Viscosity-temperature calculator
Oil Viscosity vs. Temperature Chart
Enter two known kinematic viscosities for the same oil, then calculate viscosity at any temperature between them.
Calculated curve
Calculated Oil Viscosity vs. Temperature
The Y axis is logarithmic so large viscosity changes remain readable across the measured interval.
Move a pointer near the curve, tap near a point, or focus the graph and use the left/right arrow keys to inspect values.
Industrial lubricant reference
ISO VG Oil Viscosity Reference
A limited set of commonly encountered ISO viscosity grades, referenced at 40°C.
Search by ISO VG designation or viscosity. The limits shown are the ISO 3448 classification band around the midpoint; they are not SAE equivalents or lubricant approvals.
No included ISO viscosity grade matches that search. Clear the search or use the calculator above with your oil’s measured data.
Scroll horizontally to view additional columns and vertically to view additional rows. Column headers remain visible while scrolling.
| Kinematic viscosity at 40°C | Reference temperature | Classification scope | Copy | |||
|---|---|---|---|---|---|---|
| ISO VG 22 | 22 | 19.8 | 24.2 | 40°C | Industrial liquid lubricant | |
| ISO VG 32 | 32 | 28.8 | 35.2 | 40°C | Industrial liquid lubricant | |
| ISO VG 46 | 46 | 41.4 | 50.6 | 40°C | Industrial liquid lubricant | |
| ISO VG 68 | 68 | 61.2 | 74.8 | 40°C | Industrial liquid lubricant | |
| ISO VG 100 | 100 | 90 | 110 | 40°C | Industrial liquid lubricant | |
| ISO VG 150 | 150 | 135 | 165 | 40°C | Industrial liquid lubricant | |
| ISO VG 220 | 220 | 198 | 242 | 40°C | Industrial liquid lubricant | |
| ISO VG 320 | 320 | 288 | 352 | 40°C | Industrial liquid lubricant | |
| ISO VG 460 | 460 | 414 | 506 | 40°C | Industrial liquid lubricant | |
| ISO VG 680 | 680 | 612 | 748 | 40°C | Industrial liquid lubricant | |
ISO VG identifies an industrial lubricant viscosity class at 40°C. It does not define additive chemistry, base oil, OEM approval, viscosity index, or a complete viscosity-temperature curve.
How to Read an Oil Viscosity Chart
Temperature is on the horizontal axis and kinematic viscosity is on the vertical axis. For a typical petroleum lubricant, the curve slopes downward because the oil becomes less viscous as temperature rises. This page uses a logarithmic viscosity axis so the curve remains readable even when viscosity changes by a large factor.
- cSt
- Centistokes, numerically equal to mm²/s for kinematic viscosity.
- Measured points
- The two temperature-viscosity pairs that define the ASTM D341 relationship for the specific oil.
- Interpolation
- A calculation between the two known temperatures. This tool intentionally disables extrapolation.
ISO VG vs. SAE Engine Oil vs. SAE Gear Oil
These are different classification systems and should not be treated as exact conversion scales. ISO 3448 classifies industrial liquid lubricants by kinematic viscosity at 40°C. SAE J300 classifies engine oils using multiple rheological requirements, including low-temperature and high-temperature criteria.
ISO VG
Use for industrial lubricant viscosity classification. The grade number is tied to a midpoint kinematic viscosity at 40°C.
SAE engine oil
Use SAE J300 for engine-oil rheological classification. A label such as 5W-30 is not a direct cSt conversion.
SAE gear oil
Automotive gear-oil viscosity grades use a different SAE system and application context from SAE engine oils.
Do not substitute oils solely because two grade labels appear close on a cross-reference chart. Confirm the equipment manufacturer’s viscosity, chemistry, performance, and approval requirements.
How Temperature Changes Oil Viscosity
ASTM D341 linearizes petroleum-oil viscosity-temperature behavior using a transformed viscosity value and absolute temperature. Two known viscosity-temperature observations determine constants for the curve, after which viscosity can be calculated at another temperature within the usable range.
Viscosity index is a separate concept: it describes how strongly an oil’s kinematic viscosity changes with temperature. A higher viscosity index generally means less viscosity change over temperature, but viscosity index by itself does not replace the actual measured viscosity values needed for this curve.
T is absolute temperature in kelvin; A and B are solved from the two known points. The D341 correction terms are applied in the calculator for low-viscosity accuracy.
Worked Viscosity-Temperature Example
70.0 cSt at 40°C and 10.0 cSt at 100°C
Known values: ν₄₀ = 70.0 cSt and ν₁₀₀ = 10.0 cSt.
Target: Calculate viscosity at 70°C.
ASTM D341 checkpoint: A ≈ 8.609 and B ≈ 3.342, giving ν₇₀ ≈ 22.3 cSt.
