Screenshots

Here is the main window of YesCalculator. Three numeric fields are on the left.
Text can be entered into any one of these three fields. Entered value is automatically converted to selected measurement units of other two fields.

Clicking on the measurement category invokes the category selection window

Clicking on the measurement unit invokes the unit selection within current category

Sometimes it is useful to round the calculation result to certain number of decimal places (when calculating money for example). Rounding option can be changed from the main menu in the options window shown below.

See how it works yourself. Go to downloads section for your free 30 day trial.