From the first structure to the next I need to rise 2.3 ft. It's a 48 ft run. Does anyone know the formula to find the percent so I can set the piper laser?
100(rise/run) for yours its (100)(2.3/48) which gives you 4.79% and to check you can do 48X 0.0479 and it gives you 2.2992 which is 2.3 feet or close enough.
What Eric said.
Don't know if this applies to you, but thought I would mention it: Around here it's common for some engineers to measure a run of pipe from center of structure to center of structure. So if the plans say 48' of pipe @ 2.0% slope and the structures are both 48" diameter catch basins, the run may really be only 44' long and you will be low when you get to the second structure if your laser is set at 2.0%. In this case you would have to be set at 2.18% to hit your second structure correctly.