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WATER / ROOF HARVEST

Rainwater Tank Sizing Calculator

Compare roof-harvest yield with entered storage-period demand to estimate a bounded rainwater-tank planning capacity.

  • 01 Calculated in this tab
  • 02 Values stay in this browser tab
  • 03 Use boundary

Conversion input

Known value

Filter by unit name, symbol, or code. Your current selections remain available.

Inputs

Allowance and efficiency

Inputs

Preparing the calculator...

Use boundary

Calculation path

Roof square metres times rainfall millimetres gives litres before runoff loss; capacity is bounded by harvest and entered demand.

Calculation path

Harvest litres = roof m² x rainfall mm x runoff fraction; planning capacity is limited by entered demand and harvest.

What you provide

What you provide

  • Effective roof catchment: Horizontal catchment area contributing to the collection system.
  • Design-period rainfall: Rainfall depth for the same modeled storage period.
  • Collection efficiency: Share reaching storage after first flush, splash, and system loss.
  • Storage period: Number of demand days represented by the rainfall period.
  • Daily rainwater demand: Average intended non-potable or treated-water use.

What you receive

What you receive

  • Planning tank capacity
  • Estimated harvest available
  • Demand over the selected period

Use boundary

Choose the maximum decimal places shown. This does not increase source accuracy.

Use local rainfall sequences, dry spells, first flush, overflow, treatment, potable-water rules, and structural requirements for design.

Planning and fitness outputs are estimates. Confirm measurements, product specifications, site conditions, health context, and professional requirements before making purchasing, training, medication, or care decisions.

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