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Rain Harvest Calculator

Lifestyle Tools

Roof × rainfall × runoff, annual yield

Quick Answer

Rain Harvest Calculator: Roof × rainfall × runoff, annual yield. Rain Harvest Calculator uses standard everyday life formulas to compute accurate results instantly.

Catchment

m²
mm
mm
m³
Collectable per rainfall2.9 m³（2,916 L）
Annual yield (after first flush)77.2 m³
Days covered5.8 d
Runoff coefficientψ = 0.9
First-flush factorδ = 0.9（skip first 2-3 mm）

How it works (GB 50400-2016)

  1. 1Single = area × rain ÷ 1000 × ψ × δ = 2.92 m³
  2. 2Annual = area × annual ÷ 1000 × ψ × 0.65 = 77.2 m³
  3. 3Days = 2.92 ÷ 0.5 = 5.8 d
  4. 4Size tank ≥ single yield, cross-check with 3-day reuse demand

GB 50400-2016 runoff coefficients: roof 0.90-0.95, paved 0.80-0.90, green 0.10-0.20; first flush of 2-3 mm must be diverted.

Rain harvesting is efficient only where annual rainfall exceeds ~400 mm; cities above ~800 mm should prioritize roof catchment.

Design volume = min(rainfall method, water-balance method); stored rainwater should be used or infiltrated within 3 days.

Typical reuse demand: irrigation 0.3 m³ per 100 m² per day, road washing 0.2 m³ per 100 m² per day.

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How to Use

  1. Enter scenario values: fill real-life numbers into the Rain Harvest Calculator (defaults work for a quick try).
  2. Instant results: everything computes live, no button needed.
  3. Read the advice: results come with practical tips, reference standards and pitfalls.
  4. Compare options: adjust parameters to compare choices side by side.

Key Points

  • Rain Harvest Calculator is a free online everyday life tool — open and use, no sign-up.
  • All calculations run locally in your browser; your data never leaves the device.
  • Key capability: Roof × rainfall × runoff, annual yield.
  • Results come with formulas and reference tables so you can verify every number.

Formula & How It Works

Rain Harvest Calculator formula

Rain Harvest Calculator uses standard everyday life formulas to compute accurate results instantly.

FAQ

How do I use the Rain Harvest Calculator?
Open the page and fill in the input fields — results update automatically. Roof × rainfall × runoff, annual yield.
Are the results accurate?
Yes. Standard formulas and conversion factors are used and verified.
Is it free? Do I need to sign up?
Completely free. No registration, login or download required.
Does it work on mobile?
Yes. The responsive design works on phones, tablets and desktops.
Is my data saved?
No. Everything runs locally in your browser.

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Source & Updates

Based on common formulas and industry conventions. Last updated: 2025-07

Last updated:

Formulas and content on this page are reviewed by the YiJianSuan team. For reference only — official sources prevail.

Maintained and periodically reviewed by the YiJianSuan editorial team — review process in ourEditorial Policy.

Cite this page: YiJianSuan. Rain Harvest Calculator[EB/OL]. https://www.yijiansuan.com/en/c/life/rain-harvest

Results provided by this tool are for reference only and do not constitute professional advice.