What is a Sump Drainage Tank?
A sump tank is a low-level pit or underground basin designed to collect excess rainwater, groundwater runoff, or wastewater before it is pumped out by an automated sump pump. Proper sump sizing prevents basement flooding and storm overflow.
For drainage guidelines, reference USGS Water Storage Guidelines.
Sump Tank Volume Formulas
Rectangular Concrete Sump:
Volume (V) = Length × Width × Depth
Litres Formula:
Capacity (Litres) = Length (m) × Width (m) × Depth (m) × 1,000
How to Calculate Sump Capacity
- Measure Internal Length & Width: Measure inside pit wall dimensions.
- Measure Usable Depth: Record depth from pit bottom to top overflow / pump cut-off line.
- Calculate Volume: Multiply length × width × depth.
- Convert to Storage Units: Convert cubic meters to Litres or Gallons.
Sump Numerical Example
For a rectangular basement sump pit measuring 8 ft long, 6 ft wide, and 5 ft deep:
Volume = 8 × 6 × 5 = 240 ft³Capacity in US Gallons = 240 × 7.48052 ≈ 1,795.32 US GallonsCapacity in Litres = 1,795.32 × 3.78541 ≈ 6,796.08 Litres
Standard Domestic Sump Pit Sizing Chart
| Sump Application | Dimensions (L × W × D) | Capacity (Litres) | Capacity (US Gal) |
|---|---|---|---|
| Basement Drainage Pit | 0.6m × 0.6m × 0.8m (2ft × 2ft × 2.6ft) | 288 L | 76 gal |
| Small Residential Sump | 1.5m × 1.2m × 1.2m (5ft × 4ft × 4ft) | 2,160 L | 570 gal |
| Medium Home Concrete Sump | 2.5m × 2.0m × 1.5m (8.2ft × 6.6ft × 5ft) | 7,500 L | 1,981 gal |
| Commercial Sump Cistern | 4.0m × 3.0m × 2.0m (13.1ft × 9.8ft × 6.6ft) | 24,000 L | 6,340 gal |
Submersible Sump Pump Sizing & Freeboard Space
Always maintain a 15-20% freeboard margin above the upper float switch to handle storm water surges without flooding adjacent basements or mechanical rooms.
Sump Tank Sizing & Emergency Reserve Buffer
Sump tanks collect drainage, rainwater runoff, or process wastewater prior to pumping or treatment. When calculating required sump capacity, engineers specify a working volume between the pump activation switch and high-water alarm, plus a emergency reserve capacity buffer to handle power outages or pump failures. Regular inspection and clearing of sediment maintain usable sump volume.