Sources and scope for this page: ISO 3448:1992, covering the ISO VG grade definitions; and ASTM D445-23, covering the measurement method behind the kinematic values (one more source is tabulated below). No independent source check is recorded for this page: the content rests on the sources listed and on the working shown on the page. Full sources, values and limits on this page.
Page last changed 2026-10-19 · based on ISO 3448:1992
Quick Answer
Viscosity of Common Fluids
| Fluid[2] | Temperature °C[2] | Dynamic viscosity mPa·s[2] | Kinematic viscosity mm²/s (cSt)[1] | Density kg/m³[2] | Note[2] |
|---|---|---|---|---|---|
| Water (0 °C) # | 0 | 1.792 | 1.792 | 1000 | Water thickens markedly as it cools |
| Water (10 °C) # | 10 | 1.307 | 1.307 | 1000 | |
| Water (20 °C) # | 20 | 1.002 | 1.004 | 998 | The reference point where water's viscosity is about 1 mPa·s |
| Water (40 °C) # | 40 | 0.653 | 0.6583 | 992 | |
| Water (60 °C) # | 60 | 0.467 | 0.4751 | 983 | |
| Water (80 °C) # | 80 | 0.355 | 0.3652 | 972 | |
| Water (100 °C) # | 100 | 0.282 | 0.2944 | 958 | At boiling point — viscosity has fallen by a factor of 6.4 |
| Sea water (3.5%, 20 °C) # | 20 | 1.07 | 1.044 | 1025 | Slightly more viscous than fresh water |
| Ethanol (20 °C) # | 20 | 1.1 | 1.394 | 789 | Similar to water despite much lower density |
| Methanol (20 °C) # | 20 | 0.59 | 0.7449 | 792 | Less viscous than ethanol |
| Ethylene glycol (20 °C) # | 20 | 16.1 | 14.47 | 1113 | 16 times water — a real pumping cost in antifreeze loops |
| Glycerol (20 °C) # | 20 | 1412 | 1120 | 1261 | Extremely viscous; about 1 400 times water |
| Mercury (20 °C) # | 20 | 1.55 | 0.1145 | 13534 | Low viscosity despite very high density — hence a low kinematic value |
| Kerosene (20 °C) # | 20 | 1.64 | 2.025 | 810 | |
| Gasoline (20 °C) # | 20 | 0.6 | 0.8108 | 740 | Low viscosity, low flash point |
| Diesel fuel (20 °C) # | 20 | 3 | 3.529 | 850 | Varies with grade; winter diesel is thinner |
| Hydraulic oil ISO VG 46 (40 °C) # | 40 | 40.3 | 46 | 876 | The ISO VG grade number is 46 cSt at 40 °C by definition — the dynamic value is that times density |
| Hydraulic oil ISO VG 46 (100 °C) # | 100 | 5.71 | 6.798 | 840 | A viscosity index of about 100, which is the conventional hydraulic oil target |
| Engine oil SAE 30 (40 °C) # | 40 | 88 | 100 | 880 | Monograde reference; the grade is set kinematically |
| Engine oil SAE 15W-40 (40 °C) # | 40 | 91.9 | 105 | 875 | The W number rates cold behaviour, the second number hot |
| Engine oil SAE 15W-40 (100 °C) # | 100 | 12.2 | 14.52 | 840 | From a published kinematic value of 14.5 cSt at 100 °C |
| Honey (20 °C) # | 20 | 1e+04 | 7042 | 1420 | Roughly 10 000 times water in dynamic viscosity |
| Air (20 °C) # | 20 | 0.0182 | 15.1 | 1.205 | Gases are two to five orders of magnitude less viscous than liquids |
| Air (100 °C) # | 100 | 0.0218 | 23.04 | 0.946 | Gas viscosity rises with temperature — the opposite of liquids |
| Carbon dioxide (20 °C) # | 20 | 0.0147 | 7.436 | 1.977 | |
| Steam, saturated (100 °C) # | 100 | 0.0123 | 20.57 | 0.598 |
Dynamic viscosity (mPa·s, also called the centipoise) is the fluid's internal resistance to shear. Kinematic viscosity (mm²/s, also called the centistoke) is the dynamic value divided by density, and is what oil grades are specified in — an ISO VG 46 oil has a kinematic viscosity of 46 cSt at 40 °C by definition. Because the conversion needs density, a fluid with a high density but a low dynamic viscosity, such as mercury, has an unexpectedly low kinematic viscosity. The same fluid appears more than once at different temperatures, because the temperature dependence is larger than the difference between many fluids.
Dynamic vs Kinematic — Which Number You Need
The two viscosity measures answer different questions, and using the wrong one is a common source of a factor-of-a-thousand error.
Dynamic viscosity (µ, mPa·s or cP) is a force-per-area quantity. It is what appears in the Reynolds number, in pressure-drop equations, in bearing and lubrication calculations, and in anything involving shear stress. Its SI unit is the pascal-second, so mPa·s is 0.001 Pa·s — and 1 mPa·s equals 1 centipoise exactly, which is why the older unit survives so completely.
Kinematic viscosity (ν, mm²/s or cSt) is dynamic viscosity divided by density. It is what appears in gravity-driven flow, in pipe-sizing nomograms, and in oil grading. Its SI unit is m²/s, which is far too large for practical fluids, so mm²/s — identical to the centistoke — is the working unit.
The relationship is ν = µ/ρ. Because density is in the denominator, two fluids with the same dynamic viscosity can have very different kinematic viscosities: mercury at 1.55 mPa·s has a kinematic viscosity of only 0.115 cSt, because its density is 13 534 kg/m³. Conversely, ISO VG oil grades are specified kinematically, so an ISO VG 46 oil must measure 46 cSt at 40 °C regardless of its additive package.