Sanity check: 22.3 cSt lies between 70.0 and 10.0 cSt and decreases with increasing temperature. This is interpolation, not an equipment-specific lubricant approval.
Choosing the Right Oil Viscosity
- Start with the equipment manufacturer’s lubricant specification. Required viscosity windows, oil type, additive system, and approvals take precedence over generic charts.
- Use the actual operating temperature. A nominal ISO VG value at 40°C does not tell you the exact viscosity at a bearing, gearbox, pump, or hydraulic component operating at another temperature.
- Use product-specific measured data. Enter the kinematic viscosities from the lubricant technical data sheet or laboratory results.
- Check cold-start and hot-running limits separately. An oil can be suitable at one operating condition and unsuitable at another.
- Confirm the complete lubricant requirement. Similar viscosity does not prove compatibility, additive performance, or OEM approval.
Common Oil Viscosity Mistakes
- Treating cP and cSt as interchangeable. Dynamic viscosity and kinematic viscosity are different quantities; density is required to convert between them.
- Assuming ISO VG defines the entire temperature curve. Two oils in the same ISO VG class can have different viscosity-temperature behavior.
- Reading SAE 5W-30 as “5 cSt cold and 30 cSt hot.” SAE grade numbers are classification labels, not direct cSt values.
- Extrapolating far beyond measured points. Small measurement errors can produce large errors outside the known range; this tool therefore limits calculations to interpolation.
- Ignoring lubricant condition. Oxidation, contamination, shear, wax formation, phase behavior, and additive effects can make real oil depart from a simple viscosity-temperature model.
Source, Method, and Data Limitations
Source checked September 4, 2026 · Publisher: Turn2Engineering · Calculated curve values are derived from user inputs.
The calculation follows ASTM D341’s current viscosity-temperature equation framework for petroleum oils and liquid hydrocarbons. The ISO VG table is intentionally limited to commonly encountered grades and is not offered as a standards-table download. The displayed ranges follow the ISO VG ±10% classification band at 40°C for the listed grades.
- ASTM D341-20(2025) — Standard Practice for Viscosity-Temperature Equations and Charts for Liquid Petroleum or Hydrocarbon ProductsControlling calculation method; Section 5 equation framework and example. ASTM material is copyrighted and is not reproduced as a complete standard or chart.
- ISO 3448:1992 — Industrial liquid lubricants — ISO viscosity classificationControls ISO VG classification scope. The edition was confirmed current by ISO; only a limited reference subset is displayed here.
- SAE International — J300_202405 Engine Oil Viscosity ClassificationOfficial SAE scope used only to distinguish engine-oil rheological classification from ISO VG. Detailed SAE limits are not reproduced on this page.
- ASTM D2270-24 — Standard Practice for Calculating Viscosity Index from Kinematic Viscosity at 40°C and 100°CSupports viscosity-index context and the conventional 40°C / 100°C measurement pair; this page does not calculate VI.
Dataset and Source-Check Details
- Dataset label
- T2E Oil Viscosity Reference & D341 Curve — source-checked 2026-09-04
- Curve source
- ASTM D341 formulation; values calculated from the user’s two measured points
- Curve range
- Interpolation only between the two entered temperatures
- Viscosity units
- cSt, numerically equal to mm²/s
- ISO VG reference
- Limited common-grade subset at 40°C; no bulk standards-derived CSV
- Rights status
- Standards are copyrighted; this page uses limited reference facts and independently calculated outputs
- Known exclusions
- No OEM approval, lubricant chemistry, dynamic-viscosity conversion, VI calculation, or extrapolation
- Application rule
- Equipment-manufacturer lubricant requirements take precedence
Oil Viscosity Chart FAQs
The meaning depends on the grading system: ISO VG, SAE engine-oil, and SAE gear-oil numbers are different classifications and cannot be interpreted as one common numeric scale.
No. ISO VG 46 is an industrial viscosity classification referenced at 40°C; the oil’s actual kinematic viscosity changes substantially with temperature.
Only rough viscosity comparisons are possible in some contexts; the standards use different tests and application requirements, so a cross-reference is not an interchange approval.
cSt measures kinematic viscosity while cP measures dynamic viscosity; converting between them requires the fluid density at the relevant condition.
Higher temperature generally increases molecular mobility and reduces a liquid oil’s resistance to flow, although the magnitude of the change depends on the specific lubricant.
Use the Actual Oil Data for Engineering Decisions
An oil grade is a classification, not a complete temperature-viscosity curve. For equipment checks, use the lubricant’s measured or published kinematic viscosities, interpolate only within a defensible range, and compare the resulting operating viscosity with the equipment manufacturer’s requirements.