How is downstream invert elevation calculated?

For a pipe flowing to a lower downstream point, downstream invert equals upstream invert minus the calculated fall over the horizontal run.

What is an invert elevation?

Invert elevation is the elevation of the inside bottom of a pipe or conduit at a defined location.

Can the calculator work uphill?

The standard mode assumes a positive drainage slope and calculates a lower downstream invert. Reverse direction can be handled by changing which point is treated as upstream.

Drain invert levels

Drain Pipe Invert Elevation Calculator — Find the Downstream Level

Start with a known upstream invert elevation and calculate the downstream invert after applying a drainage slope over a defined horizontal run.

Invert inputs

Upstream invert elevation

Horizontal run

Slope format

Slope value

Run / elevation unit

This assumes the downstream point is lower than the upstream point. Elevation zero datum is whatever datum your project uses.

Enter upstream invert, run and slope.

Invert elevation result

Downstream invert

—

—Upstream invert

—Calculated fall

—Slope

—Run

—

Downstream invert formula

Fall = run × decimal slope
Downstream invert = upstream invert − fall

Why the horizontal run is important

The calculation assumes the run is measured horizontally. A sloping pipe's 3D physical length is slightly different, but drainage profile calculations commonly start from horizontal stationing and vertical fall.

Datum matters

All elevations must use the same project datum. The calculator performs arithmetic only; it does not transform between survey datums.

Worked example

Upstream invert 102.400 m, 20 m run and 1.5% slope:

Fall = 20 × 0.015 = 0.300 m
Downstream invert = 102.400 − 0.300 = 102.100 m

Frequently Asked Questions

What is the invert?

It is the elevation of the inside bottom of the pipe at the stated location.

Can I use a ratio such as 1:100?

Yes.

Does this calculate pipe diameter?

No.

Can I use negative elevations?

Yes. An invert may be above or below an arbitrary datum, as long as the entered values use a consistent reference.