How many kilograms of grapes does it take to make one bottle of wine?

Approximately 1-1.2kg of grapes.

However, this depends on how hard the grapes are pressed. If you are only using the free-run juice which drains off the fruit without pressing, you will obtain less juice. The harder the grapes are pressed, the more juice is obtained. However, a larger quantity of juice obtained generally equates to lower quality with tannins and bitter flavours extracted.