# Propeller Calc vs FUEL DENSITY

The clearest difference is price: Propeller Calc at Free against FUEL DENSITY's $2.99. FUEL DENSITY's advantage is update cadence (every 5 days vs every 21 months) and iOS requirement (15.2 vs 17.0). On ads, in-app purchases and device support there is nothing between them.

Propeller Calc is free to download; FUEL DENSITY costs $2.99 up front. Neither carries in-app purchases, so what you see is what you pay.

Propeller Calc ships an update every 21 months, FUEL DENSITY every 5 days. The most recent releases landed on September 26, 2026 and October 8, 2026 respectively.

## The numbers

| Metric | Propeller Calc | FUEL DENSITY |
| --- | --- | --- |
| Price | **Free** | $2.99 |
| Rating | **[3.0 (1 ratings)](https://appshunter.io/ios/app/propeller-calc/id478119478/reviews)** | — |
| Number of ratings | **1** | — |
| Positive reviews | 100.0% of reviews | — |
| In-app purchases | No | No |
| Ads | No | No |
| Update frequency | Every 21 months | **Every 5 days** |
| Monetization | Free | — |
| Size | 3 MB | 2 MB |
| Requires iOS | 17.0 | **15.2** |
| Devices | iPhone, iPad | iPhone, iPod |
| Age rating | 4+ | 17+ |
| Developer | [Frode Rørvik](https://appshunter.io/developer/478119481) | [Oleksii Nezhalskyi](https://appshunter.io/developer/1687730603) |

## What reviewers say

### Propeller Calc

[App page](https://appshunter.io/ios/app/propeller-calc/id478119478)

This utility calculates propeller performance metrics like pitch, gear ratio, RPM, slip, and speed. Input any four values, and the app computes the fifth, helping users understand the relationship between propeller design and boat performance.

**Highlights:** Calculate pitch, gear ratio, RPM, slip, and speed, Enter any four variables to find the fifth, Understand propeller slip and its impact, Supports iPhone and iPad, Free to use

**Features:** macOS Compatibility

**In-app purchases:** none


### FUEL DENSITY

[App page](https://appshunter.io/ios/app/fuel-density/id6450055630)

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

**In-app purchases:** none


## Frequently asked questions

### Is Propeller Calc free?

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

### Is FUEL DENSITY free?

FUEL DENSITY costs $2.99, with no in-app purchases.

### Do Propeller Calc or FUEL DENSITY have ads?

Neither Propeller Calc nor FUEL DENSITY shows ads.

### Which is updated more often, Propeller Calc or FUEL DENSITY?

Propeller Calc ships an update every 21 months, and FUEL DENSITY every 5 days. Most recently, Propeller Calc was updated on September 26, 2026 and FUEL DENSITY on October 8, 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.*