Making the best Ruler app for Android

Whit over 2.8 million downloads, Ruler App is the most popular measuring application on Google Play. I created the app in 2013 and 4 years later it is used by so many people because of its simplicity and accuracy. In this article, I will explain how I created it and what decisions I have made.

Why Ruler App is so great?

Here follow the most impressive features.

The design

The best thing is definitely its design. It is really fantastic. It is both elegant and intuitive while making a truly immersive experience. And the proof about all this is other similar apps that made the same interface. View it in the screenshot gallery.

The accuracy

Another thing is its accuracy. It is very hard to make an accurate on-screen ruler on Android. There are so many devices and a lot of them do not report properly dots-per-inch property, so it is impossible to draw the units correctly. Later I’ll explain more about this topic and the solution I found.

The history

I created the most advanced history of measurements functionality.  You can view lengths you took and when you took them, but also you can restore them to the ruler, set a title (for example, “box width”), copy it, share it or delete it.

The themes

In version 2.0 I’ve introduced support for themes so you can change the way app looks. Some of the different skins are free and others are available for small, one-time payment through in-app purchase. So you want a “pirate” ruler or more “space”-like outlook, you have it.

Extremely small size

After all updates of built components, after adding themes and payments, the application download size is still 1.69 MB, which is really small. For example, most popular titles are 50 MB or more. It is perfect for slow connections and for phones with minimal internal storage. I’ve made this by optimizing every image and removing large support libraries.

Other stuff

Of course, I support centimeters (cm) and inches. Inches are displayed as fractions. And of course, this app is free.


How this screen ruler is so accurate on so many devices?

As I said earlier, it is hard to build an accurate ruler for Android. A common solution is to make calibration functionality but it is not effective and users actually expect to have pre-calibrated and ready to use application.

To support so many devices I created a large database of screen dots-per-inch. When the user downloads and starts the software, this database is being checked and the most appropriate size is found.

What technology is used?

Well, obviously I use Android SDK with Java. For analyzing the traffic I use Firebase Analytics. For saving the history I use a custom solution that saves data as JSON file.

What users say?

Well, the app has 21,000+ ratings and 4,700+ reviews. The average rating is 4.3, so I am pretty proud. Users don’t need any “how to use” guide, they just know how it works. Here are some great reviews:

Very accurate, and useful to work on my physical science paper.
Amazing and functional app, you have my recommendation.
Very handy tool when you are on the run.

A lot of sites made their reviews

A great video review from GiveMeApps here

One of the greatest Android reviewing sites AndroidTapp made awesome review of Ruler App here

Another review on Apps 400 – Application Review Portal

Simple review from AndroNavi can be found here

Finally, where to download?

Open Google Play on your phone or tablet and search for “Ruler App”, or if you view this page on your device click on this link:

If you like the app or have any feedback or recommendations, please post a review on the app store.