API = 141.5/SG(60°F) − 131.5. Used for crude oil grading. Water = 10° API. Light crude: >31° API. Heavy: <22° API.

Ice density is 917 kg/m³ — less than liquid water (999.84 kg/m³ at 0°C). Water expands ~9% when freezing due to hexagonal hydrogen-bond crystal structure.

⚖️ Density Conversion Calculator

Convert between kg/m³, g/cm³, g/mL, lb/ft³, lb/gal, oz/in³, t/m³, mg/L and 50+ density units — with fundamental density formula ρ=m/V, specific gravity, Archimedes' principle, buoyancy, API gravity & material density table rendered in MathJax

50+ Units SI · CGS · Imperial · Grain · Water-Reference kg/m³ ↔ g/cm³ · lb/ft³ · g/mL Free & Instant

🔄 Density Unit Converter

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1 kg/m³ = 0.001 g/cm³

Formula: value × 0.001

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💡 Definition: Density \(\rho = m/V\) — mass per unit volume. SI unit: kg/m³. Note: \(1\,\text{g/cm}^3 = 1\,\text{g/mL} = 1000\,\text{kg/m}^3\) (exact). Water at 4°C: \(\rho_w = 1000\,\text{kg/m}^3\) (maximum density — basis of specific gravity).

📖 How to Use This Density Conversion Calculator

1

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Click SI/Metric (kg/m³, g/cm³, g/L, t/m³, mg/L), Imperial/US (lb/ft³, lb/in³, lb/gal, oz/in³), Grain-Based (gr/gal, gr/ft³), or Water Reference (relative to water at 4°C, 20°C, ice) to narrow the dropdowns.
2

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Type the numeric density value. Accepts any range — from µg/L (trace contaminant analysis) to kg/cm³ (ultra-dense materials like osmium or neutron star crusts).
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Click presets — kg/m³↔g/cm³, kg/m³↔lb/ft³, g/cm³→lb/ft³, kg/m³→lb/gal, lb/in³→kg/m³ — for the most common density conversions in engineering and laboratory use.
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📐 Density Unit Conversion Reference Table

From	To	Multiply By	Mathematical Expression
1 g/cm³	kg/m³	1,000	\( 1\,\text{g/cm}^3 = 10^3\,\text{kg/m}^3 \)
1 kg/m³	g/cm³	0.001	\( 1\,\text{kg/m}^3 = 10^{-3}\,\text{g/cm}^3 \)
1 lb/ft³	kg/m³	16.01846	\( 1\,\text{lb/ft}^3 = 16.01846\,\text{kg/m}^3 \)
1 kg/m³	lb/ft³	0.062428	\( 1\,\text{kg/m}^3 = 0.062428\,\text{lb/ft}^3 \)
1 lb/in³	kg/m³	27,679.9	\( 1\,\text{lb/in}^3 = 27{,}679.9\,\text{kg/m}^3 \)
1 lb/gal (US)	kg/m³	119.826	\( 1\,\text{lb/gal (US)} = 119.826\,\text{kg/m}^3 \)
1 t/m³	kg/m³	1,000	\( 1\,\text{t/m}^3 = 10^3\,\text{kg/m}^3 \)
1 g/L	kg/m³	1	\( 1\,\text{g/L} = 1\,\text{kg/m}^3 \) (exact)
1 mg/L	kg/m³	0.001	\( 1\,\text{mg/L} = 10^{-3}\,\text{kg/m}^3 \)
1 oz/in³	kg/m³	1,729.99	\( 1\,\text{oz/in}^3 = 1{,}730.0\,\text{kg/m}^3 \)

⚖️ Understanding Density — A Complete Science & Engineering Guide

Density is one of the most practically important physical properties in science and engineering. It tells you exactly how much mass is packed into a given volume — and this single number determines whether objects float or sink, how structures bear load, whether alloys meet specification, how pharmaceutical tablets dissolve, how petroleum products are graded, and even how oceanographic water masses circulate around the globe driving the entire climate system.

