# Hydrology Formulator vs Activity Block

The clearest difference is price: Hydrology Formulator at Free against Activity Block's $0.99. Hydrology Formulator also leads on update cadence (every 6 months vs every 14 months). Activity Block's advantage is in-app purchases (none vs 1) and iOS requirement (16.4 vs 18.6). On ads and device support there is nothing between them.

Hydrology Formulator is free to download; Activity Block costs $0.99 up front. Hydrology Formulator sells 1 one-off in-app purchase. Activity Block asks for nothing beyond the download.

Hydrology Formulator ships an update every 6 months, Activity Block every 14 months. The most recent releases landed on October 8, 2026 and October 7, 2026 respectively.

## The numbers

| Metric | Hydrology Formulator | Activity Block |
| --- | --- | --- |
| Price | **Free** | $0.99 |
| Rating | **[5.0 (1 ratings)](https://appshunter.io/ios/app/hydrology-formulator/id346512904/reviews)** | — |
| Number of ratings | **1** | — |
| Positive reviews | 0.0% of reviews | — |
| In-app purchases | Yes | **No** |
| Ads | No | No |
| Update frequency | **Every 6 months** | Every 14 months |
| Monetization | Free | — |
| Size | 18 MB | 1 MB |
| Requires iOS | 18.6 | **16.4** |
| Devices | iPhone, iPad | iPhone, iPad |
| Age rating | 4+ | 4+ |
| Developer | [Historycentral.com](https://appshunter.io/developer/1744330560) | [Luciano Souto](https://appshunter.io/developer/945191416) |

## What reviewers say

### Hydrology Formulator

[App page](https://appshunter.io/ios/app/hydrology-formulator/id346512904)

This app provides a comprehensive collection of over 1,000 formulas, calculators, and conversions for hydrology and civil engineering. It covers a wide range of topics including groundwater, stormwater, pipe flow, and water pollution.

**Highlights:** 1,000+ formulas and calculators, Groundwater analysis tools, Stormwater design calculations, Open channel and pipe flow equations, Water pollution modeling, Conversions and reference data

**Features:** macOS Compatibility, Vision Pro support

**In-app purchases (1)**

| Purchase | Price | Billing |
| --- | --- | --- |
| Pro Version | $3.99 | one-time |


### Activity Block

[App page](https://appshunter.io/ios/app/activity-block/id6474466722)

**Features:** macOS Compatibility

**In-app purchases:** none


## Frequently asked questions

### Is Hydrology Formulator free?

Hydrology Formulator is free to download, with in-app purchases available.

### Is Activity Block free?

Activity Block costs $0.99, with no in-app purchases.

### Do Hydrology Formulator or Activity Block have ads?

Neither Hydrology Formulator nor Activity Block shows ads.

### Which is updated more often, Hydrology Formulator or Activity Block?

Hydrology Formulator ships an update every 6 months, and Activity Block every 14 months. Most recently, Hydrology Formulator was updated on October 8, 2026 and Activity Block on October 7, 2026.

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*Compared by [AppsHunter](https://appshunter.io/) from daily US App Store data. Review summaries are generated from verbatim App Store reviews.*