Rational Method Stormwater Peak Runoff (Q = CiA) & GPM Calculator

Compute site peak stormwater runoff Q = C·i·A in CFS and GPM.

Peak Stormwater Discharge (Q)
5.69 CFS
Peak Discharge in Gallons / Min 2,552.73 GPM
1-Hour Storm Runoff Volume 153,163.58 gallons
Impervious Equivalent Acres (C × A) 1.63 acres
Inputs
acres
Total drainage catchment area (A) in acres.
C (0–1)
Surface runoff coefficient C (0.20 lawn, 0.65 residential, 0.90 paved).
in/hr
Design storm rainfall intensity (i) in inches per hour.
Results & Graph
Peak Stormwater Discharge (Q)
5.69 CFS
Peak Discharge in Gallons / Min
2,552.73 GPM
1-Hour Storm Runoff Volume
153,163.58 gallons
Impervious Equivalent Acres (C × A)
1.63 acres

Peak Stormwater Discharge (Q)

Graph 1 • Catchment Area Acres Sensitivity Recalculates the domain equation across 50% to 150% of the primary input while holding other parameters constant.
0 CFS 4.6 CFS 9.2 CFS 50%: 2.84 CFS 2.8 50% 75%: 4.27 CFS 4.3 75% 100%: 5.69 CFS 5.7 100% 125%: 7.11 CFS 7.1 125% 150%: 8.53 CFS 8.5 150%
Graph 2 • Primary & Supporting Metric Comparison Compares the primary output alongside supporting domain benchmarks.
Peak Stormwater Discharge (Q) 5.69 CFS Peak Discharge in Gallons / Min 2,552.73 GPM 1-Hour Storm Runoff Volume 153,163.58 gallons Impervious Equivalent Acres (C × A) 1.63 acres
Graph 3 • Exact Output Table & Units Displays each calculated output in its exact domain unit.
Peak Stormwater Discharge (Q)5.69 CFSPeak Discharge in Gallons / Min2,552.73 GPM1-Hour Storm Runoff Volume153,163.58 gallonsImpervious Equivalent Acres (C × A)1.63 acres
Summary: Across 2.5 acres (C=0.65) under a 3.5 in/hr storm, peak Rational Method runoff is 5.69 ft³/s (2,553 GPM).
Summary: Across 2.5 acres (C=0.65) under a 3.5 in/hr storm, peak Rational Method runoff is 5.69 ft³/s (2,553 GPM).
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Formula & Mathematical Methodology: Stormwater Runoff (Q=CiA) Formula

Qcfs = RunoffCoeffC × Intensityin/hr × Areaacres
FlowGPM = Qcfs × 448.83
Q_cfs = RunoffCoeff_C × Intensity_in/hr × Area_acres; Flow_GPM = Q_cfs × 448.83
  • catchmentAreaAcres: Catchment Area Acres (acres)
  • runoffCoefficientC: Runoff Coefficient C (C (0–1))
  • rainfallIntensityInHr: Rainfall Intensity In Hr (in/hr)

Rounding: Physical package counts round up where appropriate; continuous measurements round to 2 decimal places.

Worked Example: Practical Benchmark: Stormwater Runoff (Q=CiA)

Compute site peak stormwater runoff Q = C·i·A in CFS and GPM.

  1. Enter your project dimensions, machining speeds, or recipe weights.
  2. Compute the governing equation: Q_cfs = RunoffCoeff_C × Intensity_in/hr × Area_acres; Flow_GPM = Q_cfs × 448.83.
  3. Review the primary result, supporting dimensions, and 3 SVG visualizations.
Result: Computes Stormwater Runoff (Q=CiA) via Q_cfs = RunoffCoeff_C × Intensity_in/hr × Area_acres; Flow_GPM = Q_cfs × 448.83.

Frequently Asked Questions

How does the Rational Method Stormwater Peak Runoff (Q = CiA) & GPM Calculator calculate results?

It evaluates Q_cfs = RunoffCoeff_C × Intensity_in/hr × Area_acres; Flow_GPM = Q_cfs × 448.83 directly in your browser and plots three custom SVG visualizations.

Can I compare different material dimensions or batch sizes side by side?

Yes. Click "Compare (0/3)" in the results toolbar to pin up to 3 scenarios side by side.

Can I print a clean shop or kitchen reference sheet?

Yes. Click the Print button in the results toolbar for a distraction-free worksheet.

Construction & Home · Sitework & Paving

Rational Method Stormwater Peak Runoff (Q = CiA) & GPM Calculator: inputs, method, and how to read the result

Compute site peak stormwater runoff Q = C·i·A in CFS and GPM.

Choose inputs for the case you are checking

The defaults are illustrative. Replace them with values for your case and keep the units shown beside each field.

  • Catchment Area Acres: Total drainage catchment area (A) in acres.
  • Runoff Coefficient C: Surface runoff coefficient C (0.20 lawn, 0.65 residential, 0.90 paved).
  • Rainfall Intensity In Hr: Design storm rainfall intensity (i) in inches per hour.

What the calculation includes

With the default values shown, Peak Stormwater Discharge (Q) is 5.69 CFS. The calculation follows Stormwater Runoff (Q=CiA) Formula; the formula and variable definitions above show how the inputs combine.

One-input check: With the other defaults held constant, changing Catchment Area Acres from 2.5 acres to 2.75 acres changes Peak Stormwater Discharge (Q) from 5.69 CFS to 6.26 CFS. This is a comparison inside the calculator's stated model, not a prediction.

Where to use caution

  • Uses standard North American & metric trade dimensions, Machinery’s Handbook formulas, and culinary weight ratios.
  • Verify local municipal building codes, tool manufacturer limits, and food-safety time/temperature tables before execution.

Scope: Trade, Shop & Culinary Science Reference Standard Check the assumptions and limitations against your situation before relying on the estimate.

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