onlineflow is an online calculator for unit conversion of mass, molar and volume flows. These calculations are often tedious, error-prone and in sum very time-consuming. The online calculator offers remedy: With onlineflow all converting calculations can be done quickly, properly and well documentated.

General information about the user interface

Please fill in all input boxes. Output boxes in grey ('output') are only for information and are locked.

Results are displayed after all necessary data has been entered. Otherwise the output-fields display 'output'.

Data from a selection list is sent immediately to the system and the page will be updated. Data from selection lists are linked with each other, possible selections from lists will be updated as well. Thus only possible combinations can be selected. If you wish to reset your selection, please select '-' from the selection list. If you wish to reset all lists, you can reset the whole page by clicking 'calc' in the title-section.

The field 'Mixture'

In case mass, molar or standardized volume flows have to be converted molar mass of the mixture is needed. This field allows you to enter the mixture composition. Please enter the complete mixture. Flows will not be converted unless ALL fields are filled with the name and parts of gases. Please select the correct number of gases by the selection box 'Elements' at the end of the field 'Mixture'. At the moment mixture composition of up to 7 elements is possible.

Please check that the sum of parts for of your mixture composition is exactly 1. Otherwise it is not possible to start the calculation.

Predefined compositions

The following mixtures have been predefined:

Air: N2 0.78084, O2 0.20942, Ar 0.00934, CO2 0.00038

Natural gas (H/GUS): CH4 0.973, C2H6 0.013, C3H8 0.005, C4H10 0.001, CO2 0.0, N2 0.008

Natural gas (H/North sea): CH4 0.9, C2H6 0.05, C3H8 0.007, C4H10 0.002, CO2 0.01, N2 0.031

Natural gas (L): CH4 0.818, C2H6 0.028, C3H8 0.004, C4H10 0.002, CO2 0.008, N2 0.14

These mixtures can be used for quicker access. But keep in mind that especially for natural gases the compositions of the mixture are only a rough approximation and could deviate for your special mixture of natural gas. So if you know the composition of the mixture it is recommended to add all elements to the mixture instead of the predefined composition.

The fields 'Reference conditions for input' and 'Reference conditions for output'

Data in referenced volume flows (Nm3/h, SCFD, etc) are massflows in disguise. By reference to these conditions - defined by pressure, temperature and relative humidity - a unambiguous density can be calculated for the gas. Then mass flow and volume flow can be converted in each other. However, the determination of density in dependence of pressure and temperature is only trivial for ideal gas behaviour, for real gases it is difficult if not impossible. For converting in every case ideal gas behaviour will be assumed despite the gas doesn't behave ideal. Thus the referenced volume flow becomes a virtual value which doesn't have to match volume flows which have been measured under these conditions. In every case the mass flows behind the volume flows are meant. Data in volume flows are sometimes clearer. If the real conditions roughly met the referenced conditions, the volume flow gives good impression of the amount. For example it is easier to imagine 5 m3 of gas which will be conducted per hour through a tube than e.g. 5 kg.

However, the units Nm3/h, SCFD, etc. are not linked to reference conditions. They give only information about the distribution. Indeed the unit Nm3/h (norm cubic meter per hour) is rather used in Europe while data in SCFD (standard cubic feet per day) will often be found in Britain and North America. Because of this volume flows ALWAYS have to be coupled with reference conditions. Reference conditions can be specified by pressure, temperature and relative humidity or or by reference to a standard, which defines these conditions. The following standards can be selected:

DIN 1343: 1 atm, 0 deg C, humidity = 0
DIN 1945: 1 bara, 20 deg C, humidity = 0
ISO 2314: 14.696 psi, 59 deg F, humidity = 0.6
IUPAC: 1 bara, 0 deg C, humidity = 0
NIST: 1 atm, 0 deg C, humidity = 0
SPE: 14.696 psi, 60 deg F, humidity = 0

Please set the reference conditions for the in- and output units by selecting the standard. Specifications for input- and output reference conditions are only relevant and should be checked if volume flows are used. For converting 'kg/s' in 'kg/h' it doesn't matter what reference conditions have been set.

For a more detailed description of the standards have a look at wikipedia.

Edit the reference conditions

If you want to define the reference conditions by yourself please set the radio buttons to 'edit'. Now it is possible to edit pressure, temperature and humidity directly. To use pressure, temperature and humidity according a standard just reset the radio buttons to 'stnd'.

The fields 'Input' and 'Output'

For converting the massflow has to be typed into the input field. Please type a value and choose an unit in the field 'Input'. Then select the unit in the field 'Output'. By pressing the button 'Calculate' the calculation will be started and the mass flow will be displayed in the output unit. The follwing units can be selected:

massflows: kg/s (kilogram per second), kg/h (kilogram per hour), lb/s (pound per second), lh/h (pound per hour), t/h (metric ton per hour)

volumeflows: SCFM (standard cubic feet per minute), SCFD (standard cubic feet per day) MMSCFD (Million standard cubic feet per day, guess MM is latin and means 1000 x 1000 = 1 million), Sm3/h (standard cubic meter per hour), Nm3/h (norm cubic meter per hour), m3/s (cubic meter per second), m3/h (cubic meter per hour)

molar flows: kmol/h (kilomol per hour), mol/s (mol/second)

dry: For all flows dry means hunidity = 0.0


The following data can be used to verify your calculation:

Air 1.0: 1000 SCFM (14.696 psi, 70 deg F, 0%) -> 1577.5 Nm3/h (1.013 bara, 0 deg C, 0%)

Air 1.0: 1000 SCFM (14.696 psi, 70 deg F, 0%) -> 4493.2 lb/h

Methane 1.0: 1000 SCFM (14.696 psi, 70 deg F, 0%) -> 1128.8 kg/h