Density Converter

Density is mass divided by volume (ρ = m ÷ V). The converter routes everything through kg/m³:

result = value × factor(from) ÷ factor(to)

• 1 kg/m³ = 1 (SI base)
• 1 g/cm³ = 1000 kg/m³ exactly (1 g = 10⁻³ kg, 1 cm³ = 10⁻⁶ m³). It is also equal to 1 g/mL and 1 kg/L.
• 1 lb/ft³ = 0.45359237 kg ÷ 0.028316846592 m³ = 16.01846337 kg/m³

The pound and the foot are both defined exactly in metric terms (since 1959), so the lb/ft³ factor is exact to the digits shown.

Reference densities for sanity checks:

• Fresh water at about 4 °C: 1000 kg/m³ = 1 g/cm³ = 62.43 lb/ft³ (at 20 °C it is 998.2 kg/m³)
• Seawater: about 1025 kg/m³
• Normal-weight concrete: 2300–2400 kg/m³ (about 145–150 lb/ft³)
• Structural steel: 7850 kg/m³ = 7.85 g/cm³ (about 490 lb/ft³)
• Aluminium: 2700 kg/m³
• Dry air at sea level and 15 °C: 1.225 kg/m³

Specific gravity. Many datasheets give specific gravity (SG) instead of density — the ratio to water. Because water is close to 1 g/cm³, an SG of 2.7 means about 2.7 g/cm³, which you can then convert here. Strictly the reference temperature matters, but for most practical estimates the difference is under 0.3%.

Bulk versus true density. Sand, gravel, flour and grain have a bulk density that includes the air between particles, often 30–45% lower than the density of the solid material itself. Use bulk density for ordering loose materials by volume, and true (particle) density for buoyancy or porosity work.

Temperature and pressure. Gases are especially sensitive: halve the absolute pressure and the density halves. Liquids change less, but petrol, for instance, expands about 0.1% per °C, which is why fuel is sometimes sold temperature-compensated. The converter does not adjust for any of this — it only changes units.

Textbook water value in SI

Inputs: 62.4, From lb/ft³, To kg/m³

US textbooks often give water as 62.4 lb/ft³. Enter 62.4 with lb/ft³ → kg/m³; the tool multiplies by 16.01846337.

Result: 999.5521143

About 1000 kg/m³ — the familiar SI value. The small gap is because 62.4 is itself rounded.

Concrete for a US contractor

Inputs: 2400, From kg/m³, To lb/ft³

Enter 2400 with kg/m³ → lb/ft³: 2400 ÷ 16.01846337.

Result: 149.8271054

The familiar "150 pcf" figure used in US structural design.

Steel density for a weight estimate

Inputs: 7.85, From g/cm³, To lb/ft³

Enter 7.85 with g/cm³ → lb/ft³. The tool goes 7.85 × 1000 = 7850 kg/m³, then ÷ 16.01846337.

Result: 490.0594906

A 2 ft³ steel block therefore weighs about 980 lb.

Is 1 g/cm³ the same as 1000 kg/m³?

Yes, exactly. A cube 1 m on each side holds one million cm³, and one million grams is 1000 kg.

Why is water 62.4 lb/ft³ in some books and 62.43 in others?

They are rounding the same quantity differently, and sometimes quoting different temperatures. At 4 °C water is 999.97 kg/m³, which converts to about 62.43 lb/ft³.

How do I convert specific gravity to density?

Multiply SG by the density of water: SG × 1000 kg/m³, or simply read SG as g/cm³.

Can I convert lb/gal or kg/L?

kg/L equals g/cm³, so use that option. US lb/gal is not built in; multiply it by 119.826 to get kg/m³.

Does the converter account for temperature?

No. It converts units only. Use a density value measured at the temperature you care about.

How do I estimate the weight of a sheet of steel?

Multiply length × width × thickness in metres to get m³, then multiply by 7850 kg/m³. A 2 m × 1 m × 0.005 m plate is 0.01 m³, so about 78.5 kg. If your drawing is in inches, convert the volume to ft³ and use about 490 lb/ft³ instead.

What density should I use for concrete?

About 2400 kg/m³ for normal-weight reinforced concrete is a common design assumption; lightweight mixes can be 1400–1900 kg/m³. Check your supplier’s mix sheet.