# Hydrology Formulator vs sSLOPE

The clearest difference is price: Hydrology Formulator at Free against sSLOPE's $3.99. Hydrology Formulator also leads on rating (5.0 vs 4.0) and update cadence (every 6 months vs every 27 months). sSLOPE's advantage is in-app purchases (none vs 1) and iOS requirement (15.6 vs 18.6). On ratings volume, ads and device support there is nothing between them.

Hydrology Formulator is free to download; sSLOPE costs $3.99 up front. Hydrology Formulator sells 1 one-off in-app purchase. sSLOPE asks for nothing beyond the download.

Hydrology Formulator holds the better App Store score, 5.0 against 4.0. Both are backed by a comparable volume of ratings — 1 and 1 respectively.

Hydrology Formulator ships an update every 6 months, sSLOPE every 27 months. The most recent releases landed on July 15, 2026 and September 23, 2026 respectively.

## The numbers

| Metric | Hydrology Formulator | sSLOPE |
| --- | --- | --- |
| Price | **Free** | $3.99 |
| Rating | **[5.0 (1 ratings)](https://appshunter.io/ios/app/hydrology-formulator/id346512904/reviews)** | [4.0 (1 ratings)](https://appshunter.io/ios/app/sslope/id1403201500/reviews) |
| Number of ratings | 1 | 1 |
| Positive reviews | 0.0% of reviews | — |
| In-app purchases | Yes | **No** |
| Ads | No | No |
| Update frequency | **Every 6 months** | Every 27 months |
| Monetization | **Free** | Paid |
| Size | 18 MB | 4 MB |
| Requires iOS | 18.6 | **15.6** |
| Devices | iPhone, iPad | iPhone, iPod |
| Age rating | 4+ | 4+ |
| Developer | [Historycentral.com Inc](https://appshunter.io/developer/1744330560) | [Roozbeh Geraili Mikola](https://appshunter.io/developer/1403201499) |

## 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 |


### sSLOPE

[App page](https://appshunter.io/ios/app/sslope/id1403201500)

Perform quick slope stability analyses on your mobile device. This app uses the simplified Bishop method to calculate the Factor of Safety for soil and rock slopes, supporting various conditions like water tables, external loads, and seismic forces.

**Highlights:** Analyze horizontally layered soil slopes (up to 7 layers), Incorporate water table effects and ponded water, Apply vertical external loading, Model pseudo-static seismic loads, Simulate End Anchored and Soil Nail support, Adjust failure surface search limits, Utilize Mohr-Coulomb and Hoek-Brown strength criteria, Generate and email PDF reports

**In-app purchases:** none


## Frequently asked questions

### Is Hydrology Formulator free?

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

### Is sSLOPE free?

sSLOPE costs $3.99, with no in-app purchases.

### Which has better reviews, Hydrology Formulator or sSLOPE?

Hydrology Formulator is rated higher. Hydrology Formulator averages 5.0 out of 5 from 1 ratings, while sSLOPE averages 4.0 from 1 ratings.

### Do Hydrology Formulator or sSLOPE have ads?

Neither Hydrology Formulator nor sSLOPE shows ads.

### Which is updated more often, Hydrology Formulator or sSLOPE?

Hydrology Formulator ships an update every 6 months, and sSLOPE every 27 months. Most recently, Hydrology Formulator was updated on July 15, 2026 and sSLOPE on September 23, 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.*