Drainage Invert Elevation, Drop, and Cover

Invert-out, total fall, and cover over a gravity run from its slope and length.

Run the calculator

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

Details, formula, and sources

Total 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.

IPC 2021 (International Plumbing Code). Section 704 (drainage piping slope minimums).

Free read-only access at codes.iccsafe.org.

Estimate. AHJ and licensed professional govern.

Field names used by the API: invert_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