Buffer length in feet for feature class in WGS 84

Hi I would like to buffer a polyline feature class in Coordinate System of WGS 84 using 300 feet.

I am getting the error ExecuteError: ERROR 000599: Falls outside of output geometry domains.

I tried to calculate 300ft as decimal degress using a formula found online but the measurement does not come out correctly when measuring in ArcMap. Calculated to 0.00082296 dd, but the measure distance in ArcMap was about 265ft. I did not receive an error however.

The polylines cover most of the 48 states. Would I need to reproject this to a new feature class and then do the calculation? Thank you.

Andrew