Rainwater
Rainwater Harvesting Calculator
Rainwater you can collect from a roof, from your local rainfall and roof area.
litres = roof area (m²) × rainfall (mm) ×…
Also called roof water collection · rainwater collection calculator
Energy & Environment · 6 calculators
Rainwater Calculators
Rainwater harvesting from roofs, rainfall volume, tank sizing, stormwater runoff and water demand.
Rainwater
Rainfall Volume Calculator
Volume of water falling on any area from a given depth of rainfall.
litres = area (m²) × rainfall (mm) × runo…
Also called rain volume calculator · mm of rain to litres
Rainwater
Rainwater Tank Size Calculator
Storage tank size for rainwater harvesting, balancing supply against demand.
tank = min(dry-spell demand, one month of…
Also called water butt size · rainwater storage sizing
Rainwater
Runoff Calculator
Surface water runoff from a site using the rational method, for drainage design.
Q = C × i × A (rational method)
Also called surface water runoff · rational method calculator
Rainwater
Water Demand Calculator
Non-potable water demand for toilets, laundry and the garden — the rainwater-suitable uses.
demand = Σ (non-potable uses per day)
Also called non potable demand · rainwater demand calculator
Rainwater
Water Tank Volume Calculator
Capacity of a rectangular, cylindrical or horizontal tank in litres and gallons, with fill levels.
Rectangular V = l × w × h
Also called tank capacity calculator · water storage volume
Key rainwater formulas
| Rainwater Harvesting | litres = roof area (m²) × rainfall (mm) × runoff coefficient × filter efficiency |
|---|---|
| Rainfall Volume | litres = area (m²) × rainfall (mm) × runoff coefficient |
| Rainwater Tank Size | tank = min(dry-spell demand, one month of average supply × 1.5) |
| Runoff | Q = C × i × A (rational method) |
| Water Demand | demand = Σ (non-potable uses per day) |
| Water Tank Volume | Rectangular V = l × w × h · Cylinder V = πr²h · 1 m³ = 1,000 litres |
Rainwater questions
How much water does 1 mm of rain give?
One litre per square metre of roof — so 10 mm on a 100 m² roof is 1,000 litres before losses.
How many litres in a cubic metre?
Exactly 1,000 litres. One litre of water weighs one kilogram.