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Pipe Slope Calculator

invert 1 [m a.s.l.]

invert 2 [m a.s.l.]

L [m]

i [%]

Pipe Elevation Calculator

elev. 1 [m a.s.l.]

elev. 2 [m a.s.l.]

Length [m]

Distance from manhole 1 [m]

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Sewer slope calculator — calculating elevations and slopes of sewer lines

Professional calculator for determining the slope of sewer pipes based on terrain elevations and section length. The tool operates in two modes: calculating slope from given elevations (H1, H2, L) or determining the end elevation from a given slope and length. An additional module calculates the elevation at any intermediate point along the sewer route. Designed for sewer network designers, surveyors and construction managers.

How to use the calculator in 3 steps

Enter the starting elevation H1 [m above sea level] and ending elevation H2 [m above sea level] of the sewer, along with the horizontal section length L [m]. The calculator will automatically compute the slope in percent [%] and per mille [‰].

Alternatively: enter the starting elevation H1, the required slope [%] and length L — the calculator will determine the ending elevation H2. Useful when designing a sewer with a predetermined minimum slope.

Use the intermediate point module: enter the distance from the start of the sewer, and the calculator will compute the pipe invert elevation at that point. You can use the slider for smooth distance adjustment.

Sewer slope — formula and principles

The sewer slope is calculated using the formula: S = (H1 − H2) / L × 100%, where H1 is the starting elevation [m above sea level], H2 is the ending elevation [m above sea level], and L is the horizontal section length [m]. The result is expressed in percent [%] or per mille [‰] (1% = 10‰).

Minimum slopes for gravity sewers follow the 1/DN rule — the minimum slope is the inverse of the pipe diameter. For DN 200 it is 0.5% (5‰), for DN 300 — 0.33% (3.3‰), for DN 400 — 0.25% (2.5‰). Slopes below these values risk sediment accumulation and pipe blockage.

Maximum slopes are limited due to pipe erosion and the risk of sewage phase separation. For PVC/PP pipes, the maximum slope is 15% (DN ≤ 200) to 10% (DN > 200). For vitrified clay pipes — 10% and 8% respectively.

Proper slope should ensure self-cleaning velocity: min. 0.7 m/s for sanitary sewers and min. 0.5 m/s for storm sewers. At the same time, velocity should not exceed 5 m/s (sanitary) or 7 m/s (storm) — excessive velocity causes pipe material erosion.

Design tips

Practical advice when designing sewer slopes:

Always verify geodetic elevations in the field before starting the design — differences between the map and actual conditions may force slope changes.
For deeply laid sewers (over 3 m), consider using cascade manholes instead of steep slopes, which reduces erosion and facilitates maintenance.
When designing storm sewers, remember that minimum slopes are lower than for sanitary — e.g., DN 300 requires min. 0.2% (2‰) instead of 0.33%.
The intermediate point calculator is useful when coordinating elevations at crossings with other underground utilities — check for conflicts.