A fluid's headline properties are its density (mass per volume) and its viscosity (resistance to
flow). Viscosity comes in two flavours: dynamic (μ, in mPa·s or centipoise) and kinematic
(ν, in mm²/s or centistokes) — related by density, ν = μ/ρ. Every liquid thins as it warms, so a
single viscosity number only means something with a temperature attached. This tool models that curve from two
reference points and lets you compare fluids on one chart.
Hydraulic ISO VG 46 oil is defined as 46 cSt at 40°C — that's what the grade number means. Heat it to 100°C and it thins to about 6.8 cSt, over six times runnier. Water at 40°C is only 0.66 cSt, so the oil is roughly 70× thicker.
The viscosity index captures how flat that curve is: a multigrade 10W-40 keeps its thickness across a wider temperature range than a monograde SAE 30, even when both start near 100 cSt at 40°C.
Pump and pressure-drop calculations usually want kinematic (ν); force and shear calculations want
dynamic (μ). This tool shows both at your chosen temperature. Convert with μ = ν·ρ.
The number is the oil's nominal kinematic viscosity in centistokes at 40°C, ±10%. So ISO VG 46 sits between roughly 41 and 51 cSt at 40°C. SAE grades work differently and are measured at different temperatures.
It's fitted through two reference points with a standard viscosity–temperature relation, so it's good between and near them and rougher at the extremes. It ignores additives, shear thinning and phase changes. Use it for intuition and quick estimates, not for specification.
Specific gravity (density relative to water) tells you whether a fluid floats or sinks and helps convert between mass and volume. Most oils and fuels are lighter than water (SG < 1); glycerine and mercury are heavier.