Calculate pipe invert elevations along any gravity sewer or storm drain run. Enter starting invert, pipe grade %, and run length to get ending invert elevation, total drop, and a station-by-station table.
Set pipe to exact invert elevation with a Spectra DG711, Leica Piper 200, or Topcon TP-L6GV pipe laser.
Shop Express Tools →Invert elevationis the elevation of the inside bottom of a pipe at a given point. It is the single most important elevation reference for gravity sewer and storm drain design and construction. The term "invert" comes from inverted arch — the bottom of the pipe forms an arch inverted from the top.
Every manhole on a plan-and-profile drawing will show both an invert in (elevation of the bottom of the incoming pipe) and an invert out (elevation of the bottom of the outgoing pipe). The invert out is always lower than the invert in by the manhole drop — the amount needed to maintain hydraulic grade through the structure.
Underground utility crews use invert elevation calculations constantly — before installation to set up the pipe laser, during installation to verify hub elevations match the design invert table, and after installation during as-built survey. A foreman setting up a Topcon TP-L6GV pipe laser needs to know the exact invert at both ends of the run, then calculates the grade setting from those two inverts and the run length.
Inspectors use invert elevation verification to confirm installed pipe matches design intent. After a manhole is poured, the inspector drops a tape to measure depth-to-invert and compares against the as-built invert elevation. Discrepancies of more than 0.1 ft typically require documentation or correction before the project can proceed. This calculator helps inspectors quickly verify measurements against plan values without separate spreadsheets.
Invert elevation is the elevation of the inside bottom of a pipe at a specific location — the lowest point of the pipe interior where flow travels. Unlike the pipe centerline or outside diameter, the invert is the hydraulic reference point for gravity flow design. Invert elevations at each manhole tell crews exactly how deep to place pipe and how to set the pipe laser for each run.
Invert elevation at any downstream point = starting invert − (grade% ÷ 100 × distance). Example: starting invert 100.00 ft, 0.5% grade, 200 ft downstream → 100.00 − (0.005 × 200) = 99.00 ft. For upstream calculations, add instead of subtract. This calculator handles both directions and generates a station table automatically.
Invert elevation is the inside bottom of the pipe. Rim elevation is the top of the manhole frame at the ground surface. Rim elevation minus invert elevation equals total depth to pipe invert, which determines how deep a manhole needs to be. If rim elevation is 102.50 ft and invert is 98.25 ft, the manhole depth is 4.25 ft.
On plan-and-profile drawings, invert elevations appear as "Inv. = xxx.xx" at each structure. The profile view shows the pipe drawn at design grade with inverts annotated at manholes and catch basins. Field crews use these to confirm invert elevations before setting the pipe laser and to verify installations match design during inspection.
Incorrect invert elevations create sags (reverse grades) that trap solids and cause blockages. Every manhole-to-manhole run must be installed within tolerance — typically ±0.1 ft, sometimes ±0.05 ft — to maintain the design hydraulic grade line. A single sag in a 1,000-foot gravity sewer can cause repeated service calls and costly spot repairs.