Plumbing Roof Drain Flow Rate Calculator
Actual independently governing rain intensity×roof area×runoff fraction roofinflowm³/s, no drain capacity/code-rain period selected. Actual independently matched units, regime, material/equipment and governing references; not a hydraulic code, safe pressure, water pot ability or operational approval.
Description
Roof runoff relates rain intensity, contributing area and a runoff fraction.
Roof runoff relates rain intensity, contributing area and a runoff fraction.1
The estimated inflow is distinct from drain or leader capacity. The calculation and input requirements are explained below.
When to use Plumbing Roof Drain Flow Rate Calculator
Enter nonnegative rain intensity m/s and contributing roof area m², plus independently calibrated runoff fraction 0–1.
How to use Plumbing Roof Drain Flow Rate Calculator and how it works
- Prepare the measurements or independently established model inputs described below, with matching units and observation scope.
- Enter the required fields and run Plumbing Roof Drain Flow Rate Calculator.
- Read the result fields using the formula, output units, signs and ordering explained below.
- Correct any rejected inputs and rerun; interpret the result within the stated model and its assumptions.
| Input field | Meaning | Value type | Requirement |
|---|---|---|---|
| actualRainIntensityMetersPerSecond | Actual Rain Intensity Meters Per Second. Use the units and matching context stated in the calculation below. | number | Required; nonnegative; finite; other constraints below |
| actualContributingRoofAreaSquareMeters | Actual Contributing Roof Area Square Meters. Use the units and matching context stated in the calculation below. | number | Required; nonnegative; finite; other constraints below |
| callerCalibratedRoofRunoffFraction | Caller Calibrated Roof Runoff Fraction. Use the units and matching context stated in the calculation below. | number | Required; fraction from 0 to 1; finite; other constraints below |
Enter nonnegative rain intensity m/s and contributing roof area m², plus independently calibrated runoff fraction 0–1. Multiply to return roof inflow m³/s. Drain conveyance capacity and design storm are not selected.
roofInflowM3ps=rainIntensityMps*roofAreaM2*runoffFraction Apply the input ordering, units and branch conditions stated above.
| Output field | Meaning | Value type |
|---|---|---|
| result | Object containing the calculated or selected fields below. | object |
| result.value | Numeric result under the formula and output units explained above. | number |
{
"input": {
"actualRainIntensityMetersPerSecond": 1,
"actualContributingRoofAreaSquareMeters": 10,
"callerCalibratedRoofRunoffFraction": 0.5
},
"output": {
"result": {
"value": 5
}
}
}Limitations and assumptions
The calculation uses the supplied observations and model inputs. It does not collect measurements, select a reference population or coefficient, or establish that the model applies to the actual case. The stated branch conditions and output units remain part of the result.
All fields require explicit values. Unexpected fields, wrong types, nonfinite numbers and sparse arrays are rejected. Alignment, bounds and supported-token rules are explained above; extremely large inputs or nonfinite results can also fail. Input errors differ from successful false comparisons, unavailable-domain flags and empty match lists.
Alternative or Complementary methods
Use Plumbing Scuppers Size Calculator for a complementary operation: Scuppers convey roof runoff through a defined opening.
Use Plumbing Roof Drain Leader Size Calculator for a complementary operation: Roof leaders convey drainage from roof outlets.
References
-
Plumbing Roof Drain Flow Rate Calculator — tool.io
Similar or alternative tools
- Plumbing Scuppers Size Calculator
Scuppers convey roof runoff through a defined opening.
- Plumbing Roof Drain Leader Size Calculator
Roof leaders convey drainage from roof outlets.