# Calculating thrust pressure from ion thruster for rocket thrust equation

So recently i have been very interested in the possibilities of using ion thrusters as power interstellar propulsion units, however when it comes to calculating ISP it have absolutely zero idea how you calculate the mass flow rate of the ionised particles or the pressure in the thrust beam. I am guessing the mass flow rate depends on the method of ionisation but it is there a way to work this out? Thank you very much!

Then the three things you're talking about are related simply: $$T=g_n I_{sp}{dm\over dt}$$, where $$g_n$$ is the standard gravitational acceleration at the surface of the Earth, which by convention is exactly $$9.80665\,\mathrm{m/s^2}$$.
So for example if you are flowing 60 milligrams of propellant per minute into your ion engine, that's a mass flow rate $${dm\over dt}$$ of $$1\times 10^{-6}$$ kg/sec. If your mass-specific impulse $$I_{sp}$$ is 5,000 seconds, then your Thrust $$T$$ = $$(9.81) \times (5 \times 10^{3}) \times (1\times 10^{-6}) \approx 0.049$$ Newtons of force.