Rainwater Harvesting Tank Sizing Calculator
Size a rainwater harvesting tank from roof area, annual rainfall, runoff coefficient and daily water demand. Shows annual harvest, how much demand it covers and the tank volume for your dry-spell length.
Input
Demand
Output
| Property | Value |
|---|---|
| No data yet | |
More ways to use this tool
REST API
curl -X POST https://api.iotools.cloud/v1/tool/rainwater-harvesting-tank-sizing \
-H "Authorization: Bearer YOUR_API_KEY" \
-H "Content-Type: application/json" \
-d '{
"units": "metric",
"roofArea": "100",
"rainfall": "800",
"surface": "0.9",
"efficiency": "90",
"dailyDemand": "250",
"dryDays": "21"
}'Swap in your own key from your account. The tool's fields are the body — no wrapper.
Ask an AI agent
Use the IOTools `rainwater-harvesting-tank-sizing` tool (Rainwater Harvesting Tank Sizing Calculator) on this input:
YOUR_INPUT_HEREPaste this at any agent connected to the IOTools MCP server, then add your input.
Embed widget
<iframe
src="https://iotools.cloud/embed/rainwater-harvesting-tank-sizing/"
width="100%" height="520" frameborder="0" scrolling="no" loading="lazy"
title="Rainwater Harvesting Tank Sizing Calculator — iotools.cloud"
sandbox="allow-scripts allow-forms allow-same-origin allow-downloads allow-popups allow-popups-to-escape-sandbox"
allow="clipboard-write"
style="width:100%;border:1px solid #e5e7eb;border-radius:12px;overflow:hidden"></iframe>
<script src="https://iotools.cloud/embed.js" async></script>Drop this into your own page — free, no key required, just a link back.
| Cost per API/MCP call | From 5 credits |
|---|---|
| Need more credits? | View pricing |
Also available with
Guides
Estimate how much rainwater your roof can collect in a year, how much of your demand that covers, and how large a storage tank you need to bridge a dry spell.
How to use it
- Choose metric or imperial units.
- Enter the roof catchment area (the horizontal footprint, not the sloped surface) and annual rainfall.
- Pick the roof surface and set the filter / first-flush efficiency.
- Enter your daily demand and the longest dry spell you want to cover.
The formulas
- Annual harvest = area × rainfall × runoff coefficient × efficiency (1 mm of rain on 1 m² is 1 litre)
- Annual demand = daily demand × 365
- Tank size = daily demand × dry-spell days, capped at the annual harvest
Runoff coefficients
Smooth metal and glazed tile shed about 90 % of rain; asphalt and concrete a little less; porous clay tile about 75 %; gravel and green roofs only around 40 %.
Limits
This is a simple annual-average sizing, not a month-by-month mass-balance simulation. Real rainfall is seasonal, so check the result against monthly data if supply is critical.
Privacy
Everything is calculated in your browser; nothing is uploaded.