Convert between kg/m³, g/cm³, lb/ft³, lb/gal and more — with the full conversion steps shown.
The density of a material — its mass divided by its volume — is one of the most-used numbers in science and engineering, and it is quoted in a confusing zoo of units: physicists say kg/m³, chemists say g/cm³, American engineers say lb/ft³, and the petroleum industry says lb/gal. Converting between them by hand means juggling factors like 16.0185 and 119.826, where a slipped decimal silently ruins a calculation. Our free Density Converter converts any supported density unit to any other and shows the two-step working — input to the kg/m³ base, then to the target — so you can verify every digit.
Density answers a deceptively simple question: how much stuff is packed into a given space? Water at 4°C is the universal reference at 1000 kg/m³ (exactly 1 g/cm³). Materials lighter than water float; heavier ones sink — Archimedes’ principle in one number. Engineers use density to convert between the mass they weigh and the volume they pour, design buoyancy, size pumps, and check material specifications. Getting the units right is not pedantry: the infamous Mars Climate Orbiter was lost in 1999 partly because of unit confusion, and density conversions with their awkward factors are exactly the kind of place such errors hide.
Enter any value, pick the source and target units, and the converter returns the result to four decimals plus a bonus: the ratio to water’s density, with a plain-English verdict — sink, float, or neutrally buoyant. Whether you are a student checking homework, a brewer measuring wort, or an engineer sizing a storage tank, the steps are transparent and the math is exact.
Density (ρ) is mass per unit volume: ρ = m/V. The SI unit is the kilogram per cubic meter (kg/m³), but the centimeter-gram-second world uses g/cm³ — numerically 1000× larger — and US customary engineering uses pounds per cubic foot or per gallon. Because volume itself is cubed length, density units inherit awkward cubed conversion factors: 1 g/cm³ = 1000 kg/m³, 1 lb/ft³ = 16.0185 kg/m³, and 1 lb per US gallon = 119.826 kg/m³.
Why water is the reference: liquid water’s density is very close to 1000 kg/m³ (maximum 999.972 kg/m³ at 3.98°C), so the ratio of any material’s density to water’s — called specific gravity — is nearly the same number as the density in g/cm³. A specific gravity of 2.7 (aluminum) means 2.7 g/cm³ or 2700 kg/m³. The converter’s water-ratio readout is effectively a specific-gravity calculator.
Density vs. weight density: physicists distinguish mass density (kg/m³) from weight density or specific weight (N/m³ or lbf/ft³) — the weight of a unit volume, equal to ρ·g. US engineering tables often quote “density” in lb/ft³, which is technically a mass unit only if you read “lb” as pound-mass; in practice the converter treats lb/ft³ as mass density with the standard 16.0185 factor, matching how the values are used in construction and HVAC tables.
Key terms:
Every conversion passes through the SI base kg/m³, exactly as the widget’s step line shows. The gallon here is the US liquid gallon (3.78541 L); the imperial gallon would give 99.78 kg/m³ per lb/gal — a 17% difference, which is why the converter labels its gallon explicitly.
Convert the density of water, 1 g/cm³, to pounds per cubic foot.
This is the number behind the rule of thumb that a cubic foot of water weighs about 62.4 lb — the converter reproduces the handbook value to four decimals.
Structural steel is listed at 490 lb/ft³. Express it in g/cm³.
Handbooks quote steel at 7.85 g/cm³; the converter lands within rounding — a good sanity check that the factors are right.
Maya brews beer and measures her wort with a hydrometer reading 1.052 specific gravity — that is 1.052 g/cm³, or 1052 kg/m³. Her American recipe software wants lb/gal for the grain-bill calculator. She types 1.052 g/cm³ into the converter and gets 8.764 lb/gal (1.052 × 1000 ÷ 119.826). The recipe’s expected 8.8 lb/gal confirms her mash is on target; a reading of 8.2 would have warned her the sugars didn’t convert.
