How do I calculate the density of a rock?

Divide its mass by its volume. Weigh the rock, then measure the water it displaces in a graduated cylinder (1 mL = 1 cm³). A 180 g rock that raises the water by 60 mL has a density of 180 ÷ 60 = 3.00 g/cm³, or 3,000 kg/m³, which falls in the basalt and gabbro ranges.

How do I find specific gravity by weighing a rock in water?

Weigh the dry rock in air, then hang it from the scale on a thin thread fully under water without touching the container and read the apparent weight. Specific gravity = weight in air ÷ (weight in air − weight in water). A rock that weighs 265 g in air and 165 g in water has SG = 265 ÷ 100 = 2.65, typical of quartz. Multiply by the water density (0.998 g/cm³ at 20 °C) to get 2.645 g/cm³.

What is the density of granite?

Granite typically has a density of 2.63–2.75 g/cm³ (about 164–172 lb/ft³), with a commonly cited average of 2.70 g/cm³. A solid cubic yard of granite therefore weighs about 2.3 short tons.

How much does a boulder weigh?

Multiply its volume by the rock density. Boulders are closer to an ellipsoid than a box, so use volume = π ÷ 6 × length × width × height. A granite boulder 3 ft × 2 ft × 2 ft is about 6.28 ft³; at 168 lb/ft³ it weighs roughly 1,055 lb. Treating it as a box would overstate the weight by about 90%.

What is bulk density versus grain density?

Bulk density is the total mass divided by the total volume, including pores. Grain density counts only the solid minerals (2.65 g/cm³ for quartz, 2.71 for calcite). Porosity = 1 − bulk density ÷ grain density, so a sandstone with a bulk density of 2.20 g/cm³ and quartz grains has a porosity of about 17%.

Is specific gravity the same as density?

Specific gravity is a dimensionless ratio to the density of water. It is numerically almost equal to density in g/cm³ because water is about 1.000 g/cm³ at 4 °C and 0.998 g/cm³ at 20 °C, but it has no unit.

How do I convert rock density to lb/ft³ or kN/m³?

Multiply g/cm³ by 62.428 to get lb/ft³, by 1,000 to get kg/m³, and by 9.807 to get unit weight in kN/m³. Basalt at 3.00 g/cm³ is 187.3 lb/ft³, 3,000 kg/m³ or 29.4 kN/m³.

Why does my result differ from the reference chart?

Natural rocks vary in composition, porosity, moisture and weathering. Air trapped on the surface during weighing in water also lowers the result, so brush off bubbles first. Treat the chart as typical ranges, not a definitive identification.

Does crushed rock or gravel weigh the same as solid rock?

No. Loose crushed stone has 30–45% voids between pieces, so a cubic yard of gravel weighs about 1.3–1.5 short tons, while a solid cubic yard of granite weighs about 2.3 tons. Use a gravel calculator for loose material.

Rock Density Calculator

Enter a rock sample's mass and volume, or its weight in air and in water, to get bulk density, specific gravity and porosity, then compare with a chart of 36 rocks and minerals or estimate a boulder's weight.

Most common rocks have a density between about 2.0 and 3.0 g/cm³ (2,000 to 3,000 kg/m³, or 125 to 187 lb/ft³).

Sample Measurements

Mass

Volume

1 mL = 1 cm³ — use water displacement for irregular shapes.

Grain density for porosity (optional, g/cm³)

Boulder & Block Weight

Weight = volume × density. Uses the midpoint of the chosen rock's range; edit the density to use your own.

Rock

Density (g/cm³)

Shape

Unit

Length

Width

Height

Volume—

Weight—

Metric—

Density of Common Rocks & Minerals

Range in g/cm³; kg/m³, lb/ft³ and short tons per solid cubic yard at the midpoint. Rows matching your result are highlighted.

Rock / Mineral	Type	g/cm³	kg/m³	lb/ft³	tons/yd³
Granite	Igneous	2.63 – 2.75	2,690	168	2.27
Basalt	Igneous	2.70 – 3.30	3,000	187	2.53
Gabbro	Igneous	2.85 – 3.12	2,985	186	2.52
Rhyolite	Igneous	2.35 – 2.70	2,525	158	2.13
Obsidian	Igneous	2.35 – 2.60	2,475	155	2.09
Pumice	Igneous	0.35 – 0.90	625	39	0.53
Andesite	Igneous	2.40 – 2.80	2,600	162	2.19
Diorite	Igneous	2.80 – 3.00	2,900	181	2.44
Sandstone	Sedimentary	1.85 – 2.68	2,265	141	1.91
Limestone	Sedimentary	2.10 – 2.72	2,410	150	2.03
Shale	Sedimentary	2.00 – 2.70	2,350	147	1.98
Dolomite	Sedimentary	2.60 – 2.90	2,750	172	2.32
Coal	Sedimentary	1.10 – 1.60	1,350	84	1.14
Rock Salt (Halite)	Sedimentary	2.10 – 2.20	2,150	134	1.81
Chalk	Sedimentary	1.55 – 2.10	1,825	114	1.54
Conglomerate	Sedimentary	2.00 – 2.60	2,300	144	1.94
Marble	Metamorphic	2.65 – 2.87	2,760	172	2.33
Quartzite	Metamorphic	2.60 – 2.70	2,650	165	2.23
Schist	Metamorphic	2.60 – 2.90	2,750	172	2.32
Gneiss	Metamorphic	2.59 – 2.84	2,715	169	2.29
Slate	Metamorphic	2.70 – 2.90	2,800	175	2.36
Phyllite	Metamorphic	2.68 – 2.80	2,740	171	2.31
Quartz	Mineral	2.63 – 2.67	2,650	165	2.23
Feldspar	Mineral	2.54 – 2.76	2,650	165	2.23
Calcite	Mineral	2.70 – 2.72	2,710	169	2.28
Olivine	Mineral	3.27 – 4.30	3,785	236	3.19
Pyrite	Mineral	4.90 – 5.20	5,050	315	4.26
Magnetite	Mineral	5.17 – 5.18	5,175	323	4.36
Hematite	Mineral	4.90 – 5.30	5,100	318	4.30
Galena	Mineral	7.40 – 7.60	7,500	468	6.32
Gold	Mineral	15.60 – 19.30	17,450	1,089	14.71
Muscovite	Mineral	2.76 – 3.00	2,880	180	2.43
Biotite	Mineral	2.76 – 3.10	2,930	183	2.47
Gypsum	Mineral	2.30 – 2.37	2,335	146	1.97
Talc	Mineral	2.58 – 2.83	2,705	169	2.28
Fluorite	Mineral	3.17 – 3.18	3,175	198	2.68

