Partially Full Pipe Flow Calculator
Calculate circular segment flow area, hydraulic radius and uniform Manning flow below a pipe crown.
YOUR CALCULATION
Result
—
Calculation steps
Work through one step at a time or reveal the complete calculation. The steps use your current inputs.
How to calculate
Find the wetted circular segment and apply Manning’s SI uniform open-channel relation.
θ=2acos(1−2y/D); A=D²(θ−sinθ)/8; P=Dθ/2; Q=A(A/P)^(2/3)√S/n
Worked example
At half-full depth, area is half a circle and hydraulic radius is D/4; modeled velocity equals the same pipe’s full-area Manning velocity at the same slope and n.
Assumptions and input details
Depth must lie strictly between zero and diameter. Uniform free-surface flow only, no surcharging, backwater, entrance/outlet losses or inferred roughness. Near-empty sections may lose relative precision.
Unit definitions
Unit selection is independent of language. Each selector contains only units for its physical quantity. Calculations use defined base units internally.
Choose from 23 length definitions, including explicitly labelled regional measures. Area conversions square the length factor; geometric volumes cube it.
Regional measures are not interchangeable merely because their names look similar. This is a documented selection, not a claim to include every historical unit.
NIST measurement tables · Japanese traditional units · Mainland China and Hong Kong unit distinctions
Using this calculator
Can I enter my own problem?
Yes. Replace the example values with your own inputs. The result, calculation steps, tables and applicable diagrams update from those inputs. Blank or invalid values clear the result; example values are never silently substituted for missing inputs.
Are the results exact?
Results use floating-point arithmetic and displayed rounding. Read the formula, assumptions and any stated data precision before interpreting the result.
Is my input uploaded?
The calculation runs in your browser. No account, file upload or external AI service is required. Inputs are not saved between page reloads.
Estimate uniform flow in a rectangular, triangular or symmetric trapezoidal channel using entered SI Manning roughness.
Estimate straight circular-pipe and entered minor losses with an explicit Darcy friction factor convention.
Find a circular segment’s area, chord, arc and boundary length from radius and segment height, including major segments.
Reserved advertising space.