Convex: The Smart Converter for iOS

There are countless reasons that one might need to convert from one unit to another. Maybe you are an mechanical engineer who needs to convert your water pressure from inches of mercury to kilopascals. Or maybe you are just a high school student who wants to convert square feet to square meters for a geometry problem. Convex is an app that converts a variety of measurements between different units and does so with a simple, intuitive and beautiful package.

There are lots of apps out there that convert between units of measurement on the app store and claim to be the best, the easiest or the most powerful. An example of a great measurement conversion app is Convertbot, by Tapbots. Clearly, these two apps are similar, from the wheel of units that the app is based around to the clever ways that each of the different measurements are displayed. But how does Convex stack up?

Why Convex?

Convex aims to be “a revolutionary, stylish converter for iPhone and iPad that is so smart, it actually understands you.” And it really does make the job of converting to and from different units a lot of fun. The main source of all the joy is its use of a wheel which can be rotated, animated widgets for each measurement which can be manipulated by swiping, the arrows on either side, or by typing the measurement value manually.

Convex consists of a main menu and multiple widgets like this hard drive.

Convex consists of a main menu and multiple widgets like this hard drive.

As for the variety of Convex’s functionality, the wheel offers 20 categories of measurement that range from radioactivity to data size. For each of these categories, you can access 40-50 different units by tapping the unit name under the value at the top. That adds up to a lot of possible conversions and infinite ways to use this app. To set up a conversion, you first select two units which you would like to use. Then you adjust the value of the measurement and the app converts your measurement to the unit on the right automatically. If you want to convert back to the original unit, just tap the button between the two units. It’s that simple!

The Interface

The interface for Convex is very fun but also functional. Basically, the application’s wheel, which appears when you open the app, spins around to different categories of measurement and when you click on one of the measurements, a unique interactive graphic widget with which you control the measurement. For example, when you click on the water droplet, an animated stream of water appears. You can adjust the volume of liquid up or down by swiping up or down on the water flow. To add to this, each widget makes sounds appropriate to their measurement, specifically the sound of water flowing for the water widget.

Swipe up or down to regulate the volume of liquid you want to convert.

Likewise, the hourglass widget used for measuring time makes the sound of sand moving and the gear metaphor used for power makes the sound of clinking gears. And if you don’t like the widgets and metaphors or they are not precise enough for your needs, you can always swipe down from the top and reveal a white text bar in which you can type the exact value that you want for your measurement. Overall, the design is one of the most intuitive and creative that I have seen in a utility app.

Sharing Options

Conveniently, the app lets you share your conversions right from either the main menu screen or any of the individual widget screens. It also gives you the option to share through email and Twitter. Additionally, you can copy it to the clipboard or even save it as a voice recording. So if you are working with a partner on a project, this app makes it extremely simple to share the results of your conversions in a number of ways.

Convex uses a clever gear metaphor for power and has a great sharing system.


Convex is generally very smooth on my 2-year-old iPhone 4, but it is not perfect. The wheel at the beginning is pretty smooth, but some of the graphics on the different measurements get pretty choppy. This is especially evident and annoying when you are trying to move the arrows which reside on both sides of the widget, and you can’t get the measurement right because it keeps jumping up and down because of lag.This is not a huge problem because you can manually type in measurements, but it is something to keep in mind. However, this is not to say that the app is not usable by any means — actually, quite the opposite. For the most part, most aspects of the app run very smoothly.

Widgets for pressure and area conversion adjustment.


Convex is a great option for anyone who needs to do some quick conversions. Able to do almost any conversion imaginable, Convex goes about it in a fun and intuitive way that is easy to understand and master. Its beautiful interface and creative widgets just add to the charm and appeal this app possesses. Despite a couple of performance hiccups (which hopefully will be resolved in future updates), the app is smooth and functional.

Though I’ve only used Convex’s biggest competition, Convertbot, a couple of times, I can’t imagine that it trumps this app by much if any. I thoroughly enjoy using this app and would recommend it to anyone.


The Smart Converter for iOS: A simple and fun unit conversion app for iPhone