I can put in frequency in one box and reactance in another and it will spit out the value of the capacitor

Example 60Hz in one box and 500000 in the reactance and it will tell me 5. some odd nf.

I am looking for the formula that it is using to come up with the cap value from freq and reactance.

I thought I knew this till about half hour ago when I went to figure it out and now I just draw a blank and can't find the answer.

Thanks kindly