Converting between density units accurately is essential across many disciplines: a materials engineer comparing aluminium alloys in kg/m³ and lb/in³, a chemist measuring solution concentrations in g/mL, a petroleum engineer using API gravity, a water treatment specialist working in mg/L and grains per gallon, and a food scientist measuring ingredient densities in lb/ft³ all need reliable, precise unit conversion. This calculator covers all of them.

Density — Fundamental Definition

\[ \rho = \frac{m}{V} \qquad m = \rho V \qquad V = \frac{m}{\rho} \]

\(\rho\) = density (kg/m³) · \(m\) = mass (kg) · \(V\) = volume (m³) · SI unit: kg/m³ · CGS unit: g/cm³ (= g/mL) · Imperial: lb/ft³ · Note: \(1\,\text{g/cm}^3 = 1000\,\text{kg/m}^3\) exactly

📦 Density Unit Systems — SI, CGS, & Imperial Explained

Density is expressed in fundamentally different units depending on the field and region. Understanding what each unit means — and exactly how they relate — prevents costly errors in engineering specifications, chemical formulations, and material procurement.

SI, CGS & Imperial — Exact Relationships

\( 1\,\text{g/cm}^3 = 1\,\text{g/mL} = 1\,\text{kg/L} = 1\,\text{t/m}^3 = 1000\,\text{kg/m}^3 \quad \text{(all exact)} \)

\( 1\,\text{lb/ft}^3 = 16.01846337...\,\text{kg/m}^3 \quad \text{(from 1 lb = 0.45359237 kg, 1 ft = 0.3048 m)} \)

\( 1\,\text{lb/in}^3 = \frac{0.45359237}{(0.0254)^3} = 27{,}679.904...\,\text{kg/m}^3 \)

\( 1\,\text{lb/gal (US)} = \frac{0.45359237}{3.785411784 \times 10^{-3}} = 119.826\,\text{kg/m}^3 \)

\( 1\,\text{g/L} = 1\,\text{kg/m}^3 = 1\,\text{mg/mL} \quad \text{(exact: 1 L = 10}^{-3}\text{ m}^3\text{)} \)

All Imperial conversion factors derived from the 1959 International Yard and Pound Agreement (1 lb = 453.59237 g, 1 in = 25.4 mm — exact). US gallon = 231 in³ = 3.785411784 L (exact). UK gallon = 4.54609 L (exact, defined 1985).

📌 Worked Example — Steel Density Conversion (g/cm³ → kg/m³ → lb/ft³ → lb/in³)

Problem: AISI 1020 carbon steel has density 7.87 g/cm³. Convert to kg/m³, lb/ft³, and lb/in³.

kg/m³: \( 7.87\,\text{g/cm}^3 \times 1000 = \mathbf{7{,}870\,\text{kg/m}^3} \)

lb/ft³: \( 7{,}870 \div 16.01846 = \mathbf{491.3\,\text{lb/ft}^3} \)

lb/in³: \( 7{,}870 \div 27{,}679.9 = \mathbf{0.2843\,\text{lb/in}^3} \)

Practical use: A steel I-beam with volume 0.05 m³: \( m = \rho V = 7{,}870 \times 0.05 = \mathbf{393.5\,\text{kg}}\). An engineer using lb/ft³ calculates: \(491.3 \times 1.766\,\text{ft}^3 = 867.5\,\text{lb} = 393.5\,\text{kg}\). Same answer — unit conversion done right.

💧 Specific Gravity — Dimensionless Density Ratio

Specific gravity (SG), also called relative density, is the ratio of a substance's density to the density of a reference substance — usually water at 4°C (1,000 kg/m³ = 1 g/cm³) for liquids and solids. Because it is a pure ratio, SG is dimensionless — it has no units. This makes it especially convenient for quick material identification, quality control, and international communication where unit systems differ.

