Links to dew point calculators.

Temperature, Humidity, Dew Point.   Enter two and it calculates the third.

http://einstein.atmos.colostate.edu/~mcnoldy/Humidity.html

Notes on this calchttps://www.imagepermanenceinstitute.org/environmental/dew-point-calculator
http://www.dpcalc.org/

http://www.decatur.de/javascript/dew/index.html

EG  If the air temp is 66 F and the rel. humidity 32% the dew point is about 35 F according to the first calc. So moisture from the air will condense on a surface that is at 35 F.... cold wall, window, roof, whatever.