Its not always accurate.

While the user interface is okay, I dont like the wheel selection for units
I can live with it, though.
Unfortunately, there is another problem: its not always accurate.
Accuracy is important to me in a conversion app.
When I test conversion apps, I run 5 conversions. Here are my results from this app:
Length: passed (1 mile = 63,360 inches).
Area: passed (1 acre = 43,560 sq. ft.).
Volume: failed (1 US gallon ≠ 767.832 teaspoons; should be exactly 768).
Weight: passed (1 stone = 224 oz).
Temperature: passed (32℉ = 0℃, -40℉ = -40℃).
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This passed 4 out of 5 categories.
Overall, Im giving this app 4 stars for passing 4 out of 5 tests, and for a user interface that is pretty well done.
*Note: a previous reviewer questioned the conversion accuracy of acre to square feet. I believe that individual was looking at "Are", not acre. An are is 100 square meters, or about 1076 square feet.

MoonSmiles about iConvert - Unit and Currency