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Pipe Fall Calculator

Calculate exact millimeter drops and invert levels for laser setups instantly.

250mm

Total Pipe Drop (Fall)

40

1 in 40 Ratio

Start (High)End (Low)

Pipe Run & Fall

10.000m

Invert Levels (Optional)

Enter your starting invert level to automatically calculate the exact depth your pipe needs to hit at the end of the run.

100.000m

End Invert Level

Calculated target depth

99.750m
## Calculating Drainage Gradients Setting up drainage runs correctly is critical. If a pipe is laid too flat, water and solids will pool and block the system. If it is laid too steep, the water will run away too quickly, leaving the solids behind to cause a blockage. The gradient of a pipe is expressed as a ratio, typically **1 in X** (e.g., 1:40). This means for every 40 units of horizontal run, the pipe drops by 1 vertical unit. ### Standard Building Regulations (UK) * **1:40 Gradient (2.5%):** The standard fall for 110mm surface water and foul drainage pipes carrying standard household effluent. * **1:80 Gradient (1.25%):** Often used for larger 160mm pipes or runs with a continuous flow (where at least one WC is connected). * **1:100 Gradient (1%):** Reserved for very large commercial pipes or clean surface water drains where solid clearance is less of an issue. ### What is an Invert Level? The "Invert Level" (IL) is the lowest inside point of the pipe. It is the surface that the water actually flows on. When groundworkers use pipe lasers or boning rods, they are calculating the drop from the Start Invert Level to the Target End Invert Level. Our calculator allows you to input an exact starting elevation (e.g., from your datum point) and will automatically generate the exact target elevation you need to hit by the end of your run. --- ## Explore More Site Tools
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