Free civil tool · Metric · No signup
Pipe Grade & Invert Calculator
Find fall and grade from upstream and downstream inverts, or calculate the downstream invert needed for a chosen gradient.
Example inputs are editable. Use your project values. Enter 0 where no optional allowance is intended; blank fields pause the calculation.
Your inputs
Your results
- Fall
- 0.595 m
- Fall in millimetres
- 595 mm
- Grade
- 1.4 %
- Fall per metre
- 14 mm/m
- Ratio
- 1 : 71.43
Calculation breakdown
Fall = 12.84 − 12.245 = 0.595 m
Grade = (12.84 − 12.245) ÷ 42.5 × 100 = 1.4 %
Displayed values are rounded. The calculation uses unrounded inputs.
These free results do not automatically save or sync to a Fieldlink job.
How it works
- Fall = upstream invert − downstream invert
- Grade % = fall ÷ horizontal length × 100
- Ratio magnitude 1:X, where X = length ÷ |fall|
- Required fall = length ÷ X
- Downstream invert = upstream invert − required fall
- Run at chosen falling gradient = positive fall × X
Worked example
42.5 m horizontal run: upstream IL 12.840 m, downstream IL 12.245 m. Fall = 0.595 m = 595 mm. Grade = 1.4%; ratio = 1:71.43.
Assumptions and practical notes
Positive fall means the downstream invert is lower. A negative fall is an adverse rise in the stated direction; zero is level. Inverts may be negative relative to a datum. Displayed inverts are rounded to 0.001 m; this is display precision, not survey accuracy.
Use project drawings and specified gradients. This arithmetic does not check hydraulic capacity or certify a drainage design.
Working on the full job?
Use the quantities when reviewing the drainage scope and estimate.