Solid rock only. Loose crushed stone and gravel contain 30–45% voids, so a cubic yard weighs about 1.3–1.5 short tons, not the 2.2–2.5 tons of solid rock.

Method, worked examples & references

Mass and volume. Bulk density ρ = m ÷ V, where V is the total volume including pores (by water displacement or by measuring a regular shape). Example: 180 g that displaces 60 mL gives 3.00 g/cm³ (basalt or gabbro range).

Weigh in water (Archimedes). The water pushes up with a force equal to the weight of water displaced, so V = (W_air − W_water) ÷ ρ_water and SG = W_air ÷ (W_air − W_water). Example: 265 g in air and 165 g in water gives SG 2.65 and ρ = 2.65 × 0.99821 = 2.645 g/cm³ at 20 °C. Porous rocks soak up water during weighing; for an accurate bulk density, seal or saturate the sample first.

Porosity. φ = 1 − ρ_bulk ÷ ρ_grain. A sandstone at 2.20 g/cm³ made of quartz (2.65) has φ = 1 − 2.20 ÷ 2.65 = 17%.

Units. 1 g/cm³ = 1,000 kg/m³ = 62.42796 lb/ft³ = 0.8428 short tons per cubic yard; unit weight in kN/m³ = g/cm³ × 9.807. Water density by temperature follows standard tables (0.99997 g/cm³ at 4 °C, 0.99821 at 20 °C).

Conversions follow the NIST Guide to the SI. Reference ranges are indicative and follow the USGS bulk-density table, the USGS physical-property dataset and standard geophysics texts; measured density varies with porosity, moisture, weathering and composition.

Privacy: measurements and calculations remain in this browser tab.

Quick answer

Most common rocks have a density between about 2.0 and 3.0 g/cm³ (2,000 to 3,000 kg/m³, or 125 to 187 lb/ft³). Granite is 2.63–2.75 g/cm³, basalt 2.70–3.30, and porous rocks such as sandstone can be as light as 1.85.

Examples

Rock	g/cm³	lb/ft³ (typical)
Granite	2.63 – 2.75	168
Basalt	2.70 – 3.30	187
Marble	2.65 – 2.87	172
Limestone	2.10 – 2.72	150
Sandstone	1.85 – 2.68	141
Pumice	0.35 – 0.90	39

Enter your sample's mass and volume, or weigh it in water, to get its density and see which rock ranges it matches.

Summary

The Rock Density Calculator computes bulk density from a sample’s mass and total volume, or from its weight in air and its apparent weight in water (Archimedes’ method). It reports g/cm³, kg/m³, specific gravity, unit weight in lb/ft³ and, if you give a grain density, porosity. A server-rendered chart lists 36 rocks and minerals, and a weight estimator turns a block or boulder size into pounds, kilograms and tons.

How it works

Pick a method: mass and volume, or weigh in water.
Mass and volume: enter the mass (g, kg, oz, lb) and total volume (cm³, mL, L, m³, in³, ft³). Density = mass ÷ volume.
Weigh in water: enter the dry weight in air and the apparent weight while fully submerged and hanging from the scale. Specific gravity = W(air) ÷ (W(air) − W(water)); density = specific gravity × water density at the chosen temperature.
Optionally enter a grain density (2.65 for quartz sandstone, 2.71 for limestone) to estimate porosity = 1 − bulk ÷ grain density.
The comparison panel lists every reference range that contains your result, and matching rows are highlighted in the chart.
To weigh a boulder or block, choose a rock (or type a density), a shape and three dimensions.

Use cases

Geology fieldwork: check whether a hand sample matches expected density ranges.
Classroom labs: measure density by displacement or by weighing in water.
Rockhounding: separate heavy ore minerals (pyrite, galena, hematite) from ordinary rock by specific gravity.
Landscaping and moving: estimate the weight of a boulder before renting equipment.
Civil engineering: estimate unit weight of rock in lb/ft³ or kN/m³ for preliminary design.
Petrophysics: estimate porosity from bulk and grain density.

Frequently Asked Questions

Last updated: 2026-10-09 · Reviewed by Nham Vu