Tech gadgets: Weights or measures, converted on the fly

Do you automatically know how many kilograms are in a pound? It's 0.45359237.

You probably convert units of currency, measurement and more from one type to another often. Doing these calculations mentally can be tricky, so let an app do it.

Convertible: The Ultimate Unit Converter on iOS stands out from many other apps of its type. It can convert between many units, and it's visually pleasing. The interface is designed to be intuitive, with clear use of categories to organize units into length, weight, speed and so on.

Colored sections make it clear what each part of the app is for. Swapping between, for example, United States customary units and metric units is as simple as tapping on the words and selecting a different measurement standard from the list that slides into view.

The app costs $2 and there's little to dislike about it.

Konvert, $1 on iOS, feels similar to Convertible, and its interface is extremely clear. But the app works differently, because it's designed like a touch-screen calculator. It also requires more gestures to navigate its options and settings.

On Android, Flib is a similar design-centric app. It's easy to use, and its visuals stand out. It has a few neat extras like putting the conversions you use most frequently at the top of its tilelike main menu.

For converting arcane or unusual units from one type to another, one great option is Convert Everything on Android. It can convert units as common as length and as odd as windchill or magnetic flux.

The interface is a little strange, though: Each unit is listed in alphabetical order. This can be confusing, but there's a prominent search box so you can quickly find "feet" or "kilograms," for example, and you can add a conversion to a favorites list.

Sometimes the app's Spartan interface can be a little confusing. But it is powerful, and it's free.