Sewage Flow Rate Calculator Formula
Understand the math behind the sewage flow rate calculator. Each variable explained with a worked example.
Formulas Used
Average Daily Flow
avg_daily_flow = avg_dailyPeak Hourly Flow
peak_hourly_flow = avg_daily / 24 * peak_factorPeak Minute Flow
peak_gpm = avg_daily / 24 / 60 * peak_factorVariables
| Variable | Description | Default |
|---|---|---|
occupants | Number of Occupants(people) | 50 |
per_capita_gpd | Per Capita Flow(gal/day) | 80 |
peak_factor | Peak Hour Factor | 2.5 |
avg_daily | Derived value= occupants * per_capita_gpd | calculated |
How It Works
Sewage Flow Estimation
Average Daily Flow = Occupants x Per Capita GPD
Peak Flow = Average / 24 x Peak Factor
Residential per-capita wastewater is typically 60 to 100 gallons per day. The peak-hour factor (2 to 4 for residential, up to 5 for commercial) accounts for the morning and evening surges.
Worked Example
50 occupants, 80 gal/day each, peak factor 2.5.
- 01Avg daily = 50 x 80 = 4,000 gal/day
- 02Avg hourly = 4,000 / 24 = 167 gal/hr
- 03Peak hourly = 167 x 2.5 = 417 gal/hr
- 04Peak GPM = 417 / 60 = 6.9 GPM
Frequently Asked Questions
What per-capita flow should I assume?
Residential: 60 to 100 GPD. Office buildings: 15 to 25 GPD per worker. Schools: 10 to 15 GPD per student. Restaurants: 30 to 50 GPD per seat.
Why use a peak factor?
Sewage flow is not constant throughout the day. The peak factor ensures the system can handle the busiest hour without backing up.
Ready to run the numbers?
Open Sewage Flow Rate Calculator