Specific Gravity — Definition & Conversions

\( SG = \frac{\rho_{\text{substance}}}{\rho_{\text{water at 4°C}}} = \frac{\rho}{1000\,\text{kg/m}^3} \)

\( \rho\,[\text{kg/m}^3] = SG \times 1000 \qquad \rho\,[\text{g/cm}^3] = SG \times 1\,\text{g/cm}^3 \)

\( \text{API gravity} = \frac{141.5}{SG_{60°F}} - 131.5 \qquad \Leftrightarrow \qquad SG = \frac{141.5}{\text{API} + 131.5} \)

\( \text{Baumé (heavy): } {}^{\circ}\text{Bé} = 145 - \frac{145}{SG} \qquad \text{Baumé (light): } {}^{\circ}\text{Bé} = \frac{140}{SG} - 130 \)

SG < 1: substance floats on water (e.g., wood, ice at 0.917, petrol at ~0.73) · SG = 1: same density as water · SG > 1: sinks (e.g., steel at 7.87, gold at 19.3) · API gravity reference: 60°F (15.6°C) · Water API = 10° exactly

🛢️ API Gravity in Oil Industry: API gravity is the standard petroleum density scale. Light crude oil: API > 31° (SG < 0.871) — highest value, easiest to refine. Medium crude: API 22–31° (SG 0.871–0.920). Heavy crude: API 10–22° (SG 0.920–1.000). Extra-heavy: API < 10° (SG > 1.000 — sinks in water). West Texas Intermediate (WTI) benchmark: ~40° API (SG ≈ 0.825). Venezuela's Orinoco Belt: ~8° API (SG ≈ 1.015).

🌊 Archimedes' Principle — Buoyancy & Density Measurement

Archimedes' Principle (c. 250 BCE) is the fundamental theorem connecting density and buoyancy: any object immersed in a fluid experiences an upward buoyant force equal to the weight of the fluid it displaces. This principle not only explains floating and sinking but is also the basis of some of the most accurate density measurement techniques used today — including hydrostatic weighing and pycnometry.

Archimedes' Principle & Buoyancy

\( F_b = \rho_{\text{fluid}} \cdot V_{\text{displaced}} \cdot g \qquad \text{(buoyant force)} \)

\( \text{Object floats if: } \rho_{\text{object}} < \rho_{\text{fluid}} \qquad \text{Object sinks if: } \rho_{\text{object}} > \rho_{\text{fluid}} \)

\( \text{Fraction submerged} = \frac{\rho_{\text{object}}}{\rho_{\text{fluid}}} \qquad \text{(floating equilibrium)} \)

\( \rho_{\text{solid}} = \frac{m_{\text{air}}}{m_{\text{air}} - m_{\text{fluid}}} \cdot \rho_{\text{fluid}} \qquad \text{(hydrostatic weighing — density measurement)} \)

\(F_b\) = buoyant force (N) · \(\rho_{\text{fluid}}\) = fluid density (kg/m³) · \(V_{\text{displaced}}\) = volume of fluid displaced (m³) · \(g\) = 9.80665 m/s² · Hydrostatic weighing achieves density accuracy to 0.01% for solids — used in metallurgy, gemology, and pharmaceutics

📌 Worked Example — Ice Floating on Water (Fraction Submerged)

Problem: An iceberg has density 917 kg/m³. What fraction is submerged in seawater (ρ = 1,025 kg/m³)?

\[ \text{Fraction submerged} = \frac{\rho_{\text{ice}}}{\rho_{\text{seawater}}} = \frac{917}{1{,}025} = \mathbf{0.8946} \approx 89.5\% \]

Interpretation: Only ~10.5% of an iceberg protrudes above the ocean surface. The famous "iceberg tip" phenomenon is a direct consequence of density ratios. In fresh water (1,000 kg/m³): fraction = 917/1,000 = 91.7% submerged, so 8.3% above — slightly more visible than in saltwater.

