Rainwater Harvesting Calculator
See how much rain your rooftop can harvest in a year. Enter the roof (catchment) area, your city’s rainfall and the roof type to get the annual harvestable water — the rain that would otherwise run down the drain.
Use the roof’s plan (footprint) area for catchment — rain falls on the horizontal projection.
= 99 kilolitres · about 271 L per day averaged.
You will not catch every drop — a first-flush diverter and filter come before the tank, and overflow goes to a recharge pit. Storage vs ground-recharge is a design choice; see the rainwater harvesting guide.
A planning estimate. Actual yield depends on the rainfall pattern (a few intense spells vs steady rain), losses, first-flush and filter efficiency, and your storage size. Many Indian cities and states mandate rainwater harvesting — rules and rebates vary by location and change, so check your local by-laws. Size the system with a plumber or rainwater-harvesting specialist.
Related Guides — Deep-dive reading
Rooftop Rainwater Harvesting
The rain that lands on your roof is a free water supply and, in most Indian cities, a legal duty. What a rooftop rainwater harvesting system is, the two paths (store it for reuse or recharge the groundwater), the parts that make it work, how much a roof can actually collect, and the maintenance that keeps it honest. Plain language, India-grounded.
RoofingRooftop Rainwater Harvesting in India: Catching Rain Off Your Roof for Storage or Recharge
A homeowner's guide to rooftop rainwater harvesting — using the roof as a catchment, sizing gutters and downpipes for your area and rainfall, first-flush and filtration, and where the water finally goes: a storage sump for use or a recharge structure for the ground.
PlumbingRainwater Harvesting Guide for India: Catchment, Storage, Recharge & Bye-laws
The section pillar for rainwater harvesting — why it matters for water security and groundwater, the full catchment-to-store-or-recharge chain, the two paths of using rain versus recharging aquifers, indicative yield and sizing, first-flush and filtration, maintenance, and the mandatory-RWH reality in Indian cities.
PlumbingRelated Tools — You may also find these useful
Roof Area Calculator
The true (sloped) surface area of a roof from its plan footprint and pitch, in m² and sq ft, with a wastage allowance and rough tile/sheet/coating counts — the area you actually buy roofing materials for.
RoofingRoof Heat Gain Calculator
How much heat your roof lets in and how much insulation cuts it — heat gain in watts and the AC tonnage it adds, from roof construction (U-value), area and temperature difference, versus a bare slab.
RoofingRoof Pitch Calculator
Convert a roof's pitch between degrees, the rise-in-12 ratio (like 4:12), percentage grade and the slope (area) factor — or work the pitch out from rise and run.
Roofing