Rainwater Harvesting Calculator
Calculate how much rainwater you can collect from your roof based on rainfall, roof size, and efficiency. Get instant results and estimate water savings.
Rainwater Harvesting Calculator – Estimate Your Water Collection
Have you ever wondered how much rainwater you can collect from your roof? This rainwater calculator helps you quickly estimate how much water you can capture and reuse.
What Is a Rainwater Harvesting Calculator?
A rainwater harvesting calculator estimates how much water can be collected from a surface like a roof using rainfall, area, and efficiency.
Rainwater Harvesting Formula Explained
Rainfall × Catchment Area × Efficiency
- Rainfall: Annual precipitation (mm)
- Area: Roof size (m²)
- Efficiency: Usually 0.75–0.9
Example Calculation
Roof: 100 m² | Rainfall: 800 mm | Efficiency: 0.8
800 × 100 × 0.8 = 64,000 liters/year
Alternative Methods
Metric
Rainfall (mm) × Area (m²)
US Formula
0.623 × sq ft × inches
How to Use the Calculator
- Enter roof area
- Enter rainfall
- Select roof type
- Click calculate
Factors That Affect Collection
- Roof size
- Rainfall
- Roof material
- System efficiency
Benefits of Rainwater Harvesting
- Save money
- Reduce water usage
- Eco-friendly
- Lower runoff
Tank Size Tips
- Store 1–3 months of water
- Adjust for rainfall patterns
- Match usage needs
Common Mistakes
- Ignoring efficiency
- Wrong rainfall data
- Overestimating storage
FAQ
How do I calculate rainwater collection?
Multiply rainfall × area × efficiency.
How much rainwater can I collect?
Depends on roof size and rainfall.
What is efficiency?
Usually 75–90% depending on roof type.
Is rainwater safe?
Yes for gardening; filtration needed for drinking.
Can I use this worldwide?
Yes, just enter local rainfall.