How much room do you need to launch a hot air balloon?

Generally an area as long as the height of the balloon standing up, with at least 3-4 metres or longer (depending on the size of the balloon) for the crown line that helps stabilise the balloon as it is being inflated. The width should be about half the height, but this can vary as there is some leeway, particularly if there are balloons being inflated together side by side.