Turn site flows into reliable equivalent population numbers. Include allowances for infiltration, peaks, and safety. Export results for reports and review with teams easily.
| Scenario | Avg Flow (m³/day) | I/I (%) | BOD₅ (mg/L) | BOD₅ Load (g/day) | PE (60 g/person·day) |
|---|---|---|---|---|---|
| Residential block | 500 | 15 | 300 | 172,500 | 2,875 |
| Small mixed-use site | 180 | 10 | 250 | 49,500 | 825 |
| Industrial influence | 300 | 20 | 350 | 126,000 | 2,100 |
Population equivalent (PE) expresses organic or nutrient loading as the number of people that would generate the same daily mass. During planning, PE helps compare options, screen treatment processes, and align hydraulic and process capacities with the expected service demand. Using a pollutant basis such as BOD₅ or TSS keeps the estimate tied to measurable field data rather than occupancy alone.
Site data often arrives as m³/day, while instrumentation and temporary pumping logs may be in L/s. Converting to a common basis prevents unit drift in design reports and subcontractor submittals. The I/I allowance increases average flow to reflect wet-weather infiltration and inflow. Treat I/I as a documented assumption, ideally linked to pipe age, groundwater, and inspection findings.
Concentration (mg/L) should match the pollutant basis and sampling plan. Composite samples typically represent average conditions better than grab samples. The calculator converts concentration and adjusted flow into mass loading, then adds any separate industrial contribution in g/day. This split makes it easier to justify non-domestic loads when reviewing utility connections or tenant fit-outs.
The safety factor applies after the raw PE is computed, providing room for growth, uncertainty, and seasonal variability. Rounding up is common when PE drives equipment count or module sizing. Peak factor is reported as a peak flow check, supporting pump station and headworks sizing without changing the pollutant-based PE itself.
Example: Q = 500 m³/day, I/I = 15%, C = 300 mg/L (BOD₅), per-capita = 60 g/person·day, safety = 1.15, peak = 2.5. Adjusted flow = 575 m³/day, load = 172,500 g/day, raw PE = 2,875, design PE = 3,306, final (rounded up) = 3,306. Report peak flow = 1,437.5 m³/day (≈ 16.63 L/s) for hydraulic checks.
It is the number of people that would produce the same daily pollutant mass as your measured load. It is used to size treatment processes, compare scenarios, and document design capacity assumptions.
Choose the parameter that governs your design standard or permit basis. BOD₅ is common for organic loading, TSS for solids handling, and TN/TP when nutrient limits drive process selection.
Because 1 m³ equals 1,000 L. Multiplying mg/L by m³/day converts to mg/day, and dividing by 1,000 converts mg to g. The result is g/day without extra constants.
Use condition data where possible: CCTV, groundwater level, pipe material, and wet-weather monitoring. If unknown, start with a conservative planning value and refine after surveys or commissioning measurements.
Add the extra mass as g/day when you have a known process discharge, tenant profile, or a load estimate from similar facilities. This keeps the calculation transparent versus inflating concentration values.
Most projects use one to cover uncertainty, growth, and operational variability. Align the factor with your client’s standard and regulatory guidance. If you already apply conservatism elsewhere, document the rationale for a lower factor.
It reports peak flow for hydraulic sizing of pumps, screening, channels, and headworks. It does not change the pollutant-based PE, but it helps verify that hydraulics and process sizing remain consistent.
Important Note: All the Calculators listed in this site are for educational purpose only and we do not guarentee the accuracy of results. Please do consult with other sources as well.