ISO 17507-1:2025
MNc method
The MNc method in ISO 17507-1:2025 calculates methane number from gas composition using the standard's predefined ternary systems. This implementation follows that calculation model and finds a distribution that meets the standard's limits.
Calculation model
The combustible composition is distributed among selected ternary systems. A methane number is calculated for each system, and the final MNc methane number combines those values according to the systems' shares. Inert components are included through the correction defined by the standard.
The implementation follows the standard's component handling, normalization, method limits, ternary-system data, and inert correction. Compositions entered by volume, mole, or mass are converted according to ISO 14912:2025 and then prepared for the MNc method.
Input guidance
A grouped analysis value does not identify an individual chemical component. Enter the complete grouped value as the component shown below.
| Reported as | Enter as |
|---|---|
| Butanes | n-Butane (C4H10) |
| Butadiene | 1,3-Butadiene (C4H6) |
| Butylene | 1-Butene (C4H8) |
| Pentanes | n-Pentane (C5H12) |
| Hexanes+ | n-Hexane (C6H14) |
For the MNc method, these substitutions normally have little effect because gas volume and amount fractions are very similar under the applicable conditions, and isomers within each group have the same molar mass. Hexanes+ requires more care for mass input because it may contain heavier hydrocarbons.
Distribution across ternary systems
The same composition can have more than one valid distribution across the selected ternary systems. The calculator applies several optimization methods and selects the result with the best agreement between the systems' methane numbers. The reported system shares show the distribution used for the result.
Spread is the difference between the highest and lowest methane numbers among the selected ternary systems used in the weighted result. Read it alongside each system's share and methane number. A system with a small share can increase the spread while having little effect on the final weighted result. When the systems with differing methane numbers represent substantial shares of the composition, a large spread is a reason to interpret the weighted result with caution.
Implementation and validation
This calculator implements the MNc method described in ISO 17507-1:2025, including its equations, component rules, and ternary systems. It closely reproduces the published worked examples. For some Annex A.10 mixtures, the selected ternary systems agree closely even though the final MNc differs from the reference value. The validation page shows the results and differences for each comparison.