(D/2)²L. For irregular fragments, water displacement is practical when you remove trapped air. Record initial and final meniscus readings and keep the same unit, because 1 mL equals 1 cm3. Core plugs are best treated as cylinders; measuring diameter twice and averaging reduces ovality bias.

Report units and conversions in a consistent format

This calculator standardizes to g and cm3, then displays g/cm3, kg/m3, and lb/ft3. Remember that 1 g/cm3 equals 1000 kg/m3, so a 2.70 g/cm3 limestone corresponds to 2700 kg/m3. When comparing field and lab data, confirm whether masses were recorded in kilograms and volumes in liters, because a misplaced factor of 1000 is common.

Add uncertainty to support quality control decisions

Density uncertainty can be estimated from measurement uncertainties using √[(Δm/m)²+(ΔV/V)²]. For example, m=250.0±0.1 g and V=100.0±0.5 cm3 yields a relative uncertainty of about 0.51%, so a 2.50 g/cm3 result carries roughly ±0.013 g/cm3. Repeating measurements and comparing spreads across specimens helps detect bubbles, chipped edges, or scale drift.

Interpret results using realistic rock density ranges

Many sedimentary rocks cluster near 2.0–2.6 g/cm3, felsic igneous rocks often sit around 2.6–2.8 g/cm3, and mafic rocks commonly reach 2.8–3.1 g/cm3. Pumice can be below 1.0 g/cm3 due to vesicles. If you enter porosity, grain density rises as ρbulk/(1−φ), supporting comparisons between porous and compact samples.

FAQs

1) What is the difference between bulk density and grain density?

Bulk density uses total volume, including pores. Grain density represents the solid minerals only. If porosity is known, grain density can be estimated as bulk density divided by (1 − porosity fraction).

2) Why does the calculator show specific gravity?

Specific gravity is density relative to water. Using 1 g/cm3 as the reference, the numeric value matches density in g/cm3, making comparisons easy when classifying samples or checking plausibility.

3) Which method is best for irregular rocks?

Water displacement is usually best for irregular shapes. Submerge slowly, remove bubbles, and read the meniscus consistently. The volume equals the final reading minus the initial reading.

4) Can I use wet mass from a freshly collected sample?

You can, but it may overestimate density because water adds mass. For comparable reporting, dry the sample to constant mass, cool it in a desiccator, then weigh and measure volume.

5) How do I avoid unit mistakes?

Keep a single unit system from start to finish and confirm conversions. Remember 1 mL equals 1 cm3 and 1 g/cm3 equals 1000 kg/m3. Recheck any value that changes by a factor of 10 or 1000.

6) What does an unusually high density suggest?

Very high results can indicate iron‑rich minerals, sulfides, or ultramafic material. They can also come from incorrect volume entry or trapped air during displacement. Verify measurements, repeat the volume step, and confirm the selected units.

Tip: For irregular rocks, water displacement often gives the best practical volume estimate.