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 1500 cars/variants in the database

What’s New

Version 6.5

We've added a tip jar - the app has been kept up to date since 2011 and we've never charged for an update. Any tip will unlock the ability to change the app's colour scheme and app icon - we've even included some retro icons that may be familiar to long time users.

Also in this version:
-Improved watch app reliability
-Transponder input form improvements
-Other boring little fixes and optimisations

Ratings and Reviews

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

MikeMann210 ,


A really great simple to use app.
A MUST fir every electric car racer!


David Mills
8.4 MB
Requires iOS 9.0 or later. Compatible with iPhone, iPad and iPod touch.
English, German, Italian, Spanish
Age Rating
Rated 4+
© 2011-2018 David Mills
In-App Purchases
  1. Generous Tip £2.99
  2. Nice Tip £0.99


  • Family Sharing

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

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