Drainage Invert Elevation, Drop, and Cover
Invert-out, total fall, and cover over a gravity run from its slope and length.
Example
You enter
- Invert-in elevation (ft) 100
- Slope 0.25
- Slope units in_per_ft
- Run length (ft) 80
- Pipe OD (in) 4.5
- Downstream surface elevation (ft, optional) 102
- Minimum cover (ft, optional) 2
You get
- Total fall 1.67 ft
- Invert-out 98.33 ft
- Top of pipe 98.71 ft
- Cover 3.29167
- Cover flag No
Checked against published worked examples from: Washington Suburban Sanitary Commission (WSSC Water).
Details, formula, and sources
Formula or tableTotal fall = slope x run; invert-out = invert-in - fall; top of pipe = invert-out + OD; cover = surface - top of pipe. Slope entered as in/ft or percent, normalized to ft/ft.
Source and editionIPC 2027 (International Plumbing Code). Section 704 (drainage piping slope minimums).
Free accessFree read-only access at codes.iccsafe.org.
What governsEstimate. AHJ and licensed professional govern.
API field namesinvert_in_ft, slope, slope_units, run_ft, pipe_od_in, surface_out_ft, min_cover_ft, total_fall_ft, invert_out_ft, top_of_pipe_ft, cover_out_ft, cover_flag
- Cover datum cover measured from finished grade to the top of the pipe (invert-out + OD / 12)standard trench-section geometry
- Sign convention a negative cover (pipe crown above grade) is flagged, not rejectedspec-v163 output contract