Water Tank / Sump Capacity Calculator

The right tank is not the biggest tank - it is the one that matches your household and your supply. Four people in a flat with daily municipal supply need far less storage than the same family on a farm with a tanker that visits every other day.

Water Tank / Sump Capacity Calculator works from the demand side: number of residents and guests, per-person consumption for the usage type, and the number of days of storage you want. It reports the recommended capacity in litres, cubic metres and gallons for both the overhead tank and the underground sump, plus a suggested cylindrical dimension.

Usage presets cover standard houses, apartments, villas and high-consumption homes, and the storage-days input models anything from daily supply to deep reserve. Everything runs in the browser; nothing is uploaded.

• Demand-first sizing: Residents and per-capita usage drive the answer, not a guess.
• Usage presets: Apartment, standard house, villa and high-consumption rates.
• Two-tank model: Separate overhead and sump capacities shown side by side.
• Storage days: Model daily supply to multi-day reserves for intermittent mains.
• Multi-unit support: Enter apartments or floors sharing one building tank.
• Unit output: Litres, cubic metres and gallons in every read.
• Suggested dimensions: A cylindrical tank height/diameter combination to visualise the size.
• Converter: Litres, m3, ft3 and gallons in one screen.
• Export: Copy or download the sizing as text, CSV or JSON.
• Learning guide: Demand math, pump sizing and how to store safely.

1. Enter the number of residents and any frequent guests.
2. Pick the usage type - apartment, standard house, villa or high-consumption - which sets the litres per person per day.
3. Set storage days for the overhead tank (usually 1) and for the sump (usually 2-3, more if supply is intermittent).
4. Review the daily requirement and the recommended capacities in litres, m3 and gallons.
5. Check the suggested tank dimensions to visualise the size.
6. Use the converter tab for litres, m3, ft3 and gallons.
7. Export the sizing for your plumber or builder.

Example 1 - Standard family. 4 people at 150 L/person/day = 600 L daily. An overhead tank of 600-800 L and a sump of 1,200-1,800 L covers a 2-3 day reserve.

Example 2 - Villa with garden. 5 people at 200 L/person/day = 1,000 L daily; a garden adds 500 L more. Plan a 1,500 L overhead and a 3,000-4,500 L sump.

Example 3 - Apartment block. 3 floors x 4 residents at 135 L/day = 1,620 L daily. The building tank table handles units directly.

Example 4 - Intermittent supply. Daily need 600 L with supply every 3 days: sump 1,800 L plus the 600 L overhead buffer.

Example 5 - Dimension check. A 1,620 L tank at 2 m high cylinders to about 1.0 m diameter - the converter shows litres to m3 in one step.

• Size to demand, not to folklore: Residents and usage pick the tank, not the neighbour.
• Two tanks, one answer: Overhead and sump sized together so the system works as one.
• Outage-proofing: Storage days model everything from daily mains to tanker schedules.
• Multi-unit ready: Floors and apartments add to the building tanks correctly.
• Unit clarity: Litres, m3, gallons and a visual dimension in every output.
• Export-ready: Text, CSV and JSON for the plumber, builder or municipality form.
• Free and private: No uploads, no accounts, no logging.