Density and viscosity both describe materials, but they measure different things and appear in different units. The density converter calculator converts mass per volume among kilograms per cubic meter, grams per cubic centimeter, and pounds per cubic foot. The viscosity converter calculator converts a fluid’s resistance to flow among pascal-second, poise, centipoise, and millipascal-second. The two meet when kinematic viscosity is involved, which is why the viscosity page links its density converter.
What each calculator does
The density converter calculator converts a nonnegative density value among kg/m³, g/cm³, and lb/ft³ using exact definition-based factors, with kilograms per cubic meter as the base: 1 g/cm³ equals 1,000 kg/m³ and 1 lb/ft³ equals 16.01846337396014 kg/m³. Its worked example converts 0.8 g/cm³ to 800 kg/m³, then to 49.942368 lb/ft³. The page grounds the quantity as density = mass ÷ volume, notes that water is roughly 1,000 kg/m³ and air close to 1.2 kg/m³ near common conditions, and warns that bulk materials include air spaces between particles, so bulk density can be far lower than particle density.
The viscosity converter calculator converts nonnegative dynamic viscosity among pascal-second, poise, centipoise, and millipascal-second through Pa·s: 1 P = 0.1 Pa·s, and cP and mPa·s share the factor 0.001 Pa·s, so equal numeric values in those two units represent the same viscosity. Its worked example converts 0.75 Pa·s to 750.0000 cP, with the all-units list reporting 0.750000 Pa·s, 7.5000 P, 750.0000 cP, and 750.0000 mPa·s. The page defines dynamic viscosity through the Newtonian shear relation (shear stress equals viscosity times velocity gradient) and notes water is close to 1 cP near room temperature.
Side-by-side
| Density converter | Viscosity converter | |
|---|---|---|
| Physical quantity | Mass per volume | Resistance to flow (dynamic viscosity) |
| Defining formula | ρ = m ÷ V | τ = μ × du ÷ dy |
| Units converted | kg/m³, g/cm³, lb/ft³ | Pa·s, P, cP, mPa·s |
| Base unit | kg/m³ (factors 1, 1,000, 16.01846337396014) | Pa·s (factors 1, 0.1, 0.001, 0.001) |
| Key relationship | 1 g/cm³ = 1,000 kg/m³ | 1 cP = 1 mPa·s; 1 Pa·s = 10 P = 1,000 cP |
| Common intersection | Needed to convert kinematic to dynamic viscosity | Kinematic viscosity = dynamic ÷ density |
When to use which
Use the density converter when you are comparing how much mass sits in a volume: fluids, soils, aggregates, woods, plastics, gases, and building materials written in different unit systems. The page points out that kg/m³ is the safest unit for engineering calculations because it works with SI force, pressure, buoyancy, and flow formulas, while g/cm³ gives compact lab numbers and lb/ft³ fits US construction, shipping, and bulk-material specifications.
Use the viscosity converter when the question is how a fluid flows: lubricants, coatings, food fluids, paints, and laboratory data sheets quoted in Pa·s, poise, centipoise, or millipascal-second. The page notes that centipoise is popular in industry because common liquids fall into readable ranges and millipascal-second is numerically identical while fitting SI-prefix style, and that a laboratory may report 500 mPa·s instead of 500 cP.
Limits and disclaimer
Both converters change unit labels only; they do not compute mass, volume, flow rate, pressure drop, or temperature correction. Density is mass per volume, not weight, and the density page notes that in everyday US usage pounds may mean mass or force depending on context, while its lb/ft³ factor treats pounds as the customary mass unit. Viscosity comparisons must match temperature, shear rate, spindle, method, and sample history, since many real fluids are non-Newtonian — paint, ketchup, polymer solutions, and slurries can appear thinner or thicker depending on how they are sheared. Both pages respect significant figures: the converters print fixed decimals, but a field-measured value may not justify that many digits, so round the final result to match the precision of the original measurement.