calculate the cutoff frequency of a low pass filter
Yes
You must convert the units from cycles per second to radians per second using  ω = 2πf

or
 f=1/(2πRC)

as you have done.

But since component tolerances are rarely &lt; 1% , prudent answers only use 3 sigfigs.  

so 25.3kHz is close enough, otherwise you look like a rookie.