Rain Catcher Calculator

Measure your roof on the map, and see what size rainwater tank it can fill — and how long that water lasts through the dry season.

1 · Measure your roof

satellite

2 · Roof sections

m²
Roof type sets the runoff loss (first-flush, evaporation). Metal/tile catches the most.

3 · How you’ll use the water

demand
95 L
— L/day

Your roof & tank

live
Total catchment 0 m²

Your harvest plan

results

Month-by-month water balance

—
Rain collected Water used Tank level (% full)
Rainfall normals: Climates to Travel · 1991–2020 (Krabi 1981–2010, Jakarta 1991–2006)

Tank geometries to consider

ideas

Same volume, very different architecture.

Round ferrocement
6.3 m³ · Ø2.0 × 2.0 m
The workhorse.
Slimline wall tank
1.6 m³ · 2.0 × 0.45 × 1.8 m
Hugs a wall.
Modular IBC stack
4.8 m³ · 4 × 1.0 × 1.2 × 1.0 m
Off-the-shelf totes.
Elevated gravity tower
2.5 m³ · Ø1.4 × 1.6 m · +3 m
Gravity-fed, no pump.
Underground cistern
12.5 m³ · 2.5 × 2.5 × 2.0 m
Hidden and cool.
Stepped terrace
2.3 m³ · 3 × 1.6 × 0.8 × 0.6 m
Storage as landscape.
Monthly rainfall figures are long-term climatological normals (1991–2020 for most cities; Krabi 1981–2010, Jakarta 1991–2006), compiled by Climates to Travel from national meteorological-service data. These are long-term averages — actual year-to-year rainfall varies, so substitute local rain-gauge data for a precise plan. Tank sizing targets ~90% of demand met from rain in an average year. 1 mm of rain on 1 m² of roof ≈ 1 litre. Source: Climates to Travel.