# Rainfall Calculator — Water Catchment Calculator

> Physics/math tool for calculating rainwater harvest volume and cost savings. (iPhone/iPad app by Tan Chia Ling.)

- Source: https://appshunter.io/ios/app/rainfall-calculator/id1446150880 (this page in markdown: same URL + `.md`)
- Developer: [Tan Chia Ling](https://appshunter.io/developer/321121189)
- Category: Productivity, Utilities
- Price: $2.99
- Rating: 5.00/5 from 1 App Store ratings
- Age rating: 4+
- Requires: iOS 13 · 1 MB
- Languages: American English
- Released: 2018-12-16
- Data updated: 2026-07-07
- Monetization: paid
- User reviews in markdown: https://appshunter.io/ios/app/rainfall-calculator/id1446150880/reviews.md

## What is Rainfall Calculator?

The Rainfall Calculator is a physics/math tool designed to help you determine how many liters/gallons of rainwater you can harvest per year, evaluate cost savings, and recommend the minimum tank size for water storage.

Features:
- Instant calculation.
- Results can be copied to other apps.
- Includes formula references.
- Supports up to 16 decimal places.
- Supports various units for each input.
- Works seamlessly on both iPhone and iPad.
- Lightweight, compact app optimized for everyday use.
- Ad-free and built with privacy in mind.

Rainwater Collection Calculator:
- The catchment area is multiplied by the depth of rain that falls on it to give the total volume of water produced.
- 1 millimeter of rain over 1 square meter of roof equals 1 liter of water.
- Annual rainfall (in millimeters) x Roof surface area (in square meters) = Roof catchment capacity.
- You can add the cost of mains or tap water per m³ to evaluate the annual cost savings if this rainwater is collected and used instead of drinking water.
- The minimum tank size should store 33% of the "Annual Rainfall On Your Roof Area" as you will use the water while you are collecting it.

The rain will collect in gutters that channel the water into downspouts and then into some sort of storage vessel. Rainwater collection systems can be as simple as collecting rain in a rain barrel or as elaborate as harvesting rainwater into large cisterns to supply your entire household demand. You can also collect rainwater for garden use. Plants prefer rainwater because it's naturally soft and free of chlorine and other chemicals. If drought is a problem where you live, collecting rainwater is a good way to handle watering restrictions. If you're on a municipal water system, you can save a considerable amount of money.

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## Key features

- Instant rainwater calculation
- Cost savings evaluation
- Minimum tank size recommendation
- Supports various input units
- Formula references included
- Results copyable to other apps


## Frequently asked questions about Rainfall Calculator

### What is the Rainfall Calculator used for?

Rainfall Calculator is a physics and math tool designed to help users determine the volume of rainwater they can harvest annually, evaluate potential cost savings compared to mains water, and recommend the appropriate size for water storage tanks.

### How does Rainfall Calculator determine water volume?

It calculates water volume by multiplying the catchment area (e.g., roof surface area in square meters) by the depth of rain that falls on it (in millimeters). The app provides formula references for clarity.

### Can Rainfall Calculator help me save money?

Yes, the app allows you to input the cost of mains or tap water per cubic meter. It then calculates the annual cost savings you could achieve by collecting and using rainwater instead of purchasing tap water.

### What is the recommended tank size?

The app recommends a minimum tank size that can store 33% of the 'Annual Rainfall On Your Roof Area'. This ensures you have enough stored water to use while collection is ongoing.

### Does Rainfall Calculator support different units?

Yes, the app supports various units for each input, providing flexibility for users worldwide. It also supports calculations up to 16 decimal places for high precision.

### Is Rainfall Calculator available on multiple devices?

Rainfall Calculator works seamlessly on both iPhone and iPad. It is designed to be a lightweight and compact app optimized for everyday use on these iOS devices.

### Does Rainfall Calculator have ads?

No, Rainfall Calculator is ad-free. The developer has built the app with privacy in mind and aims to provide an uninterrupted user experience.

### How often is Rainfall Calculator updated?

The latest version of Rainfall Calculator is 1.3, last updated on February 28, 2026. While specific update frequency isn't detailed, this indicates ongoing support and development.

## Version history (last 4 releases)

### 1.3 — 2026-02-28

- Updated for the newest devices.
- Minor bugs fixed.

### 1.2 — 2024-07-08

- Updated for the newest devices.
- Minor UI update.
- Minor bugs fixed.

### 1.1 — 2021-05-05

- Update for Newest Devices
- Bug Fixed

### 1.0 — 2018-12-15

No release notes.

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## More apps by Tan Chia Ling

- [Coloring Book - Plus](https://appshunter.io/ios/app/coloring-book-plus/id500418548)
- [Resistor Plus](https://appshunter.io/ios/app/resistor-plus/id500615686)
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- [Gold Luxury Clock](https://appshunter.io/ios/app/gold-luxury-clock/id505043266)
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- [Premium Clock](https://appshunter.io/ios/app/premium-clock/id517487778)

All apps by Tan Chia Ling: https://appshunter.io/developer/321121189

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*Data collected daily from the US App Store and indexed by [AppsHunter](https://appshunter.io/). User reviews are verbatim App Store reviews. Ratings, prices and chart positions refresh continuously; this snapshot is from 2026-07-07.*