💧 Water Density — Temperature Dependence & the 4°C Maximum

Water Density at Key Temperatures

\( \rho_{\text{water}}(4°\text{C}) = 999.9720\,\text{kg/m}^3 \approx 1000\,\text{kg/m}^3 \quad \text{(maximum density)} \)

\( \rho_{\text{water}}(20°\text{C}) = 998.204\,\text{kg/m}^3 \qquad \rho_{\text{water}}(100°\text{C}) = 958.4\,\text{kg/m}^3 \)

\( \rho_{\text{ice}}(0°\text{C}) = 916.8\,\text{kg/m}^3 \qquad \text{(water expands }\approx 9\%\text{ on freezing)} \)

\( \rho_{\text{seawater}} \approx 1020\text{–}1029\,\text{kg/m}^3 \qquad \text{(salinity 33–37 g/kg)} \)

Water reaches maximum density at 4°C due to the balance between thermal contraction (cooling) and crystal-lattice hydrogen-bonding expansion (near freezing). Below 4°C, hydrogen bonds dominate — water expands as it approaches 0°C. This anomalous expansion causes ice to float, which is critical for aquatic life in cold climates.

🌊 Thermohaline circulation: Ocean density differences driven by temperature (thermo-) and salinity (haline) differences power the global "conveyor belt" ocean circulation. Cold, salty water at the poles (density ~1,028 kg/m³) sinks, while warm tropical surface water (density ~1,022 kg/m³) is less dense and flows poleward. This density-driven circulation controls heat distribution across the globe — a 0.001 g/cm³ (1 kg/m³) density difference can drive massive oceanic flows.

🪨 Material Density Reference Table

Material	kg/m³	g/cm³	lb/ft³	Notes
🌡️ Air (20°C, 1 atm)	1.204	0.001204	0.0752	Composition-dependent
🌊 Fresh water (4°C)	999.97	1.000	62.43	Maximum density
🌊 Seawater (15°C)	1,025	1.025	64.0	Salinity ~35 g/kg
🧊 Ice (0°C)	917	0.917	57.25	Floats due to low density
🛢️ Petroleum (crude)	800–900	0.80–0.90	50–56	API 25–45°
🪵 Oak wood	600–900	0.6–0.9	37–56	Varies with moisture content
🏗️ Concrete	2,300–2,400	2.30–2.40	144–150	Reinforced: ~2,400
🧱 Aluminium (pure)	2,702	2.702	168.7	Most-used structural metal
🔩 Iron	7,874	7.874	491.5	Body-centred cubic
🔩 Steel (carbon)	7,750–8,050	7.75–8.05	484–503	Alloy composition varies
🪙 Copper	8,960	8.96	559.5	High conductivity metal
🏗️ Lead	11,340	11.34	708.0	Radiation shielding
🏅 Gold	19,282	19.28	1,204	Denser than most metals
⚫ Osmium (densest element)	22,590	22.59	1,410	Densest naturally occurring element

🔬 Density Measurement Methods & Applications

⚗️

Pycnometry — Laboratory Standard

Measures density using a precisely calibrated volume vessel (pycnometer). Accuracy: 0.001–0.0001 g/cm³. Used for liquids (ASTM D1217), solids (ASTM D792), and powders. Formula: \(\rho = m_s \rho_f / (m_s + m_f - m_{sf})\)

🌡️

Hydrometer — Field & Process Use

Floats in liquid at equilibrium where buoyancy = weight. Reads specific gravity or Baumé scale directly. Used in winemaking (must density), brewing (Plato scale), battery acid (sulfuric acid SG), anti-freeze (ethylene glycol), and seawater salinity.

📡

Vibrating Tube — Process Control

Measures resonant frequency of a U-tube containing the fluid; frequency changes with density. Digital density meters (Anton Paar, Mettler Toledo) achieve ±0.00001 g/cm³. Used in pharmaceutical QC, beverage production, petroleum refining.

