ModelScaleCalc

This app can be used to easily convert from any unit in any scale to any other unit in any other scale. I use the tool often for scratch building projects.

Simply enter the amount, unit (defaults to cm) and scale(defaults to 1/1) to convert from and select the units and scale to convert to. Click the button and the result will be displayed instantly.

You can also use the second calculator to find the scale of an item.