# Units of time in solver **URL:** \ **Category:** Cases\ **Created:** [7 March 2023 02:42 UTC](https://pyfr.discourse.group/t/units-of-time-in-solver/766 "2023-03-07T02:42:43Z")\ **Posts on this page:** 4\ **Page:** 1
**Author:** ![fei](https://avatars.discourse-cdn.com/v4/letter/f/59ef9b/32.png) [@fei](https://pyfr.discourse.group/u/fei)\ **Post date:** [7 March 2023 02:42 UTC](https://pyfr.discourse.group/t/units-of-time-in-solver/766/1 "2023-03-07T02:42:43Z")
Hello, everyone. Is the unit of time t in the source term is seconds (s)? For example, I want the source term to work within 1 subtle (us), then I make the working interval is 0≤t\<1e-6. Is this right? With best regards ---
**Author:** ![WillT](https://avatars.discourse-cdn.com/v4/letter/w/bc79bd/32.png) [@WillT](https://pyfr.discourse.group/u/WillT)\ **Post date:** [7 March 2023 08:44 UTC](https://pyfr.discourse.group/t/units-of-time-in-solver/766/2 "2023-03-07T08:44:56Z")
In PyFR we don’t assume or impose any units, you might like to have a look at these two topics where it is discussed: > [@Units for mass, length and time](https://pyfr.discourse.group/t/units-for-mass-length-and-time/100): > > Hi Developers, A current feature of PyFR is that it can operate in any consistent system of units. Would it be possible to add the ability to use a specific system of units; SI, for example? At present, any scale factors used to non-dimensionalize a given PyFR case must be recorded separately. The .ini file has no means of recording and communicating the factors used. To give an example of the kind of question that can arise, one might be interested to know the viscosity of the gas used in a p… > [@State equations and viscosity](https://pyfr.discourse.group/t/state-equations-and-viscosity/377): > > Hello all, several questions about the navier stokes solver. couldnt find answers in the user’s guide What state equation is employed in solution of navier-stokes? Is it the ideal gas equation? What if I want to solve a problem with a different state equation? What units (if any) should the viscosity in “Navier-stokes” solver given in? Is it unitless? If so- what is it scaled by? What confuses me is that in the Couette flow example we were given a viscocity of ~0.4, which is huge in SI units. I… ---
**Author:** ![fei](https://avatars.discourse-cdn.com/v4/letter/f/59ef9b/32.png) [@fei](https://pyfr.discourse.group/u/fei)\ **Post date:** [7 March 2023 09:36 UTC](https://pyfr.discourse.group/t/units-of-time-in-solver/766/3 "2023-03-07T09:36:44Z")
Ok, that means when I use the dimentional values in the .ini file, then times t in the source term is SI, and it’s unit is seconds? ---
**Author:** ![WillT](https://avatars.discourse-cdn.com/v4/letter/w/bc79bd/32.png) [@WillT](https://pyfr.discourse.group/u/WillT)\ **Post date:** [7 March 2023 09:49 UTC](https://pyfr.discourse.group/t/units-of-time-in-solver/766/4 "2023-03-07T09:49:56Z")
If you intend for your mesh to be interpreted as 1 is 1m and your velocity is to be interpreted as 1 being 1ms^{-1}, then yes your time will be in seconds.