BOD (biochemical oxygen demand) load is the mass of biodegradable organic matter discharged per unit time, usually expressed in kg/day or lb/day. It equals flow rate multiplied by BOD concentration with an appropriate unit conversion.

What is the conversion formula?

For SI units: BOD load (kg/day) = Flow (m³/day) × Concentration (mg/L) × 0.001. The factor 0.001 converts mg/m³ equivalent units to kg. For US customary: BOD load (lb/day) = Flow (MGD) × Concentration (mg/L) × 8.34.

Are mg/L and g/m³ the same?

Yes — for dilute aqueous solutions (density ≈ 1 kg/L) mg/L and g/m³ are numerically identical. Both are standard units for BOD concentration in water quality work.

What is a typical BOD concentration for municipal wastewater?

Raw municipal sewage typically ranges from 150–300 mg/L BOD. Secondary-treated effluent typically falls below 30 mg/L, and advanced treatment can achieve less than 10 mg/L.

How does BOD load differ from BOD concentration?

Concentration (mg/L) describes the strength of the wastewater. Load (kg/day) accounts for both strength and flow volume, giving the total mass of pollutant discharged. Two streams can have the same concentration but very different loads if flows differ.

BOD Load Calculator

Enter flow rate and BOD concentration to get the daily BOD mass load in kg/day or lb/day.

Inputs

Flow Rate

BOD Concentration

mg/L and g/m³ are numerically equal for water.

BOD Load

Enter values and press Calculate.

Common Conversion Factors

Flow Units	Conc. Units	Load Formula	Result Units
m³/day	mg/L	Q × C × 0.001	kg/day
L/s	mg/L	Q × 86.4 × C × 0.001	kg/day
MGD	mg/L	Q × C × 8.34	lb/day
ft³/s	mg/L	Q × 2446.58 × C × 0.001	kg/day

Summary

BOD load quantifies the mass of oxygen-consuming organic matter discharged per day in a wastewater stream. It is calculated by multiplying the volumetric flow rate by the BOD concentration and a unit-conversion factor. Environmental engineers use BOD load to size treatment plants, set discharge permits, and assess receiving-water impact.

How it works

Enter the wastewater flow rate and choose its unit (m³/day, L/s, MGD, or ft³/s).
Enter the BOD concentration and choose its unit (mg/L or g/m³ — they are numerically equal).
The calculator multiplies flow by concentration and applies the correct conversion factor.
Results are shown in both kg/day and lb/day simultaneously.
Use the reset button to clear all fields and start a new calculation.

Use cases

Size aeration tanks and secondary clarifiers for a municipal wastewater plant.
Calculate effluent BOD load for NPDES permit compliance.
Assess organic loading on a receiving river or stream.
Convert field measurements taken in different unit systems for reporting.
Compare influent and effluent BOD loads to verify treatment efficiency.
Estimate BOD load contributions from industrial dischargers.

Frequently Asked Questions

Last updated: 2026-09-30 · Reviewed by Nham Vu