Ratio Calc is a quick and easy tool for radio control car racers to use trackside. Knowing your final drive ratio (FDR) is very useful for comparison with other racers to determine if your car is geared correctly. You can also view your favourite information on Apple Watch.

It lets you quickly select your car by filtering on manufacturer and model. Select your pinion and spur size and the FDR is displayed. Tyre diameter can also be entered to calculate your rollout.

Ratio and roll out charts are also available which plot pinion and spur gear combinations to create very handy reference tables.

- Save your favourite cars for quick access

- Save notes and track name against your favourite cars

- Share ratio/rollout charts

- Download new cars from within the app

- Select measurement units (imperial/metric)

- Select your preferred gear pitch, alternative ratios in other pitches will be shown

- Over 1600 cars/variants in the database

What’s New

Version 6.6

-Support for the latest devices and iOS
-Improved the database update process to show more details
-Removed the text erasing buttons on the text fields when editing notes
-Moved the gear and diameter pickers up so that the results can be seen whilst changing the settings
-Updated database and manufacturers
-Various other little tweaks and improvements

Enjoy your R/C racing!

Ratings and Reviews

5.0 out of 5
6 Ratings

6 Ratings

I-Smithy07 ,

Great app

Found this a great app and does what says has most cars as well

Shunt69 ,

Ratio Calc

Spot on have recommend this app to all who would listen at our RC club

Ratio calc 123456 ,

Great app

Great app helped with all my gearing problems

App Privacy

The developer, David Mills, has indicated that the app’s privacy practices may include handling of data as described below. For more information, see the developer’s privacy policy.

Data Not Collected

The developer does not collect any data from this app.

Privacy practices may vary based on, for example, the features you use or your age. Learn More


  • Family Sharing

    Up to six family members will be able to use this app with Family Sharing enabled.

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