This tool calculates the complete transmission/drivetrain ratio (engine RPM : wheel RPM) of every gear in a particular transmission setup and the engine speed at any road speed, many gearboxes and transmission components can be selected, or you can manually enter gear ratios of your choice.

Gear ratios are collected from various sources including here, here and a Haynes service manual. They are correct as far as I know, your ratios may also vary due to the huge number of aftermarket transmission modifications available for the Land Rover, ensure the ratios match your transmission before doing anything! It also allows impossible transmission sets, such as an Ashcroft transfer box with an overdrive.