FREE FIELD CALCULATOR
Pipe invert station table
Start with one known invert and the plan grade, then build the inverts you should see at each station.
What you’ll need
- The known starting pipe invert, in decimal feet
- The grade shown on the plans, as a percent
- The pipe length and the station interval you want to check
- The direction you are working and any structure drop at the far end
Enter the run above.
You will get the end invert, total fall and a station table with distance, invert and cumulative fall.
Try it with these numbers
- Enter start invert 100.00 ft, grade 0.50% and length 200 ft.
- Use a 50 ft station interval, choose Downstream and leave structure drop blank.
- Choose Calculate invert table. The ending invert should be 99.00 ft.
- Check the rows: 0+50 is 99.75, 1+00 is 99.50, 1+50 is 99.25 and 2+00 is 99.00.
Reading your result
End invert is the calculated pipe flow-line elevation at the far end. Grade fall (or grade rise upstream) is caused by the constant pipe slope. Structure drop is shown separately and changes only the last station.
Use the station table to check layout or field readings. A row is a calculated target from the inputs you supplied; it is not a measured shot.
How the math works
- Grade fall = length × (grade percent ÷ 100). A 0.50% grade falls 0.50 ft in 100 ft.
- Downstream subtracts that fall from the start invert. Upstream adds it.
- Structure drop, if entered, applies at the last station only: downstream it is subtracted, upstream it is added. Intermediate stations follow the grade.
- Total fall (downstream) or total rise (upstream) = grade change + structure drop.
- Stations start at 0+00 and step by the interval. The exact ending station is always included.
Start invert 100.00 ft, grade 0.50%, length 200 ft, interval 50 ft, downstream, no structure drop.
Grade fall = 200 × 0.50 ÷ 100 = 1.00 ft. End invert = 100.00 − 1.00 = 99.00 ft.
Stations: 0+00 at 100.00, 0+50 at 99.75, 1+00 at 99.50, 1+50 at 99.25, 2+00 at 99.00. Cumulative fall at the end is 1.00 ft.
Where this goes wrong on site
Percent per hundred, not per foot. 0.50% is half a foot in 100 ft, not half a foot in one foot. Convert a rise and run with the slope and grade calculator first if you measured two inverts instead of reading a percent off the plans.
Pick a direction and stay with it. Downstream is the usual flow direction: invert falls as station increases. Use upstream when you are working from the low end back toward the high end.
Drop is at the ending structure. Incoming versus outgoing invert at the starting manhole belongs in the start invert you type. This field is the drop at the far structure: it lowers the ending invert working downstream and raises it working upstream.
Constant grade on one run. A pipe that changes grade, or a line with several structures, should be split into separate calculations.
Keep the table with the job
This free table is for the run in front of you. The Driftless Field workspace keeps pipe invert sheets with stations, grades, target elevations and observation notes against a named job, and prints them as a record.
Read the free-calculator guide for offline use, exports and result sheets.
Early access is free for now when you want saved invert sheets, field-book shots and a job report. The calculation above stays on this device unless you share it.
Useful on your job?
Share this free calculator with someone who could use it, or tell Jesse what needs improving.
Shares the tool link only, without your measurements. https://driftlesssolutions.us/tools/pipe-invert/