Calculate pipe grade, fall per 100 feet, and minimum grade compliance from manhole invert elevations. Essential for CIPP lining pre-inspection, sewer main surveys, and pipe laser setup. Enter upstream and downstream invert elevations and pipe length — this calculator instantly shows you the grade, total fall, and whether the run meets minimum IPC requirements for your pipe diameter.
CIPP (Cured-In-Place Pipe) lining installs a resin-impregnated felt liner that cures against the host pipe walls, creating a smooth structural pipe within a pipe. Unlike traditional pipe replacement, CIPP is trenchless — but it cannot correct grade deficiencies. If the host pipe has sags, reverse grades, or sections below minimum slope, lining over them locks those defects in place permanently.
Before any CIPP project, the pre-CCTV inspection crew verifies grade manhole-to-manhole using a pipe laser. The laser is set at the upstream manhole at the invert elevation and grade, then shot down to the downstream MH. Grade readings are taken at intermediate stations — typically every 25 or 50 feet — and compared to the design grade. Deviations greater than ±0.05 feet are flagged for review by the project engineer.
| Diameter | Min Grade (%) | Fall per 100ft | Reference |
|---|---|---|---|
| 4" | 1.04% | 1.04 ft | IPC Table 704.1 |
| 6" | 0.50% | 0.50 ft | Civil min — gravity sewer |
| 8" | 0.40% | 0.40 ft | Civil min — gravity sewer |
| 10" | 0.28% | 0.28 ft | Design-specific |
| 12" | 0.22% | 0.22 ft | Design-specific |
| 15"+ | Engineer specified | — | Per hydraulic design |
Subtract the downstream invert elevation from the upstream invert elevation to get total fall, then divide by pipe length and multiply by 100 to get grade percentage. Example: upstream invert 7041.220, downstream invert 7040.820, length 400ft. Fall = 7041.220 − 7040.820 = 0.400ft. Grade = (0.400 ÷ 400) × 100 = 0.100%.
The invert elevation is the elevation of the inside bottom of the pipe at a given point — typically measured at a manhole. It differs from the pipe centerline or crown elevation. For gravity flow calculations, inverts are the relevant measurement because water flows along the pipe bottom.
CIPP (Cured-In-Place Pipe) lining does not change the pipe grade — it follows the existing profile. Before lining, the host pipe must be verified to have adequate grade. For 8-inch sewer pipe the typical minimum is 0.40%. If grade is insufficient, lining over a sag or reverse-grade section will not fix drainage and may void the project warranty.
Fall per 100 feet is a common field expression of pipe grade: the number of feet the pipe drops over 100 horizontal feet. A 0.5% grade drops 0.5 feet (6 inches) per 100 feet. It's equivalent to grade percentage expressed as a decimal. Pipe lasers and some digital levels use this unit directly.
Set a pipe laser at the upstream manhole at the measured invert elevation, aligned to the design grade. Shoot the beam down to the downstream manhole. Use a grade rod or laser target at intermediate stations to verify the actual invert matches the laser beam. Record deviations and flag any station more than 0.05ft out of spec.
Calculate pipe grade from manhole invert elevations for CIPP lining surveys, sewer main work, and pipe laser setup. Enter upstream and downstream inverts and pipe length.
Need a pipe laser for CIPP grade verification? Spectra DG813, Topcon TP-L4, and Leica Piper 200.
Shop Express Tools →Subtract the downstream invert elevation from the upstream invert elevation to get total fall, then divide by pipe length and multiply by 100 to get grade percentage. Example: upstream invert 7041.220, downstream invert 7040.820, length 400ft. Fall = 7041.220 − 7040.820 = 0.400ft. Grade = (0.400 ÷ 400) × 100 = 0.100%.
The invert elevation is the elevation of the inside bottom of the pipe at a given point — typically measured at a manhole. It differs from the pipe centerline or crown elevation. For gravity flow calculations, inverts are the relevant measurement because water flows along the pipe bottom.
CIPP (Cured-In-Place Pipe) lining does not change the pipe grade — it follows the existing profile. Before lining, the host pipe must be verified to have adequate grade. For 8-inch sewer pipe the typical minimum is 0.40%. If grade is insufficient, lining over a sag or reverse-grade section will not fix drainage and may void the project warranty.
Fall per 100 feet is a common field expression of pipe grade: the number of feet the pipe drops over 100 horizontal feet. A 0.5% grade drops 0.5 feet (6 inches) per 100 feet. It's equivalent to grade percentage expressed as a decimal. Pipe lasers and some digital levels use this unit directly.
Set a pipe laser at the upstream manhole at the measured invert elevation, aligned to the design grade. Shoot the beam down to the downstream manhole. Use a grade rod or laser target at intermediate stations to verify the actual invert matches the laser beam. Record deviations and flag any station more than 0.05ft out of spec.