🔬

X-ray / Gamma Densitometry

Radiation transmission through materials inversely related to density: \(I = I_0 e^{-\mu \rho x}\). Non-invasive; used for measuring concrete density, food product consistency, and pipeline particulate concentration without contact.

💨 Gas Density — Ideal Gas Law

Ideal Gas Density — Temperature & Pressure Dependence

\( PV = nRT \qquad \Rightarrow \qquad \rho_{\text{gas}} = \frac{PM}{RT} \)

\( \rho_{\text{air, STP}} = \frac{101{,}325 \times 0.02897}{8.314 \times 273.15} = \mathbf{1.293\,\text{kg/m}^3} \quad \text{(0°C, 1 atm)} \)

\( \rho_{\text{air, NTP}} = \frac{101{,}325 \times 0.02897}{8.314 \times 293.15} = \mathbf{1.204\,\text{kg/m}^3} \quad \text{(20°C, 1 atm)} \)

\( \rho_2 = \rho_1 \cdot \frac{P_2 T_1}{P_1 T_2} \qquad \text{(scaling gas density with P and T)} \)

\(P\) = pressure (Pa) · \(M\) = molar mass (kg/mol) · \(R\) = 8.31446 J/(mol·K) · \(T\) = absolute temperature (K) · STP = 0°C, 101.325 kPa (IUPAC 1982) · NTP = 20°C, 101.325 kPa · SATP = 25°C, 100 kPa (IUPAC 1980)

Written & Reviewed by Num8ers Editorial Team — Materials Science, Chemical Engineering, Petroleum Engineering & Metrology Specialists Last updated: April 2026 · Conversion factors verified against NIST SP 811 (2008), ISO 80000-4 (Mechanics), ASTM D792/D1217 (density measurement standards), 1959 International Yard and Pound Agreement, and US gallon definition (231 in³ exact). Material density data cross-referenced with ASM International Handbook of Materials Properties (2016).

❓ Frequently Asked Questions — Density Conversion

How do I convert kg/m³ to g/cm³?

Divide by 1,000. \(1\,\text{g/cm}^3 = 1000\,\text{kg/m}^3\) exactly. So: \(\rho\,[\text{g/cm}^3] = \rho\,[\text{kg/m}^3] \div 1000\). Example: Aluminium at 2,702 kg/m³ = 2.702 g/cm³. Reverse (g/cm³ to kg/m³): multiply by 1,000. This is the most common density unit conversion in engineering.

How do I convert g/cm³ to lb/ft³?

Multiply by 62.4280. \(1\,\text{g/cm}^3 = 62.4280\,\text{lb/ft}^3\). Derivation: \(1\,\text{g/cm}^3 = 1000\,\text{kg/m}^3 \div 16.01846 = 62.428\,\text{lb/ft}^3\). Example: Steel at 7.87 g/cm³ × 62.428 = 491.3 lb/ft³. Reverse (lb/ft³ to g/cm³): divide by 62.428 (or multiply by 0.016018).

How do I convert lb/ft³ to kg/m³?

Multiply by 16.01846. \(1\,\text{lb/ft}^3 = 16.01846\,\text{kg/m}^3\). Derivation from exact values: (1 lb = 0.45359237 kg) ÷ (1 ft = 0.3048 m)³ = 0.45359237/0.028316847 = 16.01846 kg/m³. Example: Water 62.43 lb/ft³ × 16.018 = 999.9 kg/m³ ≈ 1,000 kg/m³.

Is g/cm³ the same as g/mL?

Yes — exactly equal. \(1\,\text{cm}^3 = 1\,\text{mL}\) exactly (by definition of the millilitre: 1 mL = 10⁻³ L = 10⁻⁶ m³ = 1 cm³). Therefore g/cm³ = g/mL = 1000 kg/m³ = 1 kg/L. This identity is frequently used in chemistry: a liquid's density in g/mL is numerically equal to its specific gravity relative to water at 4°C.

What is the density of water at different temperatures?

