Free water and wastewater math calculators
Each calculator shows its steps, so you can check your own work on practice problems. They use the same conversion factors as most exam reference sheets: 8.34 lbs/gal, 7.48 gal/ft³ and 0.785 × D².
- Pounds Formulalbs/day = Flow (MGD) × Concentration (mg/L) × 8.34 lbs/gal
- Detention TimeDetention time (hr) = Tank volume (gal) ÷ Flow (gal/hr)
- F/M RatioF/M = (Flow MGD × BOD mg/L × 8.34) ÷ (Aeration volume MG × MLVSS mg/L × 8.34)
- MCRT / Sludge AgeMCRT (days) = lbs solids in aeration + clarifier ÷ (lbs/day WAS + lbs/day effluent TSS)
- SVISVI (mL/g) = 30-min settled volume (mL/L) × 1,000 ÷ MLSS (mg/L)
- Chlorine Dose and FeedDose (mg/L) = Demand + Residual
- Surface Overflow RateSOR (gpd/ft²) = Flow (gpd) ÷ Surface area (ft²)
- Weir Overflow RateWOR (gpd/ft) = Flow (gpd) ÷ Weir length (ft)
- Percent Removal% Removal = (In − Out) ÷ In × 100
- Pipe VolumeVolume (gal) = 0.785 × (D in ÷ 12)² × Length (ft) × 7.48
- Flow Rate (Q = A × V)Q (ft³/s) = A (ft²) × V (ft/s)
- CT ValueCT (mg·min/L) = Residual (mg/L) × Contact time (min)