The flight distance from London Heathrow Airport to Dublin Airport is 280 miles / 451 km
280 air miles between Dublin and Heathrow, London.
From Dublin, Ireland to London, England is 459 kilometres or 285 miles.
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It is cheaper to fly from London to Dublin than to rent a car in London and drive (and catch a ferry across the Irish sea) to Dublin. If you shop around you can get some very good value air fairs from London to Dublin.
About 4,129 air miles.
About 160 miles. Some or all of that would be by ferry or air.
About 159 air miles to Halifax, England OR 2,255 air miles to Halifax, Canada.
By car: 3 142 kmBy plane: min. 7 h (with the London connexion)
There is no direct ferry from London to Dublin. You can get ferries to Dublin from Holyhead or Liverpool. You would need to travel to them from London to get a ferry. The total distance, including the ferry, would be about 586 kilometres or 364 miles, though that would depend on your route.
London is better
Cardiff is in Wales. Dublin is in Ireland. Edinburgh is in Scotland. London is in England.
This will be a decision of air traffic controllers. Many flights coming from London and other parts of Europe that are heading to North America, fly over the south of England and Wales, over the south of Ireland and on across the Atlantic. That can mean that it can be a busy route, so the alternative for London to Dublin flights is to fly north towards Manchester and then across to Dublin.