This density converter translates density between kg/m³, g/cm³, lb/ft³, lb per US gallon and specific gravity — the units labs, shipping desks and brewers argue in.

Specific gravity is density in disguise: SG = density ÷ 1,000 kg/m³ (water at 4 °C). Hydrometers, brewers and battery testers all read SG because it’s density with the arithmetic pre-done.

Water at 1,000 kg/m³ Is the Rosetta Stone

Every density unit converts through water’s round SI value. Computing density from mass and volume is our Density Calculator. Part of our Conversion Calculators collection.

Anchor Conversions (Verified)

  • Water: 1,000 kg/m³ = 1.000 g/cm³ = 62.43 lb/ft³ = 8.345 lb/gal = SG 1.000 — the defaults and the reference for everything below
  • Seawater ≈ 1,025 kg/m³ (SG 1.025) — the 2.5% that floats you noticeably better and sinks eggs on cue
  • Gasoline ≈ 737 kg/m³ (6.15 lb/gal) — fuel is sold by volume but burned by mass, so density swings move real energy per gallon
  • Gold 19,320 kg/m³ (SG 19.3) — the Archimedes crown test, still the fastest sanity check in the pawn business

Where Density Units Collide

  • Labs think g/cm³ (= g/mL); engineers SI kg/m³; US industry lb/ft³ and lb/gal.
  • API gravity inverts SG for petroleum (lighter = higher degrees) — a dialect this converter leaves to the oil patch.
  • Temperature moves density (water peaks at 4 °C) — reference temperatures ride along with precise tables.
  • Air at sea level ≈ 1.225 kg/m³ — three orders below liquids, the scale intuition for aerostatics.

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Frequently Asked Questions

How do I convert kg/m³ to g/cm³?

Divide by 1,000: 1,000 kg/m³ = 1 g/cm³. The SI and CGS densities of water are both “one” in their home systems — a deliberate kindness of the metric definitions. This converter covers lb/ft³, lb/gal and specific gravity as well.

What is specific gravity?

The ratio of a substance’s density to water’s (at 4 °C): SG = density ÷ 1,000 kg/m³. It’s unitless, hydrometer-friendly, and rules brewing (wort sugars), battery electrolyte testing and urine analysis. SG 1.025 seawater is 2.5% denser than fresh water.

How many pounds does a gallon of water weigh?

8.345 lb at reference conditions — the “a pint’s a pound” rhyme approximates it (a US pint of water ≈ 1.04 lb). Diesel ≈ 7.0 lb/gal, gasoline ≈ 6.15 — vehicle weight math runs on these figures.

Why does density change with temperature?

Thermal expansion changes volume while mass stands still; most liquids thin as they warm (water anomalously densest at 4 °C). Precise work states the reference temperature — custody-transfer oil tables correct volumes to 15 °C or 60 °F for this reason.

What is the density of air?

≈ 1.225 kg/m³ at sea level, 15 °C (0.001225 g/cm³, SG ≈ 0.0012). It halves by ~18,000 ft — aviation performance, turbo sizing and HVAC all read density altitude off this decline.

Is this density converter free?

Yes — free, instant, no sign-up.