Depending on how exactly it is done anywhere from 5 to 10 times as much.

Or in other words: Synthetic fuels are bullshit. They are incredibly wasteful in terms of energy and thus they are super expensive. They are a greenwashing solution to the problem that cars have become.

The actual solution to climate friendly mobility are less cars. We can't just electrify all cars on the planet. We need viable alternatives to cars like public transport, bicycle infrastructure and cities build for walkability.