Water reaches its maximum density at 4°C: 999.972 kg/m³ ≈ 1,000 kg/m³. At 20°C: 998.2 kg/m³. At 100°C: 958.4 kg/m³. Ice at 0°C: 917 kg/m³ (less dense — floats). Seawater (salinity 35 g/kg): 1,025 kg/m³ at 15°C. The temperature of maximum density decreases with salinity: seawater's maximum density point drops below its freezing point.

What is specific gravity and how does it relate to density?

Specific gravity (SG) = ρ_substance / ρ_water(4°C). Dimensionless — no units. Since ρ_water(4°C) = 1 g/cm³ = 1,000 kg/m³, numerically: SG = ρ [g/cm³] = ρ [kg/m³] / 1000. SG < 1: floats on water (petrol SG 0.72, wood SG 0.5–0.9, ice SG 0.917). SG > 1: sinks (concrete SG 2.4, steel SG 7.85, gold SG 19.3).

What is API gravity and how is it calculated?

API gravity = 141.5 / SG(60°F) − 131.5. Used for crude oil grading. Light crude: API > 31° (SG < 0.871). Heavy crude: API < 22° (SG > 0.920). Water = 10° API exactly. Example: WTI crude at SG = 0.825 → API = 141.5/0.825 − 131.5 = 171.5 − 131.5 = 40.0° API. Higher API = more valuable (easier to refine into petrol).

What is bulk density and how does it differ from true density?

True (skeletal) density = mass ÷ actual solid volume (excludes all voids). Bulk density = mass ÷ total volume including inter-particle voids and porosity. Always: bulk density < true density. Examples: Quartz true density 2,650 kg/m³, bulk density (sand) ~1,500 kg/m³ (porosity ~43%). Flour true density ~1,440 kg/m³, bulk density ~600 kg/m³. Critical for packaging, concrete mix design, and powder flow/storage.

Why does ice float on water?

Ice at 0°C has density 917 kg/m³ — less than liquid water (999.84 kg/m³ at 0°C). Water is one of very few substances that expands on freezing. The reason: water molecules form a hexagonal hydrogen-bond crystal lattice in ice that keeps molecules further apart than in liquid water. This ~9% volume expansion upon freezing makes ice less dense, so it floats. Ecological consequence: frozen lakes insulate aquatic life below the ice layer.

What is the densest naturally occurring element?

Osmium (Os) — density 22,590 kg/m³ (22.59 g/cm³), closely followed by iridium at 22,560 kg/m³. Both are platinum-group metals in the 6th period. Osmium is ~2.3× denser than iron, ~1.17× denser than gold (19,282 kg/m³). In lb/ft³: osmium = 1,410 lb/ft³. Compared to water: SG = 22.59 — nearly 23× denser. Used in fountain-pen tips, electrical contacts, and as catalyst.

What are grains per gallon (gpg) and how are they used?

1 grain/gallon (US) = 17.118 mg/L. Used in US water treatment for water hardness measurement and dissolved solids concentration. A "grain" = 1/7000 lb = 64.799 mg. Water hardness: <1 gpg = soft, 1–3.5 gpg = slightly hard, 3.5–7 gpg = moderately hard, 7–10.5 gpg = hard, >10.5 gpg = very hard. UK: grains/UK gallon = 14.254 mg/L. Used in filter sizing, water softener configuration, and pharmaceutical water specifications.

How accurate is the Num8ers Density Conversion Calculator?

Uses exact conversion factors per NIST SP 811 and the 1959 International Yard and Pound Agreement: 1 lb = 0.45359237 kg (exact); 1 ft = 0.3048 m (exact); 1 US gallon = 231 in³ = 3.785411784 L (exact); 1 UK gallon = 4.54609 L (exact). Therefore 1 lb/ft³ = 16.018463373960... kg/m³ (exact). JavaScript double precision provides ~15 significant digits — adequate for all engineering and laboratory applications.

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