# O vs Hydraulic

The clearest difference is in-app purchases: O at none against Hydraulic's 2. O also leads on review sentiment (83% vs 50%) and iOS requirement (12.1 vs 15.1). Hydraulic's advantage is rating (4.1 vs 3.8) and ratings volume (17 vs 5). On price, update cadence, ads and device support there is nothing between them.

Both are free to download. Hydraulic sells 2 one-off in-app purchases. O asks for nothing beyond the download.

Hydraulic holds the better App Store score, 4.1 against 3.8. Both are backed by a comparable volume of ratings — 5 and 17 respectively. Written reviews complicate that: 83% of O's written reviews are positive against 50% of Hydraulic's, so the app with the better star average is not the one people write more warmly about.

O ships an update every 3 months, Hydraulic every 6 weeks. The most recent releases landed on October 12, 2026 and October 20, 2026 respectively.

## The numbers

| Metric | O | Hydraulic |
| --- | --- | --- |
| Price | Free | Free |
| Rating | [3.8 (5 ratings)](https://appshunter.io/ios/app/o-ring/id485346224/reviews) | **[4.1 (17 ratings)](https://appshunter.io/ios/app/hydraulic-calculator/id612615039/reviews)** |
| Number of ratings | 5 | **17** |
| Positive reviews | **83.3% of reviews** | 50.0% of reviews |
| In-app purchases | **No** | Yes |
| Ads | No | No |
| Update frequency | Every 3 months | **Every 6 weeks** |
| Monetization | **Free** | Free with in-app purchases |
| Size | 26 MB | 24 MB |
| Requires iOS | **12.1** | 15.1 |
| Devices | iPhone, iPad, iPod | iPhone, iPad, iPod |
| Age rating | 12+ | 4+ |
| Developer | [Trelleborg Sealing Solutions](https://appshunter.io/developer/396863758) | [Zanthic Automation Inc.](https://appshunter.io/developer/574695320) |

## What reviewers say

### O

[App page](https://appshunter.io/ios/app/o-ring/id485346224)

This app helps users calculate O-Ring dimensions and find compatible materials for their applications. It provides recommendations based on ISO standards and supports both metric and inch measurements.

**Highlights:** O-Ring housing calculation, O-Ring size recommendations by ISO standard, Quick search by national/international standards, O-Ring tolerance calculation, Metric and inch unit switching, Chemical compatibility check, Integration of Trelleborg Sealing Solutions Videos

**Features:** macOS Compatibility

**In-app purchases:** none


### Hydraulic

[App page](https://appshunter.io/ios/app/hydraulic-calculator/id612615039)

Perform essential hydraulic calculations for cylinders, pumps, and fluid lines. Solve for forces, speeds, torque, power, and pressure drop. Supports metric and imperial units, with advanced features unlocked via in-app purchase.

**Highlights:** Cylinder force and speed calculations, Pump displacement, flow, and pressure calculations, Hydraulic line fluid velocity and pressure drop, Orifice flow and pressure calculations, Speed, torque, and power calculations, Metric and imperial unit support, Copy results to clipboard

**Features:** macOS Compatibility

**In-app purchases (2)**

| Purchase | Price | Billing |
| --- | --- | --- |
| Full Version | $7.99 | one-time |
| Pro Version | $7.99 | one-time |


## Frequently asked questions

### Is O free?

O is free to download, with no in-app purchases.

### Is Hydraulic free?

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

### Which has better reviews, O or Hydraulic?

Hydraulic is rated higher. O averages 3.8 out of 5 from 5 ratings, while Hydraulic averages 4.1 from 17 ratings.

### Do O or Hydraulic have ads?

Neither O nor Hydraulic shows ads.

### Which is updated more often, O or Hydraulic?

O ships an update every 3 months, and Hydraulic every 6 weeks. Most recently, O was updated on October 12, 2026 and Hydraulic on October 20, 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.*