Why Temperature Changes Everything
Viscosity is far more temperature-sensitive than almost any other fluid property, and the sensitivity runs in opposite directions for liquids and gases.
Liquids thin as they heat. Water drops from 1.792 mPa·s at 0 °C to 0.282 at 100 °C — a factor of 6.4. Engine oil changes far more: an SAE 15W-40 goes from about 105 mPa·s at 40 °C to 14.5 at 100 °C, and at −20 °C it would be several thousand. This is why multi-grade oils exist and why the viscosity index is a specification in its own right — it describes how flat the viscosity-temperature curve is.
Gases thicken as they heat. Air rises from 0.0182 mPa·s at 20 °C to 0.0218 at 100 °C, an increase of 20%. The mechanism is different: in a liquid, molecules are close together and heating loosens the bonds that resist sliding, while in a gas momentum transfer between molecules increases with their speed. The practical consequence is that hot air is harder to push through a duct than cold air, even though its density is lower — an effect that surprises people sizing exhaust systems.
For any calculation where viscosity appears, use the value at the operating temperature, not at 20 °C. A pressure-drop calculation done with room-temperature viscosity for a fluid at 80 °C can be out by a factor of three or more.
Frequently Asked Questions
- What is the viscosity of water?
- 1.002 mPa·s at 20 °C, which is close enough to 1 that the millipascal-second and the centipoise are treated as the same unit. Water's viscosity is strongly temperature dependent: 1.792 mPa·s at 0 °C, 1.002 at 20 °C, 0.653 at 40 °C and 0.282 at 100 °C. Below about 0 °C it rises steeply, which is why cold water is noticeably harder to pump.
- What is the difference between cSt and cP?
- The centistoke (cSt) is kinematic viscosity in mm²/s; the centipoise (cP) is dynamic viscosity in mPa·s. They differ by the fluid's density: cSt = cP ÷ (density in g/cm³). For water, whose density is about 1 g/cm³, the two numbers coincide — which is why they are so often confused. For mercury, at 13.5 g/cm³, a 1.55 cP dynamic viscosity corresponds to only 0.115 cSt.
- What does the ISO VG number mean?
- It is the kinematic viscosity in cSt at 40 °C, by definition — an ISO VG 46 oil measures 46 cSt at 40 °C, an ISO VG 32 measures 32. The grades follow a standard preferred-number series with ±10% tolerance. The number says nothing about how the oil behaves at other temperatures, which is what the viscosity index describes.
- Why do gases get more viscous when heated?
- Because gas viscosity comes from momentum transfer between molecules rather than from intermolecular attraction. Heating makes the molecules move faster, so they transfer momentum more effectively across a shear layer, and viscosity rises. Air goes from 0.0182 mPa·s at 20 °C to 0.0218 at 100 °C. Liquids behave the opposite way, because heating weakens the intermolecular bonds that resist sliding.
- Do I use dynamic or kinematic viscosity for pressure drop?
- Dynamic viscosity, in the Reynolds number and in the Darcy-Weisbach friction factor. Kinematic viscosity appears in gravity-driven and open-channel work, and in the pipe-sizing nomograms some handbooks publish. If a formula asks for viscosity without specifying, check its units: Pa·s or cP means dynamic, m²/s or cSt means kinematic. Using the wrong one is a common source of large errors.
Related
Value Sources
References and calculation methods used for this page are listed below. Numbered markers connect table columns where present. A reference listing does not itself establish that every value has been independently checked.
| # | Source | Type | Revision / method |
|---|---|---|---|
| [1] | Kinematic viscosity computed from dynamic viscosity and density | derived | ν (mm²/s) = µ (mPa·s) ÷ ρ (kg/m³) × 1000, which is the standard ν = µ/ρ relationship with the units reconciled. Anchored by known-value checks — water at 20 °C must come out at 1.004 cSt and ISO VG 46 oil at exactly 46 cSt at 40 °C, since that is the definition of the grade. |
| [2] | Published viscosity data for common fluids | reference | compilations as published 2024–2026 |
Data Sources
| Standard | Revision | What it covers on this page |
|---|---|---|
| ISO 3448 — Industrial lubricants, classification of viscosity grades | ISO 3448:1992 | the ISO VG grade definitions |
| ASTM D445 — Kinematic Viscosity of Transparent and Opaque Liquids | ASTM D445-23 | the measurement method behind the kinematic values |
| NIST reference data for water and air viscosity | NIST Standard Reference Database 69 and IAPWS formulations, 2023 | the water and air values across temperature |
Verification scope
No page-specific independent source review is recorded here. The listed references and formulas explain the basis of the compilation; automated consistency checks do not verify the original sources or establish product conformity.
Derived values — the following values on this page are calculated, not taken directly from the standard:
| Value | How it is derived |
|---|---|
| Kinematic viscosity in mm²/s (cSt) | ν = µ/ρ with µ in mPa·s and ρ in kg/m³, multiplied by 1000 to give mm²/s. Anchored by two known-value checks that would fail if the reference were misapplied: water at 20 °C must be 1.004 cSt and ISO VG 46 oil must be exactly 46 cSt at 40 °C. |
Values are typical published figures at the stated temperature. Viscosity is the most temperature-sensitive property in this chart — a factor of two or more over a 40 °C change is normal for oils — so always use the value at the operating temperature. Non-Newtonian fluids such as grease, slurry and many food products have no single viscosity at all; their apparent viscosity depends on shear rate and they are not represented here.
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