You need to look at your chosen board stack up materials and dimensions and then use one of the calculators below: Rogers supply the very nice MWI-2020 tool (and their ring resonator tool is great for helping characterise the substrate material) for free: [https://rogerscorp.com/Tools](https://rogerscorp.com/Tools) and for other work, a free multi-layer dielectric field solver tool such as mdtlc: [http://mdtlc.sourceforge.net/](http://mdtlc.sourceforge.net/) and this free tool is priceless: [http://www.hp.woodshot.com/](http://www.hp.woodshot.com/) (IIRC, it runs OK on linux using WINE.)

I used the JPLPCB tool available on their web page. The track width 5.78mi is clear, I don't only understand what distance from track I should set to GND, 5.78mi or another distance? "G" distance in the picture below. 

@Caster, JLCPCB's tool: [https://cart.jlcpcb.com/impedanceCalculation?_ga=2.263666116.939889772.1603636980-139248169.1592496815](https://cart.jlcpcb.com/impedanceCalculation?_ga=2.263666116.939889772.1603636980-139248169.1592496815) does not include coplanar waveguide. That's why I pointed you to the MWI and mldtlc tools. There are other online tools available but I have used these two and can vouch for their accuracy.

@andyfierman Thank you. I have decided to use just the microstrip because of the space constraints. I tried out elliptic integrals in Excel to calculate the Coplanar Waveguide with Lower Ground Plane ;-).

Excel would not be my tool of choice something like that but how did your sims compare with mldtc for a given PCB stack up?

JPLPCB recommends for JLC2313 material (0.035 0.1 mm) 50 Ohm microstrip trace width 5.78mils (0.147mm) for four layers. I calculated 6.92mils (0.176mm) to achieve 50.058 Ohm. The Excel has a great advantage to use Sensitivity analysis (Data)  e.g to let you calculate any parametr in an equation based on other values. You can for example input required microstrip resistance (in Ohm's) value and let Excel automatically calculate the width of the strip. On line or program calculators can't do it usually that just calculates you Ohm value based on all input parameters. You need repeatedly change input parameters to achieve required resistance.

The calculated values are only as good as the data you put in and the formula you are using. Have you included the additional effect of the dielectric constant of the solder mask over the traces? I would recommend that you sanity check your calculations against mldtc.