The water-ratio readout does double duty here: specific gravity is the water ratio, so the converter’s “1.052× water” line is exactly what her hydrometer said. Brewers live in specific gravity, engineers live in lb/ft³, chemists live in g/cm³ — the converter is the translator between their dialects.
A second scenario: concrete. A contractor orders a slab and the mix design calls for 145 lb/ft³ normal-weight concrete. The structural engineer’s software wants kg/m³: 145 × 16.018463 = 2322.7 kg/m³. Lightweight mix at 110 lb/ft³ converts to 1762.0 kg/m³ — a 24% dead-load saving the engineer can now quantify for the foundation design.
A third: shipping. A freight quote charges by dimensional weight, but the cargo is lead-acid batteries at 11.34 g/cm³. The logistics sheet wants lb/gal to check hazmat thresholds: 11.34 × 1000 ÷ 119.826 = 94.64 lb/gal. The density alone flags the shipment as far beyond typical liquid limits — the converter turned a chemistry number into a logistics decision.
The periodic table is a density story: osmium (22.59 g/cm³) and iridium (22.56) are the densest natural elements — a fist-sized lump of osmium weighs as much as a milk jug of water. Aerogels go the other way: 0.001 g/cm³, barely denser than air, yet solid enough to hold. The converter spans this entire range without blinking, because the factors are exact ratios, not approximations.
Oceanography runs on density differences of 0.1%: seawater at 1025 kg/m³ vs. fresh water at 1000 drives thermohaline circulation — the ocean conveyor belt that regulates climate. CTD instruments measure conductivity, temperature, and depth, then compute density to 0.01 kg/m³; converting those profiles between the kg/m³ of science and the lb/ft³ of offshore engineering is daily work on research vessels.
Aviation cares because fuel is sold by volume but burned by mass: jet fuel at 0.804 g/cm³ means 10,000 liters weighs 8,040 kg, and range calculations use the mass. Fuel farms measure density continuously to correct metered volumes to standard conditions — a 1% density error is a 1% payload error, which is a very expensive rounding.
Medicine uses density quietly: urine specific gravity (1.002–1.030) screens kidney function; bone densitometry tracks osteoporosis; and the famous Archimedes “Eureka” moment was a density test — the crown’s density would betray debased gold. Modern gold verification still starts with density: 19.32 g/cm³, non-negotiable.
Geology’s layered Earth is density-sorted: crust ~2.7, mantle ~4.5, core ~13 g/cm³. Seismic waves speed up in denser rock, and the whole model of Earth’s interior is an inversion of travel times into density. Converting those g/cm³ values to the kg/m³ of physics equations is the first line of every geophysics lecture.
Manufacturing quality control checks density to catch voids: a cast part that should be 7.85 g/cm³ but measures 7.6 has ~3% porosity — reject. Plastics compounders verify filler loading the same way. The converter’s four-decimal output matches the resolution of a good lab balance and graduated cylinder.
Even cooking is applied densitometry: a cup of flour weighs 120 g but a cup of honey weighs 340 g — volume measures lie, mass tells the truth, and density is the exchange rate. Serious bakers weigh everything; the density converter explains why the scale beats the cup.
One more pattern worth internalizing: density ratios are dimensionless and therefore unit-proof. Specific gravity 2.7 means the same in Tokyo and Texas. When a specification is safety-critical, quote the ratio alongside the converted value — it is the one number no unit confusion can corrupt. The widget prints it every time for exactly this reason.
Density converter: input value × (from-factor / to-factor), factors in kg/m³: g/cm³=1000, kg/m³=1, g/L=1, lb/ft³=16.018463, lb/gal(US)=119.826427. Water reference 1000 kg/m³; ratio = specific gravity; >1 sinks, <1 floats. Source: Sigma Calculator, Density Converter, https://sigmacalculator.net/math-calculators/density-converter/
Cite this page as: Density Converter, Sigma Calculator, https://sigmacalculator.net/math-calculators/density-converter/
Last updated: October 12, 2026