Oil Composition Calculator
Bulk Oil Properties
What Is the Oil Composition Calculator?
The Oil Composition Calculator is a technical tool that converts SARA weight inputs into estimated bulk properties. SARA stands for saturates, aromatics, resins, and asphaltenes. These four fractions represent broad groups of petroleum compounds with different densities, molecular weights, and hydrogen-to-carbon ratios.
Enter the weight percentage of each SARA fraction. The calculator normalizes the entries, applies fixed reference properties to each fraction, and estimates the oil’s average density, molecular weight, H/C ratio, volume composition, and mole composition. It also provides a short composition-based summary.
The tool helps users compare how lighter and heavier SARA fractions contribute to a combined oil sample. Its results are estimates based on fixed constants in the calculator, not measurements of the sample’s actual chemical properties.
How the Oil Composition Calculator Formula Works
The calculator begins by adding the four entered weights. It then divides each entry by that total. This automatically normalizes the composition when the entered values do not add up to exactly 100.
In this formula, wi is the entered weight for one SARA fraction. fi is its normalized mass fraction.
| SARA fraction | Molecular weight | Density | H/C ratio |
|---|---|---|---|
| Saturates | 400 g/mol | 0.85 g/cm³ | 2.0 |
| Aromatics | 350 g/mol | 0.95 g/cm³ | 1.2 |
| Resins | 800 g/mol | 1.05 g/cm³ | 1.1 |
| Asphaltenes | 1,500 g/mol | 1.20 g/cm³ | 1.0 |
The calculator uses the fixed values above as representative constants. It estimates each fraction’s relative volume by dividing its normalized mass fraction by density. Average density is the reciprocal of the combined relative volume.
It estimates relative moles by dividing each mass fraction by its molecular weight. Average molecular weight is the reciprocal of the total relative moles.
The average H/C ratio is mole-weighted. Fractions that contribute more calculated moles have a greater effect on this result.
For example, enter 60 for saturates, 25 for aromatics, 10 for resins, and 5 for asphaltenes. The total is 100, so the normalized fractions are 0.60, 0.25, 0.10, and 0.05. The calculator returns an average density of 0.904 g/cm³, an average molecular weight of 421 g/mol, and an average H/C ratio of 1.70.
The calculated volume shares are 63.8% saturates, 23.8% aromatics, 8.6% resins, and 3.8% asphaltenes. The mole shares are 63.2%, 30.1%, 5.3%, and 1.4%, respectively. Because neither asphaltenes exceed 10% nor saturates exceed 60%, the calculator selects its medium-grade summary.
How to Use the Oil Composition Calculator: Step by Step
- Enter the Saturates Weight (%) for the oil sample. The field is configured for values from 0 to 100 in increments of 0.1.
- Enter the Aromatics Weight (%). Use the measured or assumed value for the sample you are evaluating.
- Enter the Resins Weight (%). Leave the field blank only when you want the calculator to treat that fraction as zero.
- Enter the Asphaltenes Weight (%). Use a nonnegative value that reflects the same weight basis as the other entries.
- Select Calculate. The calculator adds the entries and normalizes them, so they do not need to total exactly 100.
- Review the bulk density, molecular weight, H/C ratio, SARA composition details, and plain-English summary. Select Reset to clear every input and hide the results.
The density result is shown to three decimal places. Molecular weight is shown as a whole number, while the H/C ratio is shown to two decimal places. Volume and mole shares are shown to one decimal place. If all fields are blank or the entered total is zero or less, the results remain hidden.
How to Read Your Oil Composition Calculator Results
Average Density
Average density estimates the mass per unit volume of the combined composition. Fractions with lower reference densities contribute more relative volume for the same mass. This calculator reports density in grams per cubic centimeter using an ideal additive-volume mixing rule.
Average Molecular Weight and H/C Ratio
Average molecular weight represents the estimated mass of one mole of the modeled mixture. The H/C result describes the calculated balance of hydrogen relative to carbon. Both values depend on the fixed molecular weight and H/C constants assigned to the four SARA groups.
Volume and Mole Percentages
Volume percentages adjust the normalized mass fractions for density. Mole percentages adjust them for molecular weight. A fraction can therefore have different weight, volume, and mole shares. Lower-density fractions tend to occupy more volume, while lower-molecular-weight fractions contribute more calculated moles for the same mass.
How the Summary Is Selected
The summary follows three coded conditions. If normalized asphaltenes are greater than 10%, it describes the sample as heavy and potentially viscous. Otherwise, if normalized saturates are greater than 60%, it describes the sample as light and saturate-rich. Every other composition receives the medium-grade summary. The thresholds are strict, so exactly 10% or 60% does not trigger those conditions.
Important Display and Calculation Limitations
In the detailed SARA output, the calculator formats each normalized mass fraction to one decimal place and then adds a “% Wt” label. It does not multiply that fraction by 100. An input that normalizes to 60% by weight may therefore appear as “0.6% Wt.” In that line, 0.6 should be read as a fraction equivalent to 60%.
The results use representative constants, not sample-specific laboratory measurements. Actual petroleum properties can vary with crude source, temperature, pressure, test method, fraction definitions, and detailed molecular composition. The summary is a simplified classification generated from only two composition thresholds. Do not treat it as a transport, refining, safety, or engineering recommendation.
Frequently Asked Questions
What does an Oil Composition Calculator calculate?
It calculates estimated bulk properties from saturates, aromatics, resins, and asphaltenes weight inputs. The displayed results include average density, average molecular weight, average H/C ratio, volume percentages, mole percentages, normalized weight fractions, and a short summary selected from the calculated composition.
Do SARA percentages have to add up to 100?
No. The calculator automatically divides each entered value by the total of all four entries. For example, inputs of 30, 15, 4, and 1 are treated in the same proportions as 60, 30, 8, and 2. Only the relative values affect the result.
What happens when a SARA field is left blank?
A blank field is treated as zero because the calculator converts missing or nonnumeric input to zero. It can still calculate when at least one entered value makes the total greater than zero. When the total is zero or less, the calculator hides the results and performs no displayed calculation.
How is average oil density calculated?
The calculator divides each normalized mass fraction by its assigned density, adds the resulting relative volumes, and takes the reciprocal. It assumes the fraction volumes are additive. The assigned densities are 0.85, 0.95, 1.05, and 1.20 g/cm³ for the four SARA fractions.
Why are weight, volume, and mole percentages different?
They use different measurement bases. Weight composition compares mass, volume composition adjusts each fraction for density, and mole composition adjusts it for molecular weight. A light or low-molecular-weight fraction may therefore have a larger volume or mole share than its original contribution by weight.
How accurate is the Oil Composition Calculator?
Its arithmetic follows the formulas and constants built into the tool, but the output is an estimate. Each SARA group is represented by one fixed density, molecular weight, and H/C ratio. Real samples contain many compounds, so measured laboratory properties may differ from the calculated values.
Why does the displayed weight result look too small?
The detailed output displays the normalized mass fraction with a percent label but does not convert the fraction to a percentage. A displayed weight value of 0.6 represents a fraction of 0.6, which is equivalent to 60%. The volume and mole values are multiplied by 100 before display.