From BlenderWiki
Numeric transformations
Mode: Object and Edit modes
Hotkey: G/R/S, then + NumPad/- NumPad and 0 NumPad-9 NumPad or Keyboard 0-9
Description
When doing a transformation, instead of using the mouse (imprecise work), you can directly pass a precise numeric value.
Hit - NumPad (on a French keyboard, the minus is under the number 6 key, so you must use the Numpad) if you want negative values, and then a numeric value. You can see the values in the header of the 3D View. If you were using an axis constraint (global or local), the value is applied to that axis. If there is no axis constraint and you want to choose which axis to control, you can use ⇆ Tab to switch from any of the axis (a cursor appears after the “active” value). You can cancel a typed value by hitting ← Backspace once, and you can return to a mouse control by hitting ← Backspace twice.
As with normal mouse control, you validate a transform with LMB 
or ↵ Enter, and cancel it with RMB 
or Esc.
Hints
You can use the keyboard’s . and the numeric keypad’s . NumPad for decimals entry. Be aware that older versions of Blender may not allow the use of the numeric keypad’s . NumPad